UELVE MBC/v0.1
Contents
Basics
- A lightweight (200 kg) 3 occupant vehicle design that can be mostly DIY constructed.
- Although intended as an EU Category L7e "Heavy Quadricycle" it can also be the basis for a USA "NEV" or a pedal-car, or E-bike "pedal assist" motors installed.
- Dimensions 1.5 x 3.1 x 1.1 metres for a front surface area of approx 1.5 sq. metres
- Geodesic Frame skeleton is bamboo and PVC pipes connected together with 3D-printed software-generated "Nodes", which are then entirely encased (all Nodes and pipes) in Epoxy Resin and Kevlar, Hemp, Flax or other high-strength cloth layers.
- Double wishbone suspension is expected to be fitted at the front, whilst the rear may be swing-arm, Double-wishbone or Macpherson. This revision uses swing-arms at the rear.
- Body panels are twin layers of Fire-resistant Non-woven Polyester with a hot-glued 4 layer latticework "Hobbycraft" 9x1mm bamboo frame inside (9x1mm is easily bendable) to create compound curves. Label-gun "barbs" every 50 mm on a grid spacing will pin the two polyester sheets at a regular 10mm spacing, and Soudal Fire-resistant Expanding foam injected into the gap. After 2 days foam curing the panels are surprisingly strong and very light. 90 degree "wood furniture repair" brackets are embedded with Araldite 2-part Epoxy directly inside the panel at regular intervals.
Road-legal Compliance
It is without any doubt whatsoever entirely your responsibility and yours alone to check your local Laws as to whether the vehicle thay you are about to spend several thousand dollars on may even be driven on roads with other traffic. Even once built it is still solely and exclusively your responsibility to ensure that your hand-built vehicle is safe and legal. It is also unquestionably your sole and exclusive responsibility to ensure that your vehicle which you decided on your own cognizance to construct and then drive is properly Taxed, Insured, and well-maintained.
In the United Kingdom for example a self-built personal-use one-off vehicle under 350 kg may undergo a "Motorcycle Single-Vehicle Approval" test and if deemed safe and road-worthy receive a Q-Plate Registration. It then still also needs Tax, Insurance, and an MOT every year, just like any other Road-legal vehicle.
Other countries however simply flat-out prohibit individuals from driving their own self-built cars on roads with other road-users. There is no road-worthiness test that can be taken: it's just plain illegal to even drive your own hand-built vehicle in that country. You may be able however to use this frame to create a "pedal car" or "pedal assist 4-wheeled electric bicycle", at which point you will need to check your Local Laws regarding e-bikes. There will almost certainly for example be a power limit and a maximum "assist" speed limit.
Do not proceed with a build until you have checked your Local Laws.
If you proceed there is absolutely no Warranty or fitness for purpose expressed or implied by or through these Build Instructions. You and you alone are exclusively responsible for your actions and decisions.
Structural Integrity simulation
Checking the geodesic frame integrity was done with a faithful scale model made from straws and hot-glue. Any point that a hard twisting force caused warping easily identified Nodes requiring additional pipes. An actual software simulation has not been carried out because of the complexity, although using ODE either in python or c++ would be relatively straightforward: the entire Vertices and Nodes are all available.
The only thing is that every body panel, by virtue of being part of the structural integrity, would also have to be added and simulated, most likely in basic form of simple triangles connected to Nodes as well as pipes (at regular intervals) as well as to each other.
The advantage of ODE is that it integrates well with libSDL, for real-time 3D display, which would allow the Simulated vehicle to be driven across "terrains" for testing out structural strength. Peeping into the forces on Nodes would allow determining if the vehicle will withstand road usage.
Without such simulation this first prototype is going to just be massively over-engineered. Aixam Ligier Micro-cars from the late 80s and early 90s were thin plastic shells onto which 18x18x1.5mm box steel sub-frames holding the front and rear suspension. Using at least a 2 mm box steel "Ladder" Frame running down the entire vehicle, similar to the Citroen 2CV which was two and a half times heavier than this Category L7e vehicle should give a fair degree of confidence: we will soon find out.
Frame Concept
Blue pipes are 1m measure sticks. Note that the body takes whatever form we would like.
Skeleton frame using 3D-printed software-generated "Nodes" onto which a mixture of 21.5 mm PVC and 8-12 mm bamboo are loosely glued. A second phase involves Kevlar-Resin "wrapping" of the full skeleton, burying both Nodes and Pipes which were only there as a guide ("former")
CAD Source Code
If you use windows, tough. If you use a mac, you're just about in luck but have a lot of work ahead of you. If you use a GNU/Linux distro, you are on the right track and your life will be a lot easier. Assuming Debian, assuming you know what you are doing:
- apt-get install python2.7 git openscad ps2pdf enscript wget debootstrap schroot
- wget --mirror --no-parent -c http://lkcl.net/vehicle_3d
- git clone http://lkcl.net/vehicle_3d/.git
yes, really, python 2.7. you may need a debian/10 chroot for it (hence debootstrap and schroot). no, python 2.7 is not out-of-date despite what the Python Software Foundation insist on telling you.
you will need a high-end system for running OpenSCAD with this complex design. 16 GB RAM is a bare minimum. Intel Core i7 4.8 ghz is barely adequate. Integrated Graphics likewise is adequate. Low-end systems ("budget" machines) not designed for 3D CAD work will be completely intolerable.
