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I have purchased x4 612 RPM actobotics motors. Every time I try to drive the motors on ground, the motors stall, as if the torque was too low to drive.

The motor model: servocity.com model #: 638284 Planetary Gear Motor 612 RPM @ 12v (1/14 Ratio)

Here is a picture of how i assembled the motors to the chassis:

Agent 390 motor assembly (modified to fit 4 612 RPM motors)

See: Original Agent 390 chassis motor assembly

I have looked at the motor torque tables on this specific model. I have calculated that if my robot weighs 15lbs, that with x4 612 RPM motors, they should be able to run at about 500 RPM:

I weighed my robot and it only weighs 12 lbs, but the motors are too weak to drive!

What I want to know, is: what should the RPM of four 612 RPM actobotics motors with 12 lbs on them collectively, being powered by an 11.5v, 3000mA battery pack be?

And... should the motors be able to hold a 12 lb load?

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    $\begingroup$ is the battery pack actually delivering 3 A? .... what do you mean by hold a load? $\endgroup$
    – jsotola
    Jul 4, 2020 at 2:26
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    $\begingroup$ A picture of your setup and the exact motor model numbers would be helpful. $\endgroup$
    – DrMrstheMonarch
    Jul 4, 2020 at 10:37
  • $\begingroup$ The information from amazon.com says so. But not 100% sure: (I tried to test the amps with my multimeter, and almost shorted the battery!). And as for "hold a load", im talking about 12lbs @jsotola $\endgroup$
    – X Builder
    Jul 4, 2020 at 20:33
  • $\begingroup$ why are you putting important information into comments? ... it belongs in the question above, not in comments $\endgroup$
    – jsotola
    Jul 5, 2020 at 5:56

2 Answers 2

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The no load current draw, per motor, is 0.52 amps. You have 4 motors, so you're looking at over 2 amps for no load.

The stall current is TWENTY amps, per motor.

You also appear to not be using an actual battery, but rather some portable power device that has an internal battery. The electronics in it could easily be performing a short circuit detection and killing output to safeguard the battery.

You should check current draw with your multimeter:

  1. Make sure the multimeter probes are plugged into the current ("A") connectors, then
  2. Make sure the multimeter is set to current, then
  3. Attach the positive lead from your battery device to the positive port/probe on the multimeter, then
  4. Attach the negative lead from the multimeter to the positive connector on your robot.

You measure current with a multimeter by putting it in series with the load. Putting it between the battery and load will let you measure the total current output of the battery.

I would guess you'll see one of two things:

  1. Some small power draw for your electronics, then a rise in current when you try to run the motors, but to an amount not sufficient to run them, like 1 or 1.5 amps, for example, or
  2. Some small power draw for your electronics, then suddenly no current at all when you try to run the motors, which would be a short circuit protection disconnecting the power output.

You'll either need more battery packs or you'll need to ditch the portable electronics and use the batteries directly (or both!)

Lastly, your four motors have the potential to draw a combined EIGHTY AMPS of current. I would strongly suggest you check the current limits of the wire gauge you're using, pick a value LESS than that, and add a fuse so you don't start a fire.

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  • $\begingroup$ Ok. What AWG do you suggest i use? @Chuck $\endgroup$
    – X Builder
    Jul 8, 2020 at 1:35
  • $\begingroup$ As for testing the current, I don't know how to do that without shorting the battery @Chuck $\endgroup$
    – X Builder
    Jul 8, 2020 at 2:08
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    $\begingroup$ @SamuelWalker - You put the multimeter between the battery and the circuit - in series with the circuit. Multimeter in parallel is how you read voltage, multimeter in series is how you read current. As long as there's some other load connected (i.e., your robot) you won't short the battery. For the wire, you can use whatever gauge you want, but you should fuse the circuit if it's not rated for at least 80 amps. I doubt you would (or even could) run wiring rated for 80 amps on a robot that small. $\endgroup$
    – Chuck ♦
    Jul 8, 2020 at 13:22
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Without the exact circuit its difficult to be sure. If connections are properly done, most probably the power source(battery pack in this case) is unable to provide sufficient current to power the motors. A good start would be to connect just 1 motor and check if the battery pack is able to run your motor. You can also try a different power source to confirm.

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