Speed Calculator

[BrianG]

lol, that works. I'm sure I have LEDs hanging around in my parts bin.

Ok, so I count the flashes for the various motors and invert that number to get the minimum rpms? Example: If I count 4 flashes, that means the motor has to spin no lower than 0.25rpm for proper ESC operation? Seems kinda low...

Thanks for your assistance!

[GriffinRU]

Originally Posted by BrianG

lol, that works. I'm sure I have LEDs hanging around in my parts bin.

Ok, so I count the flashes for the various motors and invert that number to get the minimum rpms? Example: If I count 4 flashes, that means the motor has to spin no lower than 0.25rpm for proper ESC operation? Seems kinda low...

Thanks for your assistance!

You welcome:)
You need to count only flashes from one LED, we are searching for zero-crossing. Otherwise you need to divide total number of flashes by 2 to get zero-crossings not peaks. Sorry for confusion, I do prefer scopes :)
And it should be sufficient for ESC based on zero-crossing. There are ways to do the same with interpolation and curve-fitting which requires less rotation...
And just to make sure, it is not 0.25rpm it is quarter rotation. You can convert it to RPM but to do that you need to know the minimum voltage range for ESC analog to digital convertor. BackEMF value based on RPM, but zero crossing is dependant of that.

Bottom line if we assume that 0.25V of backEMF is sufficient for ESC than quarter of rotation would be enough for ESC logic to get going. The RPM for given motor to get 0.25V of backEMF would be driven by motor Kv. You can put this all together.