Build
- Log and pictures - [1]
Prototype 1 Build Procedure
build log on endless sphere https://endless-sphere.com/forums/viewtopic.php?f=34&t=118802&p=1747637#p1747637
build diagrams with Node and pipe numbering can be found here http://lkcl.net/vehicle_3d/pdf/
- Use PVC and bamboo skeleton frame members joined to 3D-printed software-generated Nodes
- Wrap corners in epoxy-impregnated tape
- Wrap the length of tube bodies and the Nodes they are seated on in overlapping epoxy-impregnated tape as needed for additional structural integrity
- For attachment points to metal components, embed metal mounting interface plates/mounts/components in epoxy-impregnated tape just like the corners to attach firmly to the underlying skeleton
- Construct bodywork panel "lattice" frames, cover them in polyester (Dacron), hot-glued to the lattice, punch label-gun barbs through both layers at regular intervals and fill with Fire-resistant Expanding Foam (e.g. Soudal)
Skeleton Frame Phase
BOM
estimated
- 300 metres bamboo canes between 8 to 13 mm diameter, or 300 metres PVC or other pipe or straight sticks up to 13mm. (structural strength is non-critical)
- 200 metres OD 21.5 mm ("Floplast") PVC waste pipe, ID 19.5 mm (again: these are not structural)
- 500 metres 25mm width "Painter's" Masking tape
- 15 20g tubes of rubbery glue (Loctite Extreme, red tube - not Loctite Extreme Epoxy!). do not use hot-glue unless upgrading the 3D-printed nodes to PolyCarb or PETG: PLA deforms at only 60C. do not use strong epoxy or superglue
- 3 tubes Araldite Epoxy
- 5 kg PLA for 3D printing of "Nodes"
- Box of 200 hot-glue sticks
Tools
- 3D printer with 0.8mm nozzle, set layer height of 0.6 mm and 0.2mm "support towers", full coverage. Nodes are complex.
- Usual pliers and files for removing 3D support
- Full wrap eye protection (from high velocity 3D print support material during removal phase: it can get behind your eyes and start scratching)
- Hacksaw and Mitre (90 degree angle cutting)
- Sharp pencil (hard)
- 0.3mm black pen (non-biro) indelible ink for writing on Masking tape
- 1 metre metal ruler and tape measure
- A4 printer
- 25 metres string (for tensioning). garden twine is sufficient.
- Hot-glue gun
- Sharp robust scissors (kitchen scissors sufficient)
Assembly advice
- Measure twice cut once!
- Cutting accuracy on pipes to around +/- 0.15 to 0.2 mm is pretty crucial. The geodesic frame shape amplifies errors which causes cascading problems that require partial disassembly to correct (hence the rubbery glue and masking tape instead of strong rigid epoxy or cyanoacrylate).
- Use the 3D CAD to create 2D screen-shots then draw Node and Pipe numbers on them. As each Node is 3D printed place the same Node number on it, written on masking tape. Print out pipe connectivity listings and cut them into strips that are taped onto the pipe during the cutting phase. Be very strict and patient here because there are 135 Nodes and around 400 pipes to assemble. When (not if) mistakes are made you want to be able to cross-reference the poles and nodes in-situ against the build diagram, and you can't do that unless the in-situ parts are properly identifiable.
- Use the 3D CAD to zoom in onto Nodes in order to get their orientation correct. Sometimes the 2D A4-printed screenshots can be sufficient, but some Nodes are very similar. Make absolutely certain that the angle in all three axes is orientated to within under 2-3 degrees: greater than that results in pipes moving out of position and not seating correctly, and an error-cascade begins. If necessary cut all tape free from all pipes on a node, scrape off the rubbery glue then reglue and retape. Do not attempt to remove a Node from in the middle of an assembly.
- Pipes must be cut dead flat at 90 degrees. Use a file to ensure uneven ends are level: cutting is best done using a Mitre, circular bench saw, or even better a hand-hacksaw held in a cutting jig. It is best to slightly overcut (0.25 to 0.5 mm) then file down, although this can add significantly to build time. Do not attempt to use "undercut" 13 mm OD pipes, or if risking doing so add layers of thin cardboard glued in the seat of the Node (only up to around 2 mm), in order to get its length back up. This trick will not work with the PVC pipes: there is a 19 mm "inset" on the Node which fits inside the 21.5 mm pipe. Undercut pipes are best put aside and used elsewhere in a shorter location.
