Counter Strike

Make sure that you get servos that match the weight of your dispenser and the forces involved with it. Any proper model-building supply shop should be able to advise you. In you are going for a high accuracy - medium range dispenser helicopter tail-rotor servos are best. The bigger ones, they are 4cm by 2cm by 4cm. Why are they better- the helicopter servos move fast to just before the point it is supposed to be at and then slowly moves to the final point. Normal servos just move somewhere to the point where it is supposed to be at, often further than they are supposed to and then slowly move back to the final position. If you are on a budget the normal ones will work fine but you could do better.

Make sure the load is balanced over the servos, i.e. similar amount of weight on both sides (left/right) of the servo-axis. Additionally make sure that the weight is evenly distributed above and below the servo-axis, too much weight above the axis will put too much pressure on the servo to turn upside-down and too much weight under the servo-axis will make it want to level out. If you don’t do this not the servos will get overloaded/overheat and drain your batteries if you choose to use those instead of steady power supply. Also try not to use any connecting rods or leavers or anything that lowers the acuracy of the box, just connect everything directly to the servos. If they are not strong enough, get bigger ones.

We used servos that have 3.4kg/cm of torgue at 4.8 volt but obviously if you have a higher ambition you will need stronger ones. If you search a little you will find them at least 42kg/cm of torgue at 6 volt, like underneath. And fast too at 0.12 sec for a 60 degree turn.

For the tri gger of your dispenser you might consider using a servo-switch (or servo-relais/servo-relay) such as incorporated in this project in the Perspex box you can also see the lights come on when firing, cool factor feature. But more important it saves battery life, is faster and doesn’t move the dispenser after aiming it on the target. Additionally they cost as much as a servo can also drive other applications such as a solenoid, so why not. The model used in this project is the robbe single relay. It’s called a mono-switch (memory) no. 8444/8445. Remove the jumper from the board.

The servos are attached to the pololu module as follows:

Position 0 – horizontal movement

Position 1 – vertical movement

Position 2 – trigger