Wow, that is pushing the envelope. I don't see a downside except for leaks? But current systems have plenty of failure points as well. I would LOVE to someday have a silent side by side to go exploring the forest. Each wheel individually controlled with tons of torque and a soft ride.
hmm, i wonder about using the system in mud and snow. if one wheel loses traction; then does it spin fast and the other wheels lose power? same question with extreme valleys and bumps that make one or more wheels lose traction, such as Moab rock climbing.
amazed W1
Once again the competition in drives between electrics and hydraulics. In the past the electrics have always won, but the locked rotor or runaway rotor problem is easier to deal with by hydraulics? Also the overall efficiency, i.c. motor to wheels looks better, so guessing, the electrical version is better for battery sourced vehicles with a good recharging grid but the hydraulic version is better where the range needs to be much greater, as in the deserts of OZ.
200-1500 psi isn't much compared to regular hydraulics, but things will still get interesting if there are any leaks or dings.
We've had this kind of drive in agricultural equipment since 5the 50's. It has some serious advantages, but also disadvantages (like leaks).
Koko The Talking Ape
I have some questions. Like others, I wonder how pressure will be distributed to the various wheels to control traction, etc. I believe both ICE and electric motor vehicles use mechanical clutches, which work pretty well. Electric hub motors are heavy, as the article points out, but they allow fly-by-wire control of each motor, even when used for regenerative braking. The devices that allow that are solid-state (I believe) and hence super-reliable, and easily controlled by the car computer.
Second, I wonder if the pump will always be able to maintain pressure under momentary high loads. In an electric car, lithium batteries maintain "pressure" (voltage) fairly steadily until they are depleted. The same is true, in effect, for ICE.
Third, I wonder how well the hydraulic motors stall. If the wheels simply can't turn, there should be some kind of valve or throttle so that pressure doesn't build uncontrollably. That would be another mechanical component that could fail.
I also wonder about "gears." Like propellors or wind turbines, I imagine these hydraulic motors are most efficient at a certain rotational speed. What if you need different speed? Is there friction? Turbulence? Cavitation? Does the fluid heat up? The fluid might heat up, and in fact the pump might have to work harder, non-intuitively, like when the vehicle is cruising at low speed, or at high speed.
As a side note, it occurs to me that this kind of rocker suspension (I have also heard it called a "bogie" suspension) prevents squat or lift when the vehicle accelerates, because torque around each hub is cancelled out. Also, the rocker arm may have to pivot exactly between the two wheel hubs, or else the rocker arm would tilt one way or the other under acceleration, because of unbalanced torque.
It also occurs to me that you could tiny hydraulic motors inside the joints of the arms, to help counter the torque effects from the hub motors.
Two wheel drive motorcycles?
If the weight advantages really are there, and design intent could factor in other means to achieve it (such as material selection), could this tech find application in aviation? It seems like it could really be effective in distributing the weight desirably: allowing a centrally located power unit to "feed" remote motor/propeller units. The tech should also allow these units to pivot easily, making VTOL and multi-copter like flight achievable, assuming the individual motors could be independently controlled effectively to maintain the needed in-flight balance. Very cool proto, tho!
I'm with Plaw, 2wd motorcycles! Both front and rear driven by this, with no chains for drive shafts. That could make for a sweet bike.
Really it would be pretty amazing on a ton of different vehicles. Offroading without a drive shaft, diffs, axles, you'd have clearance for days allowing the vehicle body to sit lower. I hope this goes places.
It's funny they never mention "hydrostatic drive" in the story, I wonder why that is. Probably because hydrostatic drive is known to be highly inefficient for power transmission. They may be able to fudge numbers to "prove" 98% efficiency at the pump, but there's a lot of friction in the hoses that they seem to be curiously silent about. Hydrostatic is excellent for low speed (low flow) drives for machines like tractors, and best of all at zero speed (starting) torque. Any application that requires high flow rate suffers crippling inefficiency that just kills the performance. I wouldn't make any production units - customers will be disappointed.