- Bamboo can be tricky: often it is not dead-straight. Remember that the ends have to be perpendicular ends TO EACH OTHER, not to whatever bend happens to be in the bamboo! If unsure, put the uncut pole aside and select another. If you fail to get the pipe cuts perfectly perpendicular it will result in error-cascades.
- Start from a flat fully-triangulated base of parts then when going vertical locate 3 pipes onto one node and create tetrahedra on the flat base. Use the Node seats as an accurate guide as to direction the pipe needs to go. Once one tetrahedra is created find another right next to it and asssemble that. Do not attempt to assemble from the outside inwards (and try to meet in the middle), work from one side to the other or from the middle to the outside: climbing *inside* the frame to glue-and-tape is very tricky.
- If when it comes to putting in single pipes towards the near-completion of an assembly there is a gap that cannot be bridged by using the masking tape to "pull" the pipe at both ends, use string wrapped carefully between other pipes on the same node at both ends, tie tightly then use another piece of bamboo to prise the twine apart, or use more twine, tying that to other nodes in the same plane to get heavy tension and push the gap shut. Be extra careful as this is where mistakes cascade and get noticed.
- Towards the end as the final poles go in, the redundancy of the bracing will begin to show up any cutting and angle errors, significantly. Do NOT be tempted to change pole lengths from those given in the BOM (except if they were inaccurately cut in the first place).
- Aside from angle orientation errors trust the direction that the pad cones point in. Follow them line-of-sight to their destination Node. If you have the assembly correct up to that point, each new *correctly perpendicular* pole of the correctly-cut length should definitely fit precisely. If the pole is not pointing at its Node seat at the other end, or is not perpendicular, you've made a mistake somewhere.
- Sometimes under the Masking tape the glue will come loose. It is possible to use even more masking tape to "pull" the pole against the Node seat, but eventually it gets unwieldy: that is the point to consider putting twine around instead.
- Always ensure that all poles are attached to their Node seats at all times. Test the assembly regularly by lifting one corner off the ground, carefully, and even more carefully by clamping two Nodes down and deliberately twisting the frame. If assembled rigidly you should see Nodes actually rotating and bamboo poles bending quite significantly. Loose poles (8n need of reattaching) will easily show up with this test as the assembly will be very easy to push about. When all poles are fully attached to all pads, the "twist" test will definitely be hard, and will definitely visibly cause several poles to bow. Do not overdo the twisting.
- The entire frame is extremely light (under 10 kg) at this stage: turn each section upright or upside-down to make access easier, as needed.
Construction order
- Bonnet
- front (turn bonnet over, add front upside-down)
- dashboard (turn front nose-down, add dashboard)
- floor and floor support (keep front nose-down, add floor vertically)
- Driver seat box (on f!oot, after floor detachment from front)
- "Back" box (behind occupants)
- Door sides
- Roof (separate assembly resting on driver box and backbox)
- Rear frame
- Bumper
- Doors
Construct in 4 subassemblies:
- Bonnet, front, dashboard and 1/4 of the floor (assemble whole floor, along with floor support; brace - double-up the bamboo with epoxy - then separate at the footwell line)
- Driver seat-box, "Back" box on floor, door sides, then brace around the Driver seat-box and separate another 1/4 of the floor
- Roof and top section of the "Back box"
- Rear frame continuation of the remaining "Back box" and add bumper
The subassemblies may be tightly taped to each other for checking rigidity and overall assembly correctness. After the Cloth-Resin Phase, bolt-holes will be drilled through, metal spacers inserted and epoxied in, so that the four sub-assemblies can be bolted together with Castle or Nylon lock-nuts.
Rear Section Assembly
The rear is very hard to identify "tetrahedra" and there are curved-arch roofline sections extending behind the two passengers. Follow this procedure for left side then mirror to right:
- CAREFULLY using hot-glue covering just the inner 13mm circle place a bamboo stick dead-upright in the cone. Bear in mind that the Joints are a cone, sphere, cylinder joined together and it is the CONE that points in the direction the stick has to go. You can if you like pre-prepare an 80 mm strip of Masking Tape around the cone which is squashed around the hotglue. Do however keep the cone upright whilst the glue cools and hardens. OVERUSE OF HOTGLUE may melt the PLA so be extra careful: use less then add a second batch if necessary.
- When connecting Joints via Rods make absolutely certain the Nodes are not rotated incorrectly. Use the 3D CAD to get a proper visual feel for orientation if needed, but be accurate to within a few degrees. The hotglue will bend by about 5 degrees but fights it: two or more rods once incorrectly assembled at off-angles require disassembly and starting again. This is harder with hotglue than it is with Loctite Extreme rubbery-glue, so be extra careful and meticulous.
