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DC motor test


Just wanted to know, if any of you know a good way to test DC motors?

I need to test my motors for: Max and min. speed, current with no load, current with heavy load and stall current.

When i measure the motors resistor, i get about 3ohm. Then i tried to calculate 4.5V / 3 = 1.5Amp. But if i am correct hose motors have a stall current on about 2.7Amp. Did i calculate it wrong?

The 2 motors i need to test, are those from the LMR Mr. Basic.

Not sure how to do those test.

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The current is measured with your multi meter in the Current/Ampere setting. Make sure your meter can handle a few Ampere (a few thousand milli Ampere!). You might need to change the probes' connections.

Then hook up your meter in series with the motor and the power source. So:
Battery(+) -> meter(+) [meter] meter(-) -> motor -> Battery(-).

Now run the motor while the wheel is free in the air, read the meter. That is your free running, "no load" current.
Then run the motor while you let the wheel rub against your finger. Now you're measuring the current "under load". More friction is more load is more current.
Finally hold the wheel still while the motor is still powered. This is called "stalling" the motor. Read the "stall" current.

In order to measure the speed of your motor, you need a way to count the rotations of the wheel. I've never tried that. The only speed I know for sure is the stall speed: 0 Revolutions Per Minute (RPM).

NICE! thanks for the respond :0)

Will try it tomorrow.

Hmm maybe if i just put power on my motors while they are mounted in the chassie, and then try and see how long it will take for it to drive 1m, then i should be able to calculate the speed.

Just 1 problem, they dont run with the same speed, so will be hard to get it to drive in a straight line.

If you make your robot navigate via infrared etc towards something, it should correct itself. Otherwise, check if there are dig hairs or something wrapped around the motor shaft. Sometimes you need to mess with a couple motors to get them to go in sync.

My robot is not finish yet. cant get it to drive. Might be my software that is not working correct, think it is the PWM section :0(

So i where thinking on just adding power to the motors without any other electronics involved.

What do you mean about "mess" with the motor, is there any ting i can do to get them to drive with same speed?

Ooof. The drive system in Mr Basic is notorious. There is a lot of friction in all the parts. The left side of the vehicle will never experience the same level of friction as the right part.

Try to adjust the distance between gears. You can slide the pinions (smallest gears) over the shaft. Half a millimetre at the time. Try to find the transmissions (from gear to gear) where teeth are "touching too hard". See if you can relieve some of that tension. Perhaps the wheels are too close on the axles. They can be adjusted by tightening/loosening the nuts on the treads.

Oh and never forget the MythBuster's shop motto: when in doubt, use more lubrication! I used Vaseline, Petroleum Jelly. (The MythBusters have a similar motto that I would use as the very last resort: C4.)