Sunday, March 30, 2008

Entstort Motor Testing at Mike's

Today I dropped by Mike Senna's house to start our testing of the Entstort motors, which are potential replacements for the Trico wiper motors.

The first thing we did was measure the RPMs. At 12 volts, the Entstort motors ran at about 36 RPM, and at 24 volts they ran at almost double that, 76 RPM. The Trico motors run at about 88 RPM with 24 volts applied, so the Entstort motors are about 15% slower.

Of greater concern was the current draw. The Entstort motors draw about 1.5 amps under no load, while the Trico motors draw less than half that, about 0.6 amps with no load. This is bad news for battery life.

Curious as to why the Entstort motors draw more current, Mike theorized that the brushes and magnets might be different. We opened up both the Trico and Entstort motors, and they were actually quite similar in windings, brushes, and magnets.

Later, Mike measured the motor resistance, and found that the Entstort motors measured a resistance of 3.7 ohms, while the Trico motors' resistance measured only 1.8 ohms. Mike suspects more windings are present in the Entstort motors.

We decided to open up the gear area of the Entstort motor to see how similar it was to the Trico motor. This required a Dremel to hack off the rivet heads.

The Entstort motors look pretty similar to the Trico motors. A steel worm gear meshes with a nylon wheel to turn the shaft.

When I got home I took a picture of the emptied motors side by side, and I tried swapping the nylon gears to see if they would fit in both motors.

It turns out the nylon wheel in the Trico motor is just slightly larger than that of the Entstort motor, and it doesn't quite fit in the Entstort motor. Likewise, the Entstort wheel is a little too small in the Trico motor, and wiggles slightly in the Trico housing.

It looks like we cannot cannibalize these different motors for part swaps. Also, the worm gear on the Entstort motor doesn't appear to be quite as beefy as that of the Trico motor, especially in the base area.

The Entstort motors have not yet been tested under a droid load yet. I may get to that someday, but not right now.

The preliminary conclusion is that while the Entstort motors probably supply stronger torque, they do not appear to be quite on par with the Trico motors in most respects (power usage, RPM, potential worm gear failure). In a pinch, they may have to step in, if the supply of Trico motors has really dried up.

It's time to start trying to contact Trico to find out the what the real story is on their motor availability.

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