LifeCat 1.0/Research Development/Previous Design Analysis
Contents
Overview
Here is some analysis of the LifeTrac III from community members and on-site users
LifeTrac III User Review
This is a collection of onsite analysis of the design and user input. It also provides potential solutions for the LifeTrac IV and LifeCat
- Non-standard tool loading mechanism means that existing forks and other accessories for Bobcats and such won't work
- Redesign to incorporate the Bob-Tach attachment method. Also known as the universal skid loader attachment method.
- Can try to still keep simple OSE 3-point attachment for use with smaller tools
- Loading mechanism is too far out
- Need to redesign to bring it to just in front of the vehicle. Will need to redesign cylinders and lifting arm accordingly. A bent loader arm will suffice.
- Wheel assembly and motor is difficult to mount
- Change motor to direct coupling to hub. Just rear wheel drive and connected through the tracks. Even with this still need a mechanism for easy attachment for front wheels.
- Redesign current configuration into a modular unit that can be easily bolted on and off. This is being done with the quick connect wheels for the LifeTrac IV
- Feet can touch the ground because there is no bottom plate and is a very large safety hazard
- Mount a bottom skid plate
- No head protection from falling debris
- Need a roof plate
- Seat being so far back makes it difficult to see precisely where loader is for intricate work
- Move seat forward to mid level of tractor. But have issues with the bars there and everything. Would likely need to move cross members above frame
- Controls are difficult
- Integrate foot pedals for loader arm and QA plate and rotate hydraulic levers so that they move forward and backwards and are on each side of the user's arms
- Cross members are visual obstructions
- Move to above top frame members vs below them to improve visability and head clearance
- Tipping stability with lifting heavy objects
- Due to straight loader arms, tipping load is very low. Additional weight needs to be mounted as far rearward as possible to increase the tipping load and thus the carrying capacity
- No analysis done on any of frame members for structural stability under heavy load
- FEA needs to be done on the frame. This include an understanding of dynamic load analysis.
- Stock 3x6" comes in 20' and 40'
- Keep this in mind for any redesign
- No protection for hydraulic motors from ground objects
- Incorporate protective covering or skid plate between motors and ground
OSE Europe Lifetrac Design Safety Discussion
Here is the link to the full forum discussion.
Frame
- No engineering analysis done on any components of the frame for the loads encountered
- When the machines tracks rotate in opposite directions this turns the machine but the load is transferred to the frame. Because the wheels have a gap between them the force is not equally distributed along the bottom of the frame. The force travels through each wheel, to the corners of the base frame square, from there it is transmitted up the vertical frame and along the top square frame, all of the force meets in the center of the top frame along two parallel lines. Here you have placed a very large hole which the loader attaches to. From the top centre of the frame the force from the wheels is then transmitted to the centre of the base frame.
- Comment: Conventional machines which use tracks transfer the load from the track through a series of gears which span the entire length of the track and base frame. A conventional skid loader has the hydraulic lifter attached to a separate frame from the drivers cabin, this improves operator safety from moving parts, improves stability over the entire machine and increases load bearing capacity from the chassis I.e. it doesn't snap in half. The machine is most likely to snap in the middle of the bottom and top struts on which the wheels and loader are mounted. So two sets of forces are meeting at one point. This is the force from the wheels and the force from the loader.
- The construction using tubes bolted through the center is not good for dynamic loading as the bolts need to be sufficiently pre-stressed during assembly. This is not possible with thin-walled square tubing
- Comment: What are the proper forces/torques required in pre-stressing the bolts during assembly? From this we can calculate the required material thickness for square tubing to ensure no deformation during tightening.
- Considerable forces on the frame introduce bending moments on bolts which they are not designed to take
- Questionable engineering practice to place the longitudinal and cross-support members on different planes as it generates additional stress in the design as torsion and bending moments
- Potential Frame Solutions
- Welding the frame members together
- Welding a plate to both frame members to they can be bolted together with several bolts
- Using U-profiles instead of square tubes, You could
- weld them
- weld a head-plate to the crosswise frame members and bolt it to the longitudinal frame parts
- Place frame members all in the same plane
Wheel Motor Coupling
- Alignment between the motor, coupler, shaft and wheel needs to be precise to prevent failure with time due to the high forces involved.
Safety
- No roll-over protection
- No floor, side walls, roof, or restraining devices (Note: These should be getting addressed in LifeTrac IV)
- No independent brake in case of hydraulic pressure loss.
General Comments
- Trying to have the LifeTrac be both a skid steer and tractor ends up with a design that doesn't do either well
- Skid steers are very hard on the ground and thus not good for actual farming applications or over grass. However they are great for many other tasks and have a large versatility of tools and attachments otherwise
- Articulated/conventional steering with a longer frame design is much more suited for hauling and dragging machinery
Bolting Through HSS Tubing
One of the main design features of the LifeTrac II, III and IV is that the frame is bolted together through the structural members. It has been brought up by various reviewers of the design that that is an incorrect method of bolting tubing together. Further research confirms this as not being structurally sound for designs that must be fully tensioned due to the flexibility of the walls. It does appear that it can be used for solely shear connections where the bolt is chosen appropriately for the load. If this method cannot be avoided, there are specialized bolts that can be used or an insert tube must be welded inside the
References
