PDA

View Full Version : Discussion How could i add reverse to a forward only ESC?

doctor_prox
May 04, 2006, 03:38 PM
I know how to program pic chips to work with RC signals, i was wondering if i could use some electronics (i was thinking a big relay) that triggers on a certain channel and basically switches the motor wires to be in reverse.
This is for a car obviously.
Any ideas how it can be done because i dont think the relay idea will work (wont handle the amps).
Gary Warner
May 04, 2006, 04:12 PM
Use a double pole, double throw switch or relay. Same for BL motor except you are just working with 2 of the 3 wires.
meteor
May 04, 2006, 04:13 PM
I tried this a long time ago with relays...

But, with a PIC, you could look for a continuous application of full "brake" (say 3 seconds, or so), and then electrically disconnect the ESC from the motor, and apply a small reverse current.

You may be able to get away with an application of power directly to the motor terminals, as most ESC's are designed for regenerative braking, and could handle reverse current. (but the polarity might be backwards, not sure...)

A large resistor and a single FET may be able to apply the current you need for maneuvering reverse, and have enough impedance to avoid "normal" forward current from going back to the battery.

This solution removes the need for a seperate channel for the "switch".


Ideas?
doctor_prox
May 04, 2006, 04:50 PM
hmmm thats a much better idea.
The only problem i can see with that is the ESC may just let the current run straight back to the battery and not go to the motor as the ESC is designed to recharge the battery when braking.
meteor
May 04, 2006, 05:53 PM
hmmm thats a much better idea.
The only problem i can see with that is the ESC may just let the current run straight back to the battery and not go to the motor as the ESC is designed to recharge the battery when braking.


Although there would be a small resistance penalty, you could put three/four FETs on the motor-ESC lines and cut that part of the circuit while you apply reverse current. (some sort of R/C circuit on the gates would stop any momentary current cross-over)

Crude, but probably effective...