[seanalltogether]

The drivetrain and steering assembly have definitely been designed to make it cheaper to build and easier to maintain which I think is a good thing. I wonder how much more expensive and complicated it becomes to have 4WD.

[hanniabu]

My guess is that accounts for about 30% of the costs.

[neogodless]

The existing Rig is $4750 USD and is rear-wheel-drive only. Are you saying it would cost 30% more to make it 4WD?

[Someone1234]

Given that the electric monitor is in-line, and there's no gearing or shaft, I mean is that such a stretch? The easiest way to make it 4WD would be a second electric motor, which could easily be 30%.

[Someone]

Driving the front wheels is more complicated because the front axis is used for steering (it might be easier to go for two motors there, and, if you go there, 4 identical motors might be the better choice for maintenance/repairability).

I think you also would need to guarantee that both engines are aiming for (about) the same speed, even in corners or when tire pressure changes. That might require something technically similar to ABS.

Also, does this have a differential on the back axis? I couldn’t spot it, but that may be because I don’t know what they can look like on these relatively low-powered devices.

[mlyle]

> I think you also would need to guarantee that both engines are aiming for (about) the same speed, even in corners or when tire pressure changes. That might require something technically similar to ABS.

Equal torque is good enough. They'll settle to speeds consistent with turning, etc.

Since they're independent motors, you don't need to worry about the case where a wheel is spinning stealing all of the torque.

> Also, does this have a differential on the back axis? I couldn’t spot it, but that may be because I don’t know what they can look like on these relatively low-powered devices.

I don't see it. Often ATV, etc don't have them: you get enough wheel slip on low traction surfaces that turning works fine, and the prospect of one wheel with impaired traction stealing all the torque is bad.

There's those Russian sidecar bikes.. they have just a clutch for the second rear wheel. If you're on a paved surface, you use one driven wheel, but if you're offroad and could use 2WD, you can engage the clutch (and slippage does the job of a differential).

[michaelt]

> Equal torque is good enough.

Eh, you'll still want to redistribute torque if you're planning to accelerate hard. After all, accelerating shifts weight onto the rear wheels, giving them more traction and the front less.

Front wheel skids aren't acceptable as you use them to steer. And limiting your rear wheels to the amount of torque that would make the front wheels slip means you're leaving a fair bit of performance on the table. And presumably getting more performance is the whole point of going 4wd!

[shoes_for_thee]

The motor does appear to drive the rear with a chain drive

https://notawheelchair.com/wp-content/uploads/2020/06/202001...

Not sure what a good way to run power to the front of it would be esp given the steering system and two front axels