Off Road Vehicle Has Six Wheels And Fluid Power

What has six wheels and runs on water? Azaris — a new off-road vehicle prototype from Ferox. Azaris has a rocker suspension modeled after the one on the Mars rover. The problem is, linking four drive wheels on a rocker suspension would be a nightmare. The usual solution? Motors directly in the wheels. But Ferrox has a different approach.

The vehicle has a conventional BMW motorcycle engine but instead of driving a wheel, it drives a pump. The pump moves fluid to the wheels where something similar to a water wheel around the diameter of the wheel causes rotation. The fluid is mostly water and the pressure is lower than a conventional hydraulic system. Auto Times has a video of some stills of the prototype and you can see it below. We haven’t actually seen it in motion, unfortunately.

According to media reports, the pressure runs from 200 to 1,000 PSI which is a lot lower than in a conventional system. The motorcycle engine provides 100 horsepower and could be replaced by an electric motor if desired. They also quote the motors as being 98 percent efficient, although we think that means considering the energy in the water pump’s output to the wheel’s energy, not the thermal efficiency starting with the motor, as an internal combustion engine is doing great to accomplish 50% efficiency.

The selling point is that you can drive wheels using a liquid drivetrain that is supremely flexible. This allows you to do things like the rover-style suspension that would ordinarily require heavy motors in the wheels. The liquid motors are about 24 pounds each. Equivalent electric motors could weigh up to 66 pounds. The motorcycle engine doesn’t even max out the amount of power the wheels could deliver, so there’s room to grow.

These are prototypes and not for sale at the moment, unfortunately. They are simply to showcase Ferox technology. We couldn’t help but wonder if anyone has tried a similar scheme for a robot or other hacker drivetrain?

We’ve seen water power charging a cell phone, but that’s hardly the same thing. We also saw some pretty conventional but tiny hydraulics in this model excavator. The idea is the same though. Use hydraulics to move something with a remote motor.


44 thoughts on “Off Road Vehicle Has Six Wheels And Fluid Power

    1. “The vehicle has a conventional BMW motorcycle engine but instead of driving a wheel, it drives a pump. The pump moves fluid to the wheels where something similar to a water wheel around the diameter of the wheel causes rotation. ”

      Ahem. Although I’d worry about longevity and seals.

    2. So… its not hydrostatic, and not quite hydrodynamic, but it uses non-positive displacement motors to drive the wheels? I’m seriously skeptical of the design choices here. However, looking at the pump and motor on their website, it looks like a cam actuated radial piston pump and motor, made from machined plates instead or the usual machined castings I’m used to seeing. Water wheel my ass, this is hydrostatic with fixed displacement directly proportional to engine rpm. It would increase efficiency to use variable displacement axial piston pumps or motors, which are lightweight and readily available.

  1. ‘”instead of using hydraulic fluid, the motors in the six-wheeled Azaris will be driven by 95 per cent water, with the remainder a combination of anti-corrosion, lubrication and antifreeze solution. They generally operate between 200 and 1000psi, but can push to 1500psi in high-load applications.”

    1. When I looked up “hydraulic fluid” on Wikipedia, there was a whole chapter about water based fluids, with it’s advantages (not flammable, less environmental impact in case of leakage) and drawbacks (e.g. less lubrication).

      1. Damn interesting. 60% efficiency in marine diesel engines. HCCI, didn’t know about those. The airplane engine I don’t even understand how it works. Supersonic shockwave ignition?

    1. Next time you go to a fair with the all the large show rides, have a look up at the hydraulic motor that moves those tones of steal around in the air.

      You can get massive amounts of torque out of such a small motor.

      I have often thought about this in the past. I even designed the concept of a continuously variable hydraulic pump on paper.

      You get lower unsprung weight in several ways –

      Limited slip can be done with small valves.
      No requirement for differentials.
      Traction control can be done across all four (or more) wheels as a single unit and the control can be sprung weight.
      A regenerative breaking unit can be sprung weight.
      Breaking systems can be sprung weight.
      No heavy transmission axles.
      No complex CVs on steering transmission.
      No transmission backlash.
      Instant unsprung hub locking for four wheel drive. (Simple solenoids around hypiods).

