Build a Simple RC Motor/Propeller Thrust Gauge

I have been building and flying radio controlled airplanes for about two years now and every once in a while I like to experiment a bit. I had the idea of using two propellers on the same motor to see what power increase I might get and what the handling characteristics would be of the aircraft.
To test the thrust or power of the motor and propellers I built a simple thrust gauge as outlined in the following steps.

The video shows the use of the gauge in testing the dual propellers.

There are many good thrust gauge designs and documentation on the web. There are also some commercial ones you can buy but this one is so easy to make that it seems more worthwhile to build your own.

Here are a few links to some websites that describe thrust gauge projects:

http://www.rcgroups.com/forums/showthread.php?t=511564

http://www.rc-cam.com/forum/index.php?/topic/2365-my-little-automated-thrust-test-rig-project/

Make the Thrust Gauge Arms

To begin this project you need a 90 degree wood arm. I had a collapsible coat hanger made of hardwood that I wasn't using so that became my principle source of parts.

I had a t-bracket and just drilled some matching holes and bolted two hardwood arms to the bracket.
Note: leave the middle t bracket hole empty, as this will be the pivot point of the arms.

The second photo shows another strip of wood bolted to one of the arms. This will be the upper arm that the motor will be attached to.

The third photo also shows a short piece of wood bolted to the lower arm. This piece will rest on the scale used to measure the thrust. The length will depend on how tall your scale is and what you are putting your thrust gauge platform on.

Make the Thrust Gauge Platform

The platform is what holds the thrust gauge arms up and in contact with the scale.
The first photo shows a couple of 90 degree brackets mounted on an ugly piece of wood that I use for drilling stuff. I like to reuse everything. The brackets are offset so that a bolt can go through two matching holes. Most brackets have the holes centered so there will be no need to offset them. The bolt will hold the thrust gauge arms as shown in the next photo.

The last photo shows the platform sitting on top of a toolbox with the lower arm resting on a kilogram scale.

Mount Motor to the Upper Gauge Arm

Now we mount the motor to the arm. Very important point: the motor must be mounted the same distance from the arm pivot point as the little arm on the lower gauge arm is from the pivot point - otherwise your thrust readings will be off.

I used zip ties to mount the motor over a small piece of epp foam.

The second photo shows the motor attached to the electronic speed controller (ESC) which is attached to the radio receiver.

The final photo shows the whole rig ready to go.
Zero the gauge.Turn motor on, turn radio transmitter on and engage throttle. Approximate grams of thrust can be read on the scale.

Important warnings:
- be sure the lipo battery and esc wires are behind the propellers
- be sure to keep hands away from spinning propeller
- be sure you have enough weight to hold the gauge down as the propellers thrust can turn the gauge over
- be sure the motor is spinning in the correct direction and that the propeller is facing forward