Motor controller for 775 dc motor

Other Hardware Motors, Mechanics, Power and CNC
1

TL;DR
I need advice for finding a motor controller that would work with a 775 dc motor

Hi,

Im making a rc tank and have ordered two 775 dc motors for driving the tracks, but im having bad luck finding a sutible motor controller. The specifications for the exact motor that im using is a bit lacking, so where im missing numbers I use the worst case that i have found for the same kind of motor.

Worst-case meassurements that I will use:
Torque: 300g cm
Stall current: 50 amps

The tank will be controlled by a Raspberry Pi running arduino IDE, and will mostly run on flat ground, but I would like to climb some hills too. The tank will weigh about 10 kg. The circumference of the tracks are ~900mm with 96 links on each side with the driving gear having 10 teeth. The power from the motor will go through a 20:1 gearbox before going to the drive gear. From what I have read the absolute minimum torque of a 775 motor is 300g cm, and using some rough calculations I found that 20:1 should work just fine.

The required specifications for the motor controllers are:
3-6s LiPo (I would be fine with 3s, but something that can handle 6s would be nice in case I decide I would like more speed)
At least 20a (I have read that most 775 motors have a stall current of 40-50 amps, but I can't see the motor ever drawing more than ~10-15 amps when running normally so what I think would work would be using a 20 amp motor controller and 20 amp fuse in case the motor ever stalls. Again something that can straight up handle the 50 amps would be nice)
Bidirectional
Brushed
Controllable by a Raspberry Pi (PWM, I2C, etc.)
Not too large (Max like 150x100mm each, but preferably smaller)

When it comes to shipping I live in Norway so delivery times kinda suck unless its from somewhere in Europe, but as long as the delivery time isn't too long (like not longer than like the middle of february) it should be fine. Also the controllers can't be stupid expensive ofc.

I have found two potential controllers:
High Power 2000W 40A Forward and Reverse Motor Speed Controller PWM Brush Motor Controller DC 12V 24V 36V
PWM Speed Regulator, Continuous Current PWM Motor Speed Regulator, High Precision Voltage Control DC 12V 24V 36V 50V

The second one is only one direction, but I have read that you can switch the polarity of the with relays or a DPDT switch, however im not an expert on electronics so I would require some assistance if I were to go that road.

If you need any more information please go ahead and ask an I will respond as fast as I can.

Cheers!

2

The first driver looks like preferable unless You will sit on the tank turning the knob.

3

I bought two of these BTS7960 43A High Power Motor Driver Module/Smart Car Driver Module for Arduino but won't be trying them for another few months. Fairly new to the market. Seem like they will be great.

I have been using one of these ( Cytron SmartDriveDuo-30 Motor Driver 2 Channels 30Amp 7V-35V DC) and it works well but it may not have enough amperage for you. You can buy more powerful ones.

4

Brushed DC motors briefly draw the stall current every time they start moving, so the controller either needs to comfortably handle the full 50A, or to actively limit the current to a lower value, to produce a "soft start".

5

@jhaytera
I have read the reviews for the first one and it looks like it can't really handle the full 43 amps and quite a few have had problems with bent pins during shipping. The second one however could work fine, though its kinda expensive so ill continue looking for alternatives for a bit more before deciding.

6

@jremington
Would it draw less amps just by starting at a lower speed or is it done some other way? I plan gradually accelarating either way to reduce the wear on the gears.

7

No. The start/stall current is determined by the motor power supply voltage and the winding resistance.

8

@jremington
Right, how would I limit the current at the start then? The first of the two controllers says it has a limit of 40a and rated at 20a continuous.

9

Your only options are to buy a current limiting motor driver (example), or a motor driver that can easily handle 50 Amperes.

10

@jremington
Could I add a current limiting circut between the motor and the controller? Also would it be possible that the controller can just straight up handle the current spike since its soo short?

11

You can fiddle around and learn from your failures, or buy equipment that is professionally designed for the task, and actually works.

Another alternative is to buy less powerful motors, and use cheaper drivers. But they still have to handle the start/stall current.

12

Yeah I guess thats an option too. I will see what I end up doing.

13

The 43Amp rating of that BTS7960 motor driver comes from the internal 43Amp current limitation at 25C of the motor driver chip (see the graph in the chip's datasheet).
Leo..

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