Just as the topic title says, is it dangerous to run dual FOCBoxes connected via CAN at different gear ratios? One is at 1:4 and the other is at 1:2.5.
I only ask because I’m trying to test my gear setup that I just made for one side of my dual setup until I get more filament tomorrow, and I don’t want to have to disconnect the other motor or speed controller if I don’t have to.
it should be fine, I would suggest yo do motor detections individually and then connect via CAN or Split PPM. If you can run different KV motors with no issue I don’t see any reason why different gear rations would matter.
you don’t want to push either motor above its no load speed with the other motor. this will create drag and potentially overheat the over-no-load-speed esc w/ reverse-current (the back emf voltage generated by the motor will be higher than the pack voltage.) it could even harm a drv chip if the back emf voltage from the over-no-load-speed motor reaches above ~60v.
This is what I was worried about. Say my max speed on the slower tire, as an example, is 25 as opposed to 35mph on the faster tire, if I just limit my speed to 25mph I should be okay then, right?
yes limit top speed to the no load speed of the slower motor. above that speed the slower motor will be generating more bemf voltage than the pack voltage which can harm an esc.
I’m making some assumptions on gear ratio, but I think you guys might be making problems where they don’t exist. The ERPM limit will stop the top speed from making too much of a difference.
I may be wrong, but if so I dont see it.
This spreadsheet is dope, should upload to Google docs and share with us all. Contains far more information than calc.esk8.today contains
the issue is when the 2.5:1 motor is above its no load rpm, the back emf exceeds the pack voltage and the reverse current path is through the diode in the mosfets. the electrical resistance of the diode reverse current path is significantly higher than the mosfet ON resistance, so any reverse current through that diode will produce much more heat in the mosfets than normal forward current through the normal mosfet ON pathway. also if the bemf voltage from the 2.5:1 motor exceeds ~60v it could blow the DRV chip. these issues have nothing to do with the erpm issue.
It’s shared in a thread somewhere, I don’t remember where but I’ll re-share it when I get to work tomorrow.
What the heck? Just running the motor for a while or actually riding it? If riding, I would think that if one motor is turning faster than the other wouldn’t it be trying to turn the board? Make sure traction control is off.
Here ya go…
I’ve been running different gear ratios since before I can remember (via split PPM). Never had an issue
Awesome thanks mate