What motor driver / shield / circuit for 540 brushed motor control on 7.2V?

I need to control a brushed 540 motor (80 turn) with forward, reverse and brake control. I'll be using a 6-cell NiMH battery at a nominal 7.2V. I tried a proof-of-concept using the ubiquitous L298N motor driver (fwd / rev but no brake yet) and it worked perfectly except for losing 2v at the motor, which I understand is quite normal for the L298N. That's too much voltage drop for my application (a 1:14 scale Tamiya RC truck) and I don't want to have to increase the supply voltage if I can help it.

I know a basic RC car speed controller will handle the job perfectly but I want to be able to set up my own throttle / brake / reverse profiles and car speed controllers have their own special way of doing brake and reverse. I'm assuming it won't be possible (or easy) to reverse engineer a basic car speedo just to use its bridge (or whatever else it uses) unless someone has already done this and can point me in the right direction.

I can't find any specs for nominal / stall current on my 80T motor. I'm wondering if I might have to set one up on the workbench to measure it. I know low-turn RC motors can pull lots of current but these 80T motors tend to run all day on a 3000mAh battery. I wouldn't even like to guess at the current draw - in the RC car world, virtually everything is quoted in turns rather than amps so I don't even know the nominal and peak limits of my basic RC car speedos (of which I have more than a few).

Is there a motor driver or shield available which can handle the kind of current I need without affecting motor voltage? I'll need to be able to control motor speed in both directions and perform braking too.

Failing that, I guess I will have to build my own FET bridge - I'm not educated in electronics and it might be a steep learning curve, can anyone point me to a suitable schematic and can anyone advise what components I would need to handle the necessary current?

Please let me know if anything needs clarifying.

Any other hints / advice gratefully received :slight_smile:

You need to know the stall current of the motor. They come with different windings. My guess is that the stall current is somewhere like 20 amps and you should use a motor driver that can handle that or which has over-current or short-circuit protection.

If you are buying a driver that cannot handle the stall current then make sure it can handle 50% to 100% more than the full load running current.

Another option is an Electronic Speed Control (ESC) that appears to the Arduino to be a servo. Be aware that many of them do not have a reverse function as they are intended for model aircraft. The Hobby King website has a good selection.


Many thanks for the advice @Robin2. Actually despite me saying I wouldn't use an RC ESC because of its internal braking profile, I was playing yesterday with a crawler ESC that might well do exactly what I want if I rethink how I want my throttle profile to work slightly.

Just waiting for January's budget to open and I'll get one ordered and start playing :slight_smile: