Weapon Control

Flywheel Switching

Ruf Ruf Dougal’s flywheel takes 30 amps at 24v to rotate freely. Originally this was switched using a 12v, 70 amp Tyco relay which worked fine until ‘Shunt’ stalled the flywheel with his scoop after which we suddenly found we couldn’t switch the weapon off………. Not a nice situation. On further inspection the stall current was found to be 230 amps, far more than the relay or the motors could take for a prolonged period. The countermeasures for this dangerous situation were two:-

Firstly the relays were doubled up ie. Two 70 amp relays in parallel, giving the capability for 140 amps continuous.

Secondly the switching was changed from a toggle switch to a ‘hold for on’ push button.

Two relays in parallel is not a normal thing to do because they may not switch together. This would allow one to take a large surge current on starting but in this case each relay is easily capable of starting the motors by itself, the need for the second is only to absorb excess current during stall.
It must be clear that two 12v car ABS motors won’t last very long when stalled and on a 24v supply. I had hoped that the pulley would slip on the flywheel but it wasn’t to be. The push button switch was the easiest and most foolproof way of disconnecting the supply in an emergency. ( I trust my brother implicitly)…. Fuses on a total destruction fighting machine don’t look good on the FMEA (Failure Mode Effect Analysis).

Relay Switching

The Tyco relays are switched using a single home made 'Ken Hewitt' switch, diagrams of which can be found on his website. See the 'Links & Thanks' and 'Constructor Tips' pages on this site. The relay coils are wired in series and take about 12v each. This obviously depends on coil resistance but they will still switch at 9v so I'm not too worried.

Failsafes

My Radio gear had inbuilt failsafes so the weapon should fail safe under all condition (except welded up relays)!. See the 'Radio Control' page on this site.

Weapon Control Switch	R/C switch