  2. Hydraulic (swashplate and turbine) motors of all sorts are common on slow equipment (mining, logging, earthmoving etc.) because it saves a huge number of direct-drive components (could you imagine the CV joints and complexity in a huge mining truck?), but is done at the expense of efficiency. If you’re losing 20 – 50% of your horsepower to fluid flow losses (not unheard of) the hydraulic fluid heats up. It really heats up – never grab hydraulic lines on big equipment if it’s been running. Now imagine what happens when that hydraulic fluid is water….

    1. Good call, I hadn’t thought about that. It will be effectively crippled after it warms up. I was thinking myself of the hydrostatic front axle option on john deere’s 3130 which was a disaster for safety, having no holding ability on slopes.

    2. I know of valves with integrated control electronics, where the design temperature was 105°C oil temp. For water you probably want to stay below 100°C, because you do not want to construct a steam engine, but you do not need to stay much below. But once I saw a fan for the cooler (radiator) for the hydraulic fluid: When we cranked it to full power, you had to fear it makes a take off – more than 500W, something like 24V and similar amps

  3. Repost due to my original comment appearing to be lost to the system:

    Their logic is a bit baffling. In the caradvice article linked in the comments they state, “You would have a battery pack, electric motor linked into a pump, and then the pump drives the fluid transmission system, which is what’s pushing around the in-wheel motors.”

    So uh… why not just put the electric motors in the wheels? Why introduce another source of loss when electric motors are already suited to drive the wheels directly? I know the answer: The often flawed desire to be “different”; regardless of logic.

    They cite a goal of 98% efficiency thanks to tight tolerances, but if that was really feasible the industry would already be there today (tight tolerances are expensive and susceptible to foreign debris). Instead an individual pump or motor accomplishes about 12% efficiency and when you pair them you get a hefty 25% loss. Ouch. At the end of the day, based on what they’re describing and photos of the drives they’re still just operating a tangential piston motor; I suspect something similar to what EZ Trac is doing for hydraulically driven front axles in trucks. The only key difference is the pistons move with the hub rather than staying stationary with the spindle.

    What I also don’t understand is why water and why at lower pressures? Lower pressures just means that it needs higher flows to achieve the same horsepower. The reason modern hydrostatic transmissions run in excess of 5000 psi is because it lets them get away with lower flow. That means smaller components and smaller hoses. You do increase loss from leak-by, but you either get loss from leak-by or you get loss from pressure drop due to high flow rates. Pick your poison.

    It gets better though, for regeneration they want to use accumulators. Since they’re using a low pressure system that means BIG accumulators. Once again, lower pressures aren’t always better… I just don’t see why they think this is the way to go. Or necessary.

      1. They are, but hydraulics aren’t exactly light either. Honestly wheel motors are a neat idea in terms of packaging and simplicity, but in terms of suspension dynamics it’s a terrible idea.

  4. Oh, are we doing this thing again where industrial designers create high quality artwork of an idea, and know just enough engineering to make it sound like the concept has a basis in reality?

    A more serious question is what are the losses incurred by a belt drive vs chain vs bevel gear? I can’t seem to find any info with actual numbers.
    The reason for this question is that it seems that moving the drive motor to the pivot of the swing arm seems like an obvious war to reduce the un-sprung mass. But that seems so obvious someone must have already evaluated this idea and determined that direct drive is worth the un-sprung mass penalty.

  5. If you want something to look real it can’t be perfect with perfect lighting and perfect curves it needs to look a bit shit. Now as for the tech being proposed well every piece of heavy construction equipment uses hydraulic moton systems so this really is nothing special and in fact, water is a terrible choice because it will heat up this is why you don’t use it for brake fluid.

  6. To be able to drive off the pavement, off-road vehicles need several characteristics: They need to have a low ground pressure, so as not to sink into soft ground, they need lot of ground clearance to not get stuck on obstacles, and they need to keep their wheels or tracks on the ground so as not to lose traction.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.