[Jay Lundy]

I wouldn't recommend it. From what I gather, the speed controllers output 12V pulses, not variable voltage from 0-12. This is due to the pwm nature of the signal. I don't have an oscilliscope to test this with, but using my multimeter on both AC and DC voltage it seems like this is correct.

And even at full power I don't think its a steady pulse of 12V, but it might be. Once again I don't have an oscilliscope to test it with.

By the way I don't know the ruling on this, so it could be illegal too.

Did you run out of spikes or relay ports? If you ran out of spikes you can order more. If you ran out of relay outputs you can just use digital I/O pins for the FWD / REV pins on each additional spike.

[Edit]Also, did you know that you can wire 2 solenoids to each relay? That means 1 double solenoid or 2 single solenoids per relay. Basically the M+ and M- pins on the relays are independent of each other. FWD controls M+ and REV controls M-.

If FWD is high (5V), M+ is high (12V).
If FWD is low (0V), M+ is low (0V).
If REV is high (5V), M- is high (12V).
If REV is low (0V), M- is low (0V).

Just wire all the solenoid grounds to the main battery ground, and all the power wires to a different M+ or M- pin. It helps not to think of them as just FWD and REV but as independent pins, just together on one relay.