- Add Joint R3 to R4 (see Rear Section build diagram), then R13, then R14, followed by R11 onto R12-R3, and R14 onto R13-R11-R4 in that order
- Assemble NOT USING HOTGLUE but masking-tape and Loctite Extreme Glue (non-resin, rubbery) Rear Bumper B3-B2-B10-B11 at the bare minimum but if preferred include B6-B7 for a full rigid sub-assembly. 21.5 mm Floplast PVC Pipes tend to stick well and stay pointing in the right direction (as long as the PLA has been cleaned up and the PVC cut perfectly perpendicular).
- Do NOT attach B14 or B15 to the B6-7-2-3-10-11 sub-assembly.
- BackBox0/1 only have a single strut to R11 and R14 respectively. DO NOT join any other poles onto R11-13 to BackBox because these are actually part of the (detachable, bolted) Roof Assembly.
- Turn the BackBox Assembly face-down, it is much easier to add the pyramid and tetrahedra coming up next as they sit on their pads under gravity without falling off, prior to affixing (loose masking tape helps keep them roughly positioned)
- In a pyramid with R2 at the top hotglue the four pipes leading to BackBox-14/13/3/4. All four poles can actually be free-floating as long as care is taken.
- Attach the pyramid to the BackBox, noting that as a pyramid not a tetrahedron it will pull and push. Find an edge that pushes, hotglue the OTHER poles, wait for them to dry then prise in the final pole. Do not attempt to use hotglue to "pull" (unless twine is wrapped round, which is quite awkward)
- Attach poles leading to BackBox-14/13 onto R5, free-floating. Add the 21.5mm short section to R5, then attach the tetrahedra to R2 and BB13 and BB14.
- Attach the 21.5mm pipe to R6 but not R5 yet. Hot-glue the two very long poles onto R6 leading to BackBox-9/10, with care, leaving them free-floating but always allow the hotglue to set upright (i.e orientate the entire subassembly so that the pad - and pole - point upwards). Invert the tetrahedra and assemble on R5, BB9 and BB10.
- With the central line now rigid against the BackBox, the roof arch subassembly can be added. Hotglue R11 to BB14 and BB0, and R14 to BB15 and BB1. Add R4 towards BB15 and R3 towards B10. leave all pipes freestanding, bear in mind that the longer rods go to the same Node as the two down-pointing short ones.
- Drop the roof arch in place and hotglue all pads. The assembly will still rock sideways: it is an open arch.
- Connect R3 to R2 and R5: this will stiffen up the roof arch, but beware any cutting inaccuracies and Node angle inaccuracies, they will show up at this point (twine helps put poles under compression, whilst hotglue sets).
- Rear light / bumper sub-assembly can be added: B3 to R3-R4, B2 to R4-R2, B10 to BackBox14 should be sufficient to get started, first hotgluing bamboo rods carefully free-floating, leaving them unattached initially, position the sub-assembly under gravity.
- Add 21.5 mm B14 to B6-B10 using Loctite Extreme and masking tape, and let it set before moving on, checking that the UNATTACHED sub-assembly pipes (to R3, R4, R2 and BB14) are the correct length from their pads. Expect there to be some differences: first hotglue those poles that are a fraction AWAY from their pad (shift the other poles which are "too long" off-pad carefully) then once the hotglue sets fully bring in each "too long" pole one at a time. Make absolutely certain that the pole is definitely perpendicular to its pad, and if there is ever a gap greater than 5-6 mm STOP and re-check pole numbering and length. As each pole is hotglued expect the whole sub-frame to begin shifting about.
The remaining poles can be connected up with care: bamboo can if necessary be bent somewhat to get it into position (or a section broken off of the pad's wall), and if 6-10 mm bamboo poles are used rather than the full 13 mm it is possible to get glue onto the full pad surface (including under the pole's end) by shifting the pole around within its seat. If using hot-glue do this quickly and be prepared to use short squirts then follow up with a second layer.
Towards the end of the assembly process putting some rods under tension caused other rods to pull free from their pad. More twine was needed to put those back under compression, and eventually everything settled, although a lot of force was needed in some cases (doubled-up twine). This occurred on the other assemblies so it was not a surprise. In this case however at the roofline it turned out to be due to twisted (off-angle) Nodes. Emphasising that exact orientation really is important https://youtu.be/2mLlDseCrGU
Kevlar/Cloth-Resin phase
Adequate ventilation is critical at this phase. Epoxy resins can give off fumes. Make absolutely certain to read and follow all safety guidelines. Addittionally Kevlar is a non-destructable material. Cutting or sanding it releases micro-fibres which if breathed in can seriously damage your lungs, and other things. Again: look up and follow all safety guidelines. This is entirely your responsibility.
There are two main tasks here:
- cover all Nodes (just like in Bamboo Bike Club and Calfee Design)
- cover all Pipes. The pipes are in NO WAY structural: they are a guide.
