Verifying safe motor control and gear motor compatibility?

I currently have a Raspberry Pi 3 Model B V1.2 © Raspberry Pi 2015 and want to drive one motorized wheel. I’m unsure what motor controller and gearmotor combination is safe to use together. I’d rather use a slightly undersized gearmotor than risk burning out a motor controller.

Q1: In general, what rules-of-thumb should I follow when selecting a speed controller / gearmotor combination?

Q2: The Dual TB9051FTG Motor Driver delivers continuous 2.6 A (5 A peak) per motor. Is it safe to use 6V Low Power 2.4 A stall current 25D metal gearmotors such as the 20.4:1 Metal Gearmotor 25Dx50L mm LP 6V? ie: If the gearmotor encounters a stalling load at 2.4 A and the motor controller has a 5 A peak rating, will the motor stall first and protect the speed controller?

Q3: Since I’m only running one motor, could I move up to 6V High Power metal gearmotors with 6.5 A stall current and connect a more powerful gearmotor to BOTH motor outputs? If so, how do I wire that connection? Do I run red wires from both positive outputs to the same motor input and both neg outputs to the other motor input? (I think this is parallel wiring?) Or, do I run output A’s positive to one motor input, output B’s negative to the other motor input, and bridge output A’s neg to output B’s positive? (Is this wiring in series?)

Thank you for any feedback or suggestions!

Hello, John.

1.To be safe, we generally recommend choosing a motor driver that has a continuous current output equal to or greater than the stall current of the motor you want to use, though depending on how you drive the motor and what precautions you implement in your system, you can get away with less.

2.That LP 20:4:1 25D gearmotor should be fine with the TB9051FTG. Please note, stalling a motor like that can cause them to fail quickly, which could cause shorts and result in further damage to your system. In general, we recommend running our motors at about 25% of their stall ratings.

“If the gearmotor encounters a stalling load at 2.4 A and the motor controller has a 5 A peak rating, will the motor stall first and protect the speed controller?”

This is a weirdly worded question. If the motor is powered with 6V, it will draw 2.4A as a consequence of being physically stalled. The motor does not become stalled because a certain current was drawn.

3.Unless the datasheet for a motor driver specifically mentions paralleling two motor channels (which the TB9051FTG does not), we do not recommend paralleling the outputs. Different tolerances in timing between the two channels can lead to shoot-through (both the upper and lower FET on one side of the H-bridge being on for short periods), which basically causes a short between power and ground. Since you only need to run a single motor, you might consider our VNH5019 carrier or G2 high-power motor driver 24v13, though they are a bit overkill for that motor. If you want something to plug directly into your RPi, our dual G2 high-power motor drivers are our only higher power option.


Hello Derril,

Thank you for the very helpful response. This is why I have Pololu stickers on all laptops and toolboxes.

The extra info about paralleling two motor channels is great. I was not familiar with “shoot-through” and will check datasheets before attempting any such setup. And those other two recommendations seem much better suited to my needs. I’ll look at those in more detail.

Thanks again!

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