Let's Make Robots!

4 wheels with 180 degrees turning

I saw a future concept car on a presentation on a documentary on Discovery Channel.

It had 4 motorized wheels, One in each corner (like a conventional car). But each wheel could turn 180.

It would mean that your car could drive in any direction, and rotate on the spot. Here's a link to a similar concept

It struck me that that would be nice to make with four GM10s mounted on four servos. One servo in each corner, and a wheel on each GM10. But then it struck me, WHY? OK, you would get sideways mobility, but that's the only advantage over the StartHere-design, or tracks. It might be cheaper than meccanum wheels, but the amount of coding to get it rolling glitch free seems staggering.

These are my first thoughts on the subject, what do you think?

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Four wheel drive using electric drive has been done a few times, there are a number of research robots and indeed a number of security/transporter robots which use the arrangment. The syncronisation of the motors is not a major problem electric motor motors are compliant, RPM and Load is easy with these motors.

 Years ago Leyland did a 4 wheel drive Mini Moke by just fitting another engine in the back, it was reported to be interesting to drive as they had syncronisation issues and throttle sticking, the Army decided not to proceed with them.

The control laws are complex,  for example in Cars the steering is an interesting problem because what you need to do at low speed is different to that at high speed, at low speed the rear wheels may turn to the outside (i.e. turning left, front wheels turn to the left rear to the right) at high speed this is unstable as anyone who have driven a forklift will attest.

Maybe this is of interest to you:

http://www.nana.schumacher.net/robocup/technical.htm

It has won the last two years of DTU Robocup.

I believe the manuevering method described is called synchro drive, and there is even a Youtube video of a Lego version, though it has all the turning mechanisms geared together.

It is useful with maintaining facing an object directly while manuevering around it, if the wheels are independantly turnable. 

In a robot that method is fine but I'm suprised they would try it in a car. Even if they could maintain perfect wheel alignment for highway driving it is still a maintenance nightmare.
Yeah. The friction caused by one of the wheels turning only fractionally slower than the others, would cause unstabillity and would wear out a tire in a month on a car in normal use.

It gives sideways mobility and a bunch of efficiency. Tracks have very big friction and StartHere design would be silly or inefficent for cars.

 

But if you build robot what weighs less than 200kg fiction doesn't mean much.