All pipes and all Nodes need to be entirely cased in Cloth-Resin multiple layer wraps, fully interleaved. This is unlike in Bamboo Bikes which utilise the strength of the bamboo itself: here we use the bamboo (and PVC) as a former for the Kevlar/cloth. Instructions on how to do Cloth-Epoxy wrapping can be found from many sources.
BOM
- Fire-resistant Epoxy (FR4) available from MBFG.co.uk
- QTY 7of 1.29 kit Sicomin SR5550/SD5505 (fast hardener) available from MBFG
- QTY 18 metres 1.1m width 1414 (4mm weave/weft) Kevlar cloth
- Flax, hemp, or hessian (thick coarse linen)
- QTY 20 metres Kevlar "strip" 50mm wide (MBFG)
- Scrap paper
- QTY 10of 25 metre Masking tape 25mm wide
- long strips of cardboard (as appropriate) to be taped onto bamboo poles
Tools
- stippling brushes (QTY 100)
- Protective clothing, face masks, rubber gloves (thick heavy duty and blue nitrile)
- Mixing and measuring containers
- Mixing sticks
- Floor protective covering
- Sharp scissors
Recommendations
- Open the windows! make absolutely certain to get good ventilation.
- The assembly will start to get heavy, and may cause the collapse of un-epoxied Nodes that are face-down on the floor, particularly those with bamboo poles instead of Floplast. Consider a support jig or ensure that all Nodes are properly glued-up. The ones in contact with the floor were only using Loctite Extreme (rubbery), not hot-glue, and clearly not enough of either.
- Pack out any large gaps especially around 21.5 mm Node Seats with crumpled paper covered by Masking tape. Create a full sealed wrap with Masking tape around the Node so that resin is not wasted dripping inside. If this is not done a large amount of Kevlar and resin could be wasted filling up gaps, increasing overall weight.
- The packing should be done with the following thoughts in mind: "when wrapping strips of cloth, firstly will the cloth bunch and crumple at all, and secondly will it create an air-bubble if stretched taut?". These two questions if answered with a scrap piece of cloth as a tester will ensure cloth-resin-cloth contact on all layers.
- Prepare all tools and materials before beginning a resin batch. Once mixed you are on the clock before it hardens, you can't cut anything wearing gloves covered in resin, nor risk picking anything non-disposable up. https://youtu.be/3IsFua_lVg0
- Wear thick rubber heavy duty gloves then put disposable blue nitrile ones on the outside. Blue gloves break routinely, but they protect the heavy duty gloves from being completely covered in resin.
- For 21.5mm PVC pipes, where Nodes are mostly also 21.5 mm PVC, pre-prepare kevlar cloth strips 80-90 mm wide with "tails" at each end anywhere between 80 mm and 120 mm which will be used to wrap around the Node and Pipes at the other end. Split just before reaching the Node, so that the "tails" do not end up with airgaps on branching out.
- For bamboo poles similarly but under 50 mm wide strips (which will still wrap at least twice in some cases).
- For complex Nodes (over 6 pipes, especially bamboo close together, like a porcupine) cut the tails very short, then use small 1414 strips 1 in by 3 to 5 in long, to weave and dodge between the poles but still overlay the short "tails".
- Alternate between wrapping pipes and wrapping Nodes (with 50 mm MBFG Kevlar strips). Although the "tails" from the cloth wrapped around the pipe should join to other pipes and create good structural bonding in some cases it will be evident that the cross-over is inadequate. Use several layered strips anywhere from 6 to 18in by 25 to 50 mm to create adequate bonding between pipes, depending on situation.
- The Kevlar 50 mm strip from MBFG is expensive (and really high quality), so use very sparingly. Try to use long tails as much as possible, and only if those really will not adhere (concave indentation) use an appx 6 in or suitable length of 50 mm strip, laid at right-angles, to get the tails to behave. Do not wait for the resin to dry before doing this! Therefore, have a few 6in x 50 mm strips pre-cut.
- Also pre-cut some 1 x 4 in or so strips: on convex surfaces these can be extremely useful especially just where a 21.5 mm PVC Pipe meets a Node. Wait a little until the resin has become "gel-like" and you can stick two cloth surfaces together with these short "bridges" and pull them together.
- There are extremely cheap packs of 50 1in brushes on Amazon (under USD 10) which can be trimmed to 15 mm and used for "stippling". Stippling is best done when the resin has reached a gel-like consistency: at this point the fibres of the cloth beginning sticking to the brush, become coated with resin, and "string out" (like unprocessed cotton wool). This results in a chemical reaction between cloth and resin that increases strength and adhesion between layers.
- Discard the brush on each batch: at $0.15 per brush it is not worth recovering (of course if living in an isolated self-contained or Permaculture environment disregard this advice entirely). The measuring containers however can be reused at least twice but must be entirely emptied of the previous batch of resin, in order to ensure that the new batch measurements are completely accurate.
