Servo - September 2015

34 SERVO 09.2015

slightly lighter and more compact than the standard wiring, but much more work.

Servo and Battery Upgrade

Using the XQ Power 11V servo instead of the stock HXT servo gives me more torque on the arm, but less speed. More importantly, it allows me to run the whole robot using a 11.1V LiPo battery instead of 9V disposables (without the addition of a regulator).

This gives my drive a theoretical speed increase of about 22%. Also, the

11.1V LiPo battery holds more power and weighs less.

Servo Shock Mounting

The Viper lift kit instructions specify mounting the servo directly to the mounting bracket with #4-40s. I have been using servo lifter weapons in Ant and Beetleweight robots for many years, and my experience has been hard-mounting the servos increases the likelihood of the mounting ears (flanges) on the servo case breaking under the severe shock loads that are common in the combat arena.

I prefer to use the rubber grommets and brass eyelets included with most servos to help reduce the shock load on the mounting ears. The grommets fit into the mounting ears and protect them from vibration and shock. The eyelets press into the grommets and prevent over-tightening of the mounting screw.

The eyelets included with most servos are designed for 2. 5 mm screws which are slightly larger than

#4-40 screws which the Finger Tech servo mounts are designed for. In order to use them, I had to drill out the #4-40 threads on the servo mounting bracket, then use four M2.5 x 0.45 x 20 mm LG screws and matching nuts to secure the servo to the brackets. This also shifted the position of the servo slightly, causing the arm to not line up with the slot in the top plate. I had to cut away a little material in order for the arm to work properly.

Arm Pivot

Step 1 in the lift kit instructions states: "Attach the Mini Nutstrip pieces [to lifter arms] using two 6-32 x 1/2 screws with threadlock liquid applied to the threads. Leave just loose enough that they spin freely." This is a quick and dirty way to create a pivot axis. The threadlock liquid (similar to super glue) will keep the screw in place, but would make quick repairs in the pits difficult. This also means the polycarbonate arms are rotating on a threaded shaft which could dig into the plastic and cause the arm to not operate smoothly. Instead, I used a pair of partially threaded socket head cap screws. The non-threaded portion of the screws created a smooth bearing surface for the arms to rotate around, and Upgraded pivot axes.