Controlling 3 things with 2 channels

I have a 2 channel transmitter/reciever. I have changed my design and want to include a weapon, but I don't want to buy a 3 channel reciever.

I want to have it so that when the left stick on the transmitter is down and the right stick is neutral, the weapon motor turns but the drive motors do nothing. I also want the weapon motor to turn the other way when the right stick is down and the left is neutral. I'm sure this is possible using relays but I can't work it out! Has anybody done anything similar?

P.S. I am using a speed controller.

Hi,

I understand that you don't want to to pay for a new TX and RX when you have a 2 channel set. But here is the thing: it is already hard enough during battle to concentrate on the fight, steering, and use your weapon. The last thing you want to do is complicate things even further than they are. You want to be able to focus on the fight, not fuss making some electronic circuit measuring the 2 channel signals to do what you want to do.

I asked for advice on this forum a while back and everyone told me to buy a spektrum. I was really reluctant to spend the money when I already had radio gear, but now I have done I think it's one of the best decisions I've been told to make. So I'd say the same really. If you want your robots to get more complicated, make life easier and invest in some proper radio kit. It'll should last you for life (or at least until the next must have piece of kit, lol)

Leo is correct. Unless you want your weapon to operate continuously (slaved to one of your motors, for example) you need to provide a third channel. Try driving your robot in an arena, with 15 other competing machines, in front of large crowd, and I'm sure you will agree that any weapon control needs to be simple and intuitive. For this reason some teams have two operators - one to drive the robot the other to trigger the weapon.