Motor RPM findings

[neurokinetik]

Well, I've started to use the oscilloscope to measure motor RPMs. The most surprising thing so far, is that the stock motors so far seem to actually perform pretty close to their advertised specs. The modified motors are proving to be difficult, if not impossible to measure because they generate much more noise in the scope reading.

Anyway, the three stock motors I've measured so far:

Good Stage 1: 26087 RPM
Good Stage 2: 30000 RPM
Average stage 2: 28571 RPM

More to come...

[TypeZer0]

i see you're enjoying your new oscilloscope that's good to hear because if i remember right, namuna did some rpm tests on zipzap and bitcharg motors and most of them didn't live up to their advertised speed and it didn't matter whether they were the low current drain slow motors or the really fast ones. what i really wanna see are the results of your custom motors, from your best 130 to your favorite 180. thanks for the info and keep us updated! oh yeah, may i suggest you keep links of your own threads like the motor current draw thread or advancing the timing thread in your signature so when people ask, you can be like "just check out the links in my sig"

[aperson]

thats not too bad.

The modified motors are proving to be difficult, if not impossible to measure because they generate much more noise in the scope reading.

how does noise effect the scope reading?
IDK what an oscilloscope is.

[Schr-eng]

Is there any way you can capture the data on your scope and save it to your comp and then post a link to it? It would be nice to see some raw data.

Also, have you tried giving the motor a load so you can get some torque figures? That kind of info would be most helpful.

[neurokinetik]

Originally posted by aperson
how does noise effect the scope reading?
IDK what an oscilloscope is.

The most basic description of an oscilloscope is that it is a voltmeter that graphs voltage over a period of time.

I found this link, which told me exactly how to go about measuring the RPM on the scope. We all know that these motors generate electrical noise. It is that noise that interferes with out radio signals. The capacitors that are soldered to the motor can help suppress that noise, but some still exists.

This link shows exactly what I am talking about:

http://www.solarbotics.net/starting/..._dcmotor3.html

The problem with the highly modded 130 motors is that the waveform doesn't appear as clean as what you see in that pic. It is such a mess that the scope has a hard time locking onto it, and then I can't get a measurement.

Anyway, I tried the 180 motors, which all gave a clean signal.

Team Orion Stock: 16216 RPM
35 turn (28 Ga) 180 motor: 23077 RPM
GPM Modified 180 (35 turn): 17647 RPM
30 turn (26 Ga) 180 motor: 28571 RPM

The other thing I started to do is to try to validate my readings, by cross-referencing them with the Tamiya Speed checker measurements.

Here is what I found:

S1 drift: 13.3mph (from RPM measurement) 11.8mph (from Tamiya Speed Checker) difference: 11%
S2 drift: 12.1mph (RPM) 10.5mph (TSC) 13%
S2 drag: 16.4mph (RPM) 13mph (TSC) 21%
GPM Mod motor: 12.9mph (RPM) 11.2mph (TSC) 13%
30 turn 180: 20.8mph (RPM) 18.6mph (TSC) 11%
Team Orion: 11.8mph (RPM) 10.5mph (TSC) 11%

So other than the S2 drag motor, my measurements are all pretty consistent. That is a good sign.

Oh, and if the Tamiya Speed Checker was known to be 100% accurate (and it isn't) then we'd be able to conclude that the XMods have around 12% drivetrain loss, and that is with AWD.