Speed Calculator

[SpEEdyBL]

It may be necessary to consider rpm drop of the motor under a load in the calculations.

RPM drop of the motor (per amp) is the unloaded kv x the resistance. Rpm drop will always be the same no matter what voltage. Ex. a 5000 kv motor with .006 ohms will drop by 30 rpm per amp. So if you're running it at 7 volts and it's drawing 20 amps, it will have 34400 rpm. At 1 volt and 20 amps, it will have 4400 rpm.

[BrianG]

Originally Posted by SpEEdyBL

It may be necessary to consider rpm drop of the motor under a load in the calculations.

RPM drop of the motor (per amp) is the unloaded kv x the resistance. Rpm drop will always be the same no matter what voltage. Ex. a 5000 kv motor with .006 ohms will drop by 30 rpm per amp. So if you're running it at 7 volts and it's drawing 20 amps, it will have 34400 rpm. At 1 volt and 20 amps, it will have 4400 rpm.

That's nice to know, except many motors don't specify the resistance, and you don't really know the current it is pulling unless you simply use worst case numbers. You can't generalize either because the current draw depends on too many factors. I'll see if I can add that, but not make it required so the calculation will still work if current and resistance are not available.

Anything else to add to make the script more accurate?

[BrianG]

OK, yet another update to add the feature SpEEdyBL mentioned. At this rate it will be accurate enough to be exact! (OK, maybe not):

http://www.scriptasylum.com/rc_speed.html