Help with BASIC Stamp II and Servos

DC Hurricane

I'm trying to simply power a couple servos with a 4 AA battery pack. When I plug the servo directly in to the battery pack it will only spin one direction. When I connect the battery pack to the BASIC Stamp II carrier board directly and wire it through Vin and Vss I can get it to change directions and work properly but I didn't want to do this because I read you could hurt the motors. Does anybody know why this is not working properly? Also one of the servos I have won't move at all anymore no matter how I connect it. I think it has something to do with using the servo controller board with it but I'm not sure. Any suggestions?

Thanks

Mike Green

Servos work fine powered directly from a 4 x AA battery pack. There's no particular advantage or disadvantage to connecting the servo to the Vin/Vss connections on a carrier board. Mostly you get the use of whatever power switch that's on the carrier board. There's probably nothing else between the power connector on the carrier board and the Vin/Vss connections.

If it works using the carrier board, but not using a direct power connection, then there must be something else you're doing wrong and I can't tell from your limited description. I suggest you make a schematic diagram of your two setups and post that as an attachment to your next message. Make sure the diagrams reflect your actual connections, not what you think you have ... often the two are different.

DC Hurricane

I program the board to go from center to counterclockwise to clockwise and have the battery pack connected directly to the board with the signal going to pin0 and Vin and Vss connected by wire to the power and ground on the servo. It works fine. I then take the 6v batter pack and connect a clip to it and stick the wires of power and ground directly to the servos power and ground, keeping the signal from pin0 the same and it only spins in one direction. In the second configuration I also have to power the carrier board with a 9v since the BASIC Stamp II needs a power supply of its own.

Mike Green

You have to have a common ground, so you have to connect the (-) side of the servo power supply to the Stamp's Vss.

DC Hurricane

Ok thank you. Am I able to solder the through-holes on the board together in order to carry on the voltage to supply my other servo and sonar sensor? Also will the current drop-off be too much to not be able to power the other components?

Mike Green

1) When I've used the Stamp 2 Carrier Board, I've used a piece of stripped solid hookup wire as a sort of buss-bar, run it between a group of through holes, then laid a bead of solder bridging the through holes with the wire between them.

2) The servos are the largest power drain. Under heavy load, they can draw as much as 1A each. Average current when running lightly loaded is on the order of 1/4A and the idle current is even lower.

3) Regarding wiring ... use common sense. Look at the cable coming from the servo. It's probably 6-8" long. You could easily double or triple that length using the same size wire and do just fine. Longer extensions and you'd want to use heavier gauge for the power leads and you'd want to do something to reduce noise on the control signal lead.

DC Hurricane

I was trying to hook up the servo to do gears and took the screw out to put a lego gear on the white part and screwed it back. It seemed to rotate it first at the same speed now it seems like the servo has lost a significant amount of power. I reassembled the servo again and tried resetting the set point again but it only goes about half the speed it used to. Do servos lose power that quickly or could I have messed up something internally in the servo?

DC Hurricane

They said I need to power it separately. Earlier you told me with this problem that I had to connect everything to a common ground. Does this mean a wire from the servo has to go to the board's ground as well as the ground terminal of the battery clip?

Mike Green

The ground wire (usually black) from the servo has to connect to the servo power source and the Vss (ground) terminal of the Stamp or Stamp board. The reason is that any circuit has two wires (+) and (-). In the case of the servo, you have a power circuit with (+) usually the red wire and (-) usually the black wire. You also have a control circuit with (+) usually the white wire and (-) also the black wire. The control circuit goes to the Stamp and the power circuit goes to the battery or AC adapter providing power for the servo motor and electronics.