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BEAM Pieces is a BEAM Reference Library site.
Gearmotor test procedure
How I did what I did
After seeing my gearmotor comparison page, a number of folks have expressed interest in testing their own motors. This page summarizes the gear and procedure I use to produce my test results.
I use the following equipment:
- A variable-voltage power supply (0 - 5V is all I use,
something pretty cheap will work fine for this; my power
supply cost me $25 US)
- A voltmeter, with fairly accurate 0.5 V markings (or
a multimeter would be good here too)
- A multimeter, set to measure current (this is where
you want a meter with some serious resolution --
preferably digital)
- A wristwatch with chronometer function (or you could
use a stopwatch)
- A big sheet of paper, and pencil
So, start out by connecting the power supply and meters to the motor you'll be testing. If the motor output doesn't provide good visual cues (w.r.t. rotational position), I put a small wire clamp or piece of masking tape on the shaft.
Starting with your power supply turned down to 0 V, *slooooowwwwwlly* ramp up the voltage until the motor starts moving. For better motors, this'll be so low that the voltmeter hasn't moved off the "0" pin. For less-efficient motors, I try to take at least a couple of current & voltage measurements before the motor starts moving (say, every 0.5 V). If the "starting" voltage is measureable, make sure to measure and record the maximum current (i.e., just before the motor starts to move), and minimum running current (just after the motor starts to move). Again, this requires you to very slowly increase the voltage (keeping your eye on the current), until you see the sharp drop in current.
Things get pretty routine from here on. Measure the rotational speed at the starting voltage by timing a number of successive rotations (normally I time 10 revs, sometimes 5 for really slow motors, or 20 for really fast ones).
Then ramp up the voltage to the next 0.5V step. Measure and record current and speed.
Depending on the motor's voltage range, I then take measurements either every 1.0 V, or every 0.5 V (for motors with more-limited voltage ranges).
After writing all this stuff down, I type it into a spreadsheet to do my math for me. Here are the columns I use for inputs:
Voltage Current Time (sec) # Revs
Then the columns for outputs are
Speed (deg / sec) Efficiency (deg / mW-sec)
Note that my metric of efficiency is just the rotational speed (in deg/sec) divided by the current in mA and voltage (i.e., w / (I*V)). Speed (in deg / sec) is just (360 * #Revs / Time).
I have the spreadsheet set up to do the plots for me too, so the data collection is by far the most time-consuming part of this process.
Good luck, and feel free to send me your results for inclusion here!
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