- In some locations the thin bamboo poles may be bending a lot, especially long ones. Rather than waste kevlar and resin bulking up, a trick is to put cardboard strips parallel to the bamboo then cover those. This can be useful to create good Panel attachment points apart from anything.
- Use the Silicomin SR5550 for lamination only: the FR4 is a potting (casting) resin and is way too viscous, you will end up using 30% more, as it fails to penetrate/soak the Kevlar. Use it instead as a final covering surface layer to give a degree of Fire-resistance
- After one (first) layer of Kevlar on 21.5 mm PVC consider using Industrial Hemp "hessian" style cloth. Cut to wrap twice (160 mm) do not add "tails", wrap it clean round the Kevlar. It will fall off, the first second and probably fourth time. Be patient: micro-fibres will form that eventually stick to the surface of the Kevlar. When they do, pull gently against the "stick", wrap twice then grip the pole and pull round (use both hands, do a motorcycle "throttle" revving thing), squeezing gently at the same time. Then depending on the situation add at least two 5in x 50 mm MBFG kevlar tape sections at both ends and consider in the middle as well. The ends cover partly the Kevlar-covered Node and partly the Hemp Hessian. Finally wrap the entire lot with a double helix of twine, after the resin begins to gel. https://youtu.be/fglGLtW4o8k
Frame Assembly Phase: metal mounts
TODO. front double-wishbone, generator, batteries, rear swingarms, Motor and CV Joints
Frame assembly
The idea here is to allow all four assemblies (front, middle, rear, roof) to be boltable to each other, which in turn implies placing a split tube at every Node that has been cut in half. A 75 mm M10 bolt with a Nylon locknut may then go through each. Each half tube (30 mm) must therefore be encased in Epoxy-cloth wrapped onto / into each Node, in exactly the same way as deployed by Calfee Design and the Bamboo Bike Club.
One technique would be to pre-wrap long lengths of 304 Tube then cut them, but cutting any indestructible cloth especially resin-soaked throws micro-fibres into the air which can damage lungs. Therefore to avoid this it is best to pre-cut the 304 tube and then wrap it. (If this is not preferred then it is your reponsibility to look up and follow Fibreglass cutting advice and to strictly follow the required Safety procedures)
However the logical chain does not stop there: the last thing we need is for the Tubes to be epoxied to the Nodes only to find that when all bolts are inserted and tightened the frame twists due to errors. To avoid this scenario all Tube-pairs should be pre-tightened with an M10 bolt and then epoxied to the Node, whilst the two Assemblies are Masking-taped / Twine-tied down firmly in place at every single point where a bolt is to be added. Under no circumstances should the M10 bolts be removed until every Tube-pair is epoxied and cured (approx 1 week for SR5550). Of course the only risk here is to accidentally end up wrapping over the gap between the Tube sections!
Assembly may take place "upright" with the middle section over the top of either the rear or the front, meaning that as long as the building in which assembly takes place has a ceiling over appx 2.4 metres it is achievable, having the advantage that a jig is not strictly necessary and the floorspace required is reduced to around 1.5 x 1.3 metres. Gravity for the most part keeps the sections together.
In some places L-brackets back-to-back can be used but it is critical not to treat these as structural.
Issues likely to be encountered
Be advised that if using superglue-baking-soda it will expand like construction foam! especially if the superglue has a high acid content. Be prepared to mask off the tube so that the expansion does not result in interference with the M10 bolts. https://youtu.be/Nj0OImHFjFM
The Stainless steel 316 tubes absolutely must be adequately glued in. If they come loose the vehicle could literally fall apart which is dangerous. Consider roughening the outer surface significantly, especially of polished 316, even to the extent of using a hacksaw to score regular (short, 4mm) deep "X" or "V" patterns (no more than 0.15 mm deep).
BOM
- 304 Stainless steel 12mm OD 1mm thick tube, 3 metres, cut to 30 mm sections
- 75 mm M10 Bolts, zinc plated or pure stainless steel
- M10 Nylon locknuts
- 50 mm MBFG Kevlar tape
- 1414 Aramid Cloth, cut to 1in sections between 4 to 8 in long.
- Masking tape and twine
- Silicomin SR5550 resin and fast hardener
- Fast-acting Araldite Epoxy resin, FR4 potting resin, or Superglue and Baking Soda https://www.youtube.com/watch?v=eP3xJIJ-TbU
- 30x30 mm L-brackets and M5 bolts, 12 mm, with lock-nuts (or Loctite threadlock)
Instructions
- Cut two wraps of 1414 Aramid instead (30 mm by 120 mm). Do not use the 50 mm MBFG Kevlar tape, it is too thick and dislikes sticking (de-laminates, repeatedly, due to the angle of curvature on the pipe).
