Questions on 4wd, 1 motor per wheel

Hi there, I am considering a building for a slow moving EV and have a couple questions if someone doesn't mind.

Background
- I want to use brushed DC motors to drive each wheel separately for a simple drivetrain. Probably a geared motor stepping down again with chain and sprockets.
- Tank style steering
- I expect my wheel base to be quite big - 2m wide, but vehicle only 1.5m front to back
- To keep cost low I am thinking a rigid frame
- It is to be remotely controlled - no operator on the vehicle
- The intended use case is usually fairly flat ground with occasional awkward drains to pass through on an angle which means one wheel would go off the ground which leads to my questions.

Questions
- Can I use a 2 channel motor controller to drive 4 same sized brushed motors successfully? I.e. Just wire up left both left side to output and they should get equal current.
Following on:
- What happens if one wheel lifts off the ground? Is it as I expect - wheel of the ground will spin freely, and load double on the remaining wheel?
- Are there any examples of these types of vehicles about?

bboughton said:

Questions
- Can I use a 2 channel motor controller to drive 4 same sized brushed motors successfully? I.e. Just wire up left both left side to output and they should get equal current.

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THat depends on the controller. If it's like a powerchair controller, then they are fully independent output stages, with one control input.

Following on:
- What happens if one wheel lifts off the ground? Is it as I expect - wheel of the ground will spin freely, and load double on the remaining wheel?

Click to expand...

Again, depends on the controller. If they're fully independent, then yes. Otherwise, it depends on how that particular controller works with it's load.

If you simply use completely separate controllers on each motor, you're "guaranteed" that kind of operation.

You can even build a comparator circuit (or use a program in an MCU, like arduino, etc) to detect that the wheels are at significantly different RPM, which shouldn't happen if they're all on the ground, and have it shutoff the motor that's spinning too fast.

- Are there any examples of these types of vehicles about?

Click to expand...

The most likely place is in various types of robotics. Robot wars / battle bots, or any of the high school or college or other robotics programs, as well as likely a lot of people's web pages that are just building their own stuff...but I don't know what to search for, other than something like "quad all wheel drive / AWD / 4WD robot".

There've been at least one thread around here about people using hubmotors (usually BLDC) in a quad AWD robot, at least one for a robot-wars type thing.
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Great. Thanks I'll do a little more digging. I built a smaller rover a few years ago with a sabertooth 2 channel controller. I will probably experiment with that first. The comparator circuit sounds interesting.

If the motors on one side are wired in parallel, having one wheel lose traction won't keep the other one from driving. This would be the simplest approach.