Lynxmotion Robotic Arm Servo Problems

So, I recently borrowed a lynxmotion 5robotic arm from a local school to help teach a robotics class. The arm has 6 servos with 5 degrees of freedom. I hooked up all the servo's power to the “5v” power output and then I used the digital outputs to send the pulse width signal.

The problem I'm having is that when I connect all 6 servos they all have very little power. When I run them one at a time they are very powerful, but I'm assuming that the Arduino can't carry the load of 6 servos. I bought a variable wall power converter from radioshack and I hooked up all the servo power lines to the 6volt output of the converter and I left the signal wires hooked up to the digital outputs on the Arduino, but now the servo won't respond to the signal. It clearly has power, but doesn't move the same way it does when I hook it back up to the Arduino 5volt power.

Is there anyway that I can run the servos on an external 6 or 7.2 volt power supply? Or is it possible to somehow draw more current from the Arduino to control all 6 servo motors and have a powerful arm?

Any help would be appreciated!

This is a picture of the arm from the website. They seem to offer their own micro controller, but the kids we're teaching are already learning on the Arduino so I don't want to change that.

I'm surprised the Arduino drives one servo well; the circuit isn't designed for that sort of load.

I bought a variable wall power converter from radioshack and I hooked up all the servo power lines to the 6volt output of the converter and I left the signal wires hooked up to the digital outputs on the Arduino, but now the servo won't respond to the signal. It clearly has power, but doesn't move the same way

Does it move at all? Do you have a common ground connected between the power supply and the arduino?

-j

I bought a variable wall power converter from radioshack and I hooked up all the servo power lines to the 6volt output of the converter and I left the signal wires hooked up to the digital outputs on the Arduino, but now the servo won’t respond to the signal. It clearly has power, but doesn’t move the same way it does when I hook it back up to the Arduino 5volt power.

Have you connected the ground from the power supply to the arduino ground?

Wow, that works! Thanks for the advice.

For the record, why is it that I must connect the power supply ground to the Arduino ground. I just want to know so I can explain it to someone if they ask.

Lastly, I noticed that when i use 6volts or 7.4volts the servos jitter and vibrate. They do this even when there is no signal line connected. Lynxmotion says that the servos are designed to run at 6volts and that only higher voltages will cause a jitter.

Good to hear that its working.

The grounds have to be connected because that provides a common reference between the Arduino and the servos for the voltage level on the signalling pin. Without the grounds connected, the servo can't determine when the Arduino is setting a pin high or low to control the servo position.

If the voltage in your supply is a little too high, you can drop it by connecting diodes in series. Each diode will drop around 0.6 volts, you can use as many as you need to get the voltage below 6 volts. Any standard regulator diode that can handle the current would work, for example something like a 1N4001 which you can probably get from Radio Shack.

If it still buzzes with that power supply even with the voltage under 6 volts than it may be that the output is not clean DC. If that's the case, you could try connecting an electrolytic capacitor to see if smoothing the output helps (make sure it's a DC supply and the cap is connected the right way around)

I hope that helps.

why is it that I must connect the power supply ground to the Arduino ground.

Either the Arduino or the power supply had a ground wire missing. The ground wire is necessary to complete the circuit so that electrons have a path to flow.

Another way to look at it is to remember that a voltage is a potential [u]difference[/u], and if you don't have a second connection there's nothing to measure the difference between. E.g, that 6V wire on the power supply is 6V potential above what? The power supply ground.

-j