Talk:Car/Kinentic Vehicles Proposal

When this says "use of power cube" does that mean this will be a hydraulic drive vehicle that gets 100mpg? I remember reading that hydraulic transfer is much less efficient than mechanical, how will the loss in efficiency be made up? - Lex Berezhny 13:47, 14 February 2012 (CET)

• I think the best practical efficiency of high quality hydraulic pump/motors is 85%. The efficiency of a hydraulic-drive vehicle can be increased in the following ways:
  • Use hydraulics for pretty much everything; this saves weight. The drive, steering and suspension can all be hydraulic.
  • Build the hydraulic system so it recaptures energy from the suspension and braking activities. FedEx trucks were able to get 85mpg that way.
  • Integrate the largest, strongest hydraulic component (the accumulator) into the frame of the vehicle as a stressed member.
  • As much as possible, use metal tubes instead of rubber hoses.
  • As much as possible, use the highest quality pumps/motors possible.
  • Three wheels instead of four.
  • Aerodynamic body.
• The efficiency discussion is complicated by the fact that the GVCS is supposed to be a system of systems. To a large extent, it is the efficiency of the overall system that is important. The efficiency of any one machine is much less important. Measuring the efficiency of a vehicle as compared to other vehicles is unfair, since there are dramatic efficiency gains in terms of manufacturing and maintenance that are realized by the use of modular components. Additionally, defining the vehicle in such a way that it has no (or very few) commercial equivalents (a 3-wheel 2-seater with 1000 mile range for example) means that it's difficult (if not impossible) to compare the vehicles efficiency to anything else.
• Besides, the ultimate goal is a biomass-fueled vehicle, which means even if it's 100% efficient it's going to have a 30 gallon "tank" (or something outrageous given the low energy density of pellets) just to reach the 300 mile range that's standard for passenger vehicles.
• What I mean is: don't worry about the efficiency. There are far more important factors in the design. - Matt_Maier 14FEB2012

Lex, that's been my experience as well--hydraulic drives are ideal for low speed high force applications, such as lifting loads and moving soil, but viscous drag etc makes them less suited to high speed low force duties...such as driving a lightweight streamlined car at highway speeds. But Matt offers some interesting ideas for improvements; here are my ideas on those ideas:

• • There aren't a whole lot of accessory tasks on the OS Car (as originally proposed) and the only need for power steering or power brakes will be if the drive system gets so heavy that normal human effort is insufficient. The suspension idea is intriguing--shock absorbers are already hydraulic and are currently designed to waste energy, not conserve it--if there's enough energy there to be worth the weight of tapping it, that should be a winner.
  • Recapturing energy from braking is a proven winner, and hydraulics are (apparently) much more efficient than batteries at that task. If the car does sufficient stop-and-go driving to justify the mass of the recovery system, then it's a winner. It seems ideal for the small package express business (though an 85 mpg FedEx truck seems beyond the current state of the art).
  • Technically, using the frame as an accumulator is ideal, but in an accident, the risk might be excessive. Might be; I don't know enough about hydraulic drive. I do know that high pressure hydraulics (e.g. diesel fuel injection) pose a risk to workers diagnosing pinholes and cracks, but if frame damage only risks the passengers getting slippery, rather than getting sliced, having the chassis serve double-duty sounds like a good idea.
  • Possibly the frame would be more useful as a tube and hose substitute than as an accumulator; at the very least as a fluid return line. (sort of like how the frame is used as the negative wire back to the battery on conventional cars).
• All in all, the weight given to the other important (indeed more important) factors of the design will determine where efficiency factors rank, but there's a point when efficiency factors get low enough that there's no use bothering with the OS Car at all.

I'll try to find a place to list the trade-offs we need to consider before we start turning wrenches. For example, can someone provide a drawing of where the Power Cube goes in a streamlined two passenger three wheeled car? All my sketches end up either unstable in roll, or with worse aerodynamic drag than four wheeled variants. - JackMcCornack 18FEB2012

Technically anything can be "low speed high force" if you gear them properly :-)

• I've been collecting research on hybrid hydraulics for a while now. Hybrid_Hydraulic_System Research_Development#Design
• My mistake. It was a UPS truck. EPA Hybrid Hydraulic Program presentation on HHV's
• One of the reasons active hydraulic suspensions weren't popular in car racing was the danger of getting sprayed by 3000psi hot oil. At that pressure it gets injected straight into your body; right through the skin. Kind of dangerous.
• I figured the power cube(s) would go in between the front wheels, the passengers behind them, and then a single rear wheel. The ones we have now are kind of bulky, tho. A 2 foot cube is hard to fit anywhere. But that's probably okay; I figure we'll need a new power cube model for a passenger vehicle anyway. Getting up to 70mph will probably require a redesign for significantly higher flow if not for additional reasons.