If the DPDT switch is used on the output to reverse the motors, to keep the outputs isolated you would need a 4-pole double throw switch on the outputs. Alternatively, if you don't need centre off, you could do the same thing to the output as Brian suggested for the potentiometer switch and use a single pole switch (or one pole of the existing switch) to control a pair of DPDT relays.

Brian (another one)

Can you provide details of the controller model?
The more advanced conntrollers actually use a 0-5V (or similar) control voltage which is generated by a potentiometer a 5V supply. If thi is the case you could use a single pot with 3 connections (common, 5V and variable) to one controller and two (common and variable) to the other. If they are cheap ones using a RC circuit then you will need a dual potentiometer. Make sure that it is linear NOT log or "audio" taper. The matching between sections would normally be better than 5%.

https://uk.rs-online.com/web/p/potentiometers/1638384/

Rober G8RPI

If you need better "balance" you might consider using a couple of PWM ports on an Arduino. With care I would think you should be able to get sub 1% balance.and a whole heap more functionality should you need it.

It might be possible to connect the two together electrically, but as we don't know the controller circuitry doing so is downright risky. I'm with Stuart. Get a dual potentiometer and a DPDT switch. Linking the controls mechanically eliminates any chance of getting into electrical poo, and it's a simple and cheap solution.

I doubt 5% difference on the pots would make much difference to the motors, and it's likely the pots will track closer than 5% anyway. If it's a problem you can buy high-tolerance components but I wouldn't bother unless you hit trouble with ordinary potentiometers like these. Amazon also do DPDT switches. Many, many other suppliers, switched double pots and DPDT are both common as muck electronic parts, and you don't need anything special to work a controller.

Dave

Now I've looked at those budget controllers I concur with SOD. Without getting them on the bench and having a poke around at the circuitry to find out exactly how the pots are connected into the gubbins it might be better to stick to two pots on a common shaft.

As these controllers are PWM devices I'm sure it could be done in the way I suggested with an Arduino but it would take a little R&D to avoid letting out any of the blue smoke.

Another option, depending on your batteries would be to use 48V and run the motors in series/parallel on one controller. Series the two motors sharing an axle and parallel the two bogies. If you series the bogies then one slipping would "take" all the voltage and you will loose power at the other bogie.

Otherwise I concur, a dual pot is the way to go. If I had a controller to hand I'm sure a simpler control could be worked out, but I don't.

To keep it mechanical you could of course make a throttle lever and gear (ot miniature toothed belt, crank etc) to the two control pots…..

Robert G8RPI.

Ron

Have you considered using two single pots and connecting the shafts with gears so that one is connected to the control knob and the other is a slave?

The advantages are:

1. you can make mechanical adjustments to reduce the difference (if any) in the two pots.
2. two single linear pots will be easier to source
3. there are plenty of cheap plastic gears around that will do the job.

John

I would advise a single controller.

In my experience potentiometers can be mismatched at the very bottom of their travel so it's quite likely that one motor will power up before the other.

One motor powered and one stopped is more likely to promote slipping than in two motors already turning. And this right at the times when you need the best control over adhesion.

Using one high-power controller will ensure both motors can balance (if one slips it will generate more back-emf diverting power to the other motor, and if one motor stalls it will 'steal' power from the other – an ideal situation).

Neil