Servo Tester

thingiverse

I made this device to test and set up servos for my RC airplanes. My latest build was a sailplane with V-tail and spoiler, which required a complex servo setup. Each ruddervator servo received inputs from both the rudder control and elevator control, making it challenging to achieve precise results. The ruddeer stick demanded nearly twice the response on the rudder as the elevator stick, and I also wanted dual rates and expo. When the spoiler was activated, I needed to mix in some up elevator to compensate for the loss of lift. Before installing the servos into the sailplane, I wanted to ensure everything worked as envisioned. I tried connecting the servos and receiver on my desk but found it difficult to gauge exactly how much a servo responded to transmitter stick movement. This device allows me to measure the servo response in degrees with accuracy. There are two versions of this device: one uses rubber bands to hold the servo, while the other employs bolts. Both versions perform equally well, and I've designed them to accommodate various sizes of servos. The small KST 80 series servos shown can be replaced by larger ones without affecting performance. For the rubber band version, you'll need to print the rubber band base, dial (degree scale), and one knob. For the bolt-down version, you'll require the bolt base, dial, and three knobs. A piece of self-stick foam from an art supply store keeps the servo in place on both versions. You'll also need a 3M x 12mm screw and nut to secure the degree scale (dial) to the base. If using the base with bolts, two hold-down bolts (3M X 30mm) with four nuts are required. The nuts should fit snugly into the knobs. I've included a pdf for printing out the degree scale in various sizes. You can choose between a smaller or larger version by scaling the stl file. After printing the pdf, cut out the degree scale and discard the bottom half. Attach the scale to the tester using spray contact cement. To use this device, remove the degree scale, attach the servo with its output gear centered in the base cutout, then slide the degree scale onto the base so the bottom of the scale aligns with the middle of the servo output shaft and tighten it securely. Alignment doesn't have to be precise; I just position the servo by eye, which gives good results. Next, attach a servo arm, and you're ready to test your servo.