Operating Servos at Full Battery Voltage
If you are upgrading your Viper robot kit and have decided to add a servo; you will notice that when trying to run your servo it will twitch and not much else. What's happening is that the servo is trying to draw more current than can be supplied by the 5V regulator of the tinyESC. This results in a voltage drop that resets the receiver. What can you do to supply more current?
To get enough current to your servo, you can power it directly from the battery instead of through the receiver's 5V supply. This has added benefits too, since your battery voltage is higher than 5V (likely 7.4V or 9V).
Overvolting a servo (running it at a higher voltage than specified) gives an increase in speed and torque. HXT-12K servos are spec'd to run at 4.8V-6V, but can tolerate up to 11V. Careful though! Any higher will damage the servo electronics. Use a UBEC9V voltage regulator for batteries higher than 9V. See the diagram at the bottom of this page for wiring up a voltage regulator.
Since the Viper's HK-TR6A receiver is being supplied 5V by the tinyESCs, and the servo has to be plugged into the receiver, how can you overvolt the servo? It's going to take a bit of rewiring! Read on to find out how.
Servos have three wires:
- The first is a white/orange/yellow SIGNAL wire that tells the servo which position to turn to.
- The second is the red 5V POWER wire.
- Third is the black/brown GROUND wire that is the reference point for the others.
1. Separate the power wire from the servo connector of each servo you will be overvolting.
2. Tie all red servo wires to the battery's positive terminal. Shown here with a 7.4V (2-cell) lipoly.
3. Plug the servo connectors with the SIGNAL and GROUND wires into the radio receiver like normal.
4. The receiver will still need 5V-7.4V to operate. This will be supplied by the Battery Eliminator Circuit (BEC) in the tinyESC.
5. That's it! Your servos are now running off the full battery voltage with no current limitation beyond what the battery can supply.
Here is an actual setup using an 11.1V lipo battery with a UBEC9V voltage regulator:
(See the UBEC9V page for a detailed description.)