- "Roughen" the surface of each tube with a hacksaw, cutting small shallow "V" or "X" patterns no more than 0.15 mm deep.
- Wrap each 30 mm 304 stainless steel section once with Kevlar, lengthwise, ensuring that there is no overlap on the ends (bare steel). Leave them all to cure for at least 2 days.
- Pair up the Epoxied tubes and assemble them with an M10 bolt and nut, but without the Nylon insert into the nut.
- Assemble the Rear, roof, and Floor Sections upright, check that they are seated correctly, and are all Epoxy-wrapped at the Assembly points, and all Pipes leading to other Nodes are also wrapped.
- Tie and/or Masking-tape the Assemblies together in such a way that access to the Nodes to which the Tube-pairs are to be Araldited is not impeded, and that the attachment is not so tight that it stresses (bends) any of the pipes.
- For each Tube-pair choose a location and angle for attachment such that access with a spanner and hex-wrench socket at both ends is achievable. Both ends need not be turnable but at least one end does. Also ensure if desirable that panels need not be removed for the M10 bolt and nut to be accessible. Also to aid inspection, during maintenance reviews, do not hide the Tubes.
- If necessary cut a channel through the Node and remove the paper and Masking Tape underneath, but if doing so only do this outside and under no circumstances inside a domestic environment.
- Prepare the Araldite Epoxy (or other glue) and apply sufficient on both halves of the Tube-pair to affix each half-tube to each Node-half. Use either Masking tape or a G-clamp (with soft cloth or Kitchen towel to protect the Tube-pair). Use enough to ensure that when further Wrapping is carried out there will be no air-pockets.
- Once sufficiently set remove the Masking tape / G-clamp and prepare some more Silicomin SR5550, and lay down several wraps around the Node and each half-tube. Take extreme care not to get resin or Kevlar over the join point between each Tube-half! If practical go all the way round. Build up layers to a depth of at least 8 mm around each Tube. The Tubes are going to bear a high load: they cannot be permitted to twist about.
- An alternative to the 1414 Aramid cloth is the MBFG Kevlar tape but it must be folded in half, lengthwise. This is tricky and meticulous but doable.
- If feeling particularly paranoid attach 'two Tube-pairs, one on each side of the Node, for both strength and redundancy, especially at the windshield, Floor, and Door-frame.
- Leave all Tube-pairs in-situ for at least 7 days (SR5550 curing time). Do not be tempted to undo any M10 bolts during this time.
Alternative technique
A second technique (with some risk) is to embed the actual M10 hex-bolt in Kevlar-resin wraps onto one Node-half and to have the short tube on the other. This avoids the bolt turning unless a pair of spanners is used, which may be more convenient.
The only major issues to watch out for are:
- alignment of all M10 Bolts and associated single 304 tube.
- not to overtighten. When two 304 tubes are used they cannot compress.
- overtightening risks stressing the frame as the bolt head is embedded in it.
- if the bolt is ever stripped or damaged it is a severe repair problem.
- the bolts must all point in the direction that the assemblies are to be affixed (by sliding all bolts into all tubes, simultaneously). remember that whatever assembly is being attached must slide cleanly in one and only one direction, thus all bolts must align in that direction. one bolt pointing even at two degrees off-kilter could mean that the bolt simply cannot be assembled or even disassembed.
- If resin drips onto the threads during wrapping the bolt has to be repaired in-situ, it cannot be removed.
Although the embedding of an M10 bolt into the roof at the top corner of the doorframe saves on resources and weight it is highly risky: great care should be taken. Covering exposed portions of the bolt with masking tape, the inside of the stainless tubes as well, and insertion of thin cardboard between sections during wrapping or gluing should be considered.
Panels Phase
The general idea here is to create a lattice-work (trellis-like) frame in whatever compound curve shapes are required, with two layers of Polyester cloth glued top and bottom, pinned with Label-gun "barbs" and filled with expanding foam. This creates a remarkably strong and light-weight panel using off-the-shelf DIY / Home materials.
90 degree metal brackets are embedded within the panel, allowing it to be bolted or screwed onto the frame.
An important note when assembling panels: given that the frame itself is to be used in effect as a "jig" waiting for the foam to set it is critical that panels are assembled symmetrically. If done one at a time any pressure may cause frame twisting.
BOM
- 6 sq.m "top" surface cloth. Fire-resistant polyester recommended.
- 6 sq.m "bottom" surface cloth. Fire-resistant black "Sofa covering replacement" recommended
- 90 degree metal brackets (40 mm x 20 mm, 1.5-8 mm thick) with screw holes
- Hotglue sticks
- QTY 500of 9 mm x 1 mm x 300 mm bamboo DIY craft sticks
- QTY 5,000of 10 or 12 mm plastic barbs
- 8 sq.m very cheap cardboard, appx 3-4 mm thick. Lighter (cheaper) the better. Thin card, large holes. Corrugated cardboard would do in a pinch.
- Soudal Fire-resistant expanding foam
- Araldite fast-setting two-part epoxy glue.
- TBC
Tools
- Sharp Wire cutters (best way to snip the DIY bamboo) or tin-snips
- Blue nitrile gloves (and heavy-duty ones if preferred, underneath)
- Construction foam gun
- Foam-gun cleaner can (pressurised acetone)
- Acetone (for cleaning hands)
- Strong but disposable floor protection covering material
- Disposable Replacement Foam gun "straws"
- Twine
- Label Gun with spare replacement needles
- Hotglue gun
- Sharp scissors
- Screwdriver
- 2.5 mm drill bit (and drill)
- TBC
Assembly
TODO
- Only do hotgluing and foam in well-ventilated conditions. Both give off fumes.
- Wear suitable clothing and lay down protective disposable mats/cloth/sheet: the mess the foam makes is horrendous. Hotglue also "strings" in quite beautiful but annoying "spider" strands, so dress appropriately.
- At suitable locations affix 90 degree brackets to the frame (drill, screw or attach a second bracket and use bolts). Near each Node and in the middle of long pipes is best. The flat edge of each bracket is to be encased *inside* the panel, therefore the brackets need to be attached pointing *outwards* from the frame.
- Ensure that the brackets and screws/nuts/bolts are accessible! It is no good putting the panel together if it cannot be removed! At some point repairs or replacement are needed.
- Ensure that at least three bamboo strips are affixed directly to each bracket, triangulating in three dimensions. Turn one section of bamboo on its side so as to prevent rotation of the bracket (and the frame edge to whch it is attached).
- Begin laying down and hot-gluing bamboo, starting from a Node, working along pipes, bending over other pipes, until reaching another final Node for the edge of the panel. Lattice holes vary but a very rough guide would be between 50 and 150 mm.
- Try not to hotglue the polyester cloth to the lattice until each subsection (within a Frame Triangle, usually) is completed. The goal here is not to have to remove the 90 degree brackets, and to create the entire panel "in-situ"
- For square panels lay down four interlocking layers: two latitudinally, two longitudinally. Leave holes (vertically) except when each 300 mm bamboo strip runs out: then use a short section to glue and extend. Alternatively a line of hotglue onto Masking tape pressed and wrapped roud the two ends can be quite effective.
- Cutting short strips and hotgluing them inside takes considerable time, and also stops foam from expanding easily across the panel lattice. Avoid this scenario. The foam will fill the gap.
- For hexagonal or triangular panels lay down a triangular pattern.
- Once confident with the panel trellis shape, epoxy the brackets onto the bamboo with as much epoxy as you dare. Preferably you should have arranged the bamboo trellis to "cross" right where each bracket is. Ensure that the bracket is really firmly epoxied, encasing it is best. Do not mess about. Alternatively superglue and baking soda may be used but bear in mind it may expand, so ensure masking tape is used to keep it in check and directed inside the latticework.
- Remove the trellis/lattice frame from its attachment points.
- Cover the brackets (and the frame) with black non-woven polyester cloth, on the underside, in the size of the panel, but slightly larger (around 4-5 cm). If necessary cut and patch together in sections.
- Cut out cardboard to fit each trellis hole, and punch holes at approx 40 mm intervals in regular grid patterns (for the label gun barbs). In the middle of the grid put a small dab of hotglue to affix the cardboard onto the black non-woven polyester.
- Hot-glue the top layer of cloth all around the panel, but only up to around 15 in depth. If it is a huge panel it may be necessary to only do a portion at a time (including when filling with foam, which will be great fun. Do not overfill!)
- Punch barbs through the top layer, through the cardboard holes, through the bottom layer of polyester. Repeat 4,000 times.
- Slowly inject Soudal Fire-resistant foam into the panel. Bear in mind it will create huge pressure possibly snapping the label barbs if too great, so take care, take time. Plus, it really does expand considerably.
- Clean up the Foam Gun quickly, by squirting Acetone down it.
- Clear up the horrendous mess the expanding foam makes, it is not nice stuff.
- Leave the panel alone for 48 hours. In fact, just leave the panel alone. Do not be tempted to poke the bubbles that form between the polyester cloth, although it is quite fun.
- On large panels continue the process of hotgluing sections of the top polyester, label-barbing, then foam-injection, until completed. Although tedious ensure that the Foam Gun is cleaned every single time. Failing to do so results very quickly in finding out why it is necessary to clean it immediately. REALLY do not do either the Foam Injection or cleaning inside a domestic environment (outdoors is fine). Both acetone cleaner and the Foam itself are nasty stuff, despite being DIY materials. Wear appropriate clothing and Organic Filtration Masks.
Videos
https://www.youtube.com/playlist?list=PLBtNqZjUZB81KyRPnMHSmX-vF8i7h5kcA