DIY Thrust Measurer
In order to test a motor / prop / ESC combo you can certainly read the specs on your equipment and hope the manufacturer did not inflate the data, or you can test them yourself on the bench before it is too late.
My dad is of the crafty types and to be able to experiment, test and verify propulsion systems for his fleet, he built himself a thrust measurer, which includes a scale and a watt/amp meter. It is a very simple device which can tell you basically eveything you want to know on a determinate combo before you burn something up.
The version shown here is what we could call V1, where there is a RX connected to an ESC to control the motor's RPM. It has been upgraded now with a servo tester, connected to the ESC, in order to avoid the TX/RX altogether.
He used a length of 40x20mm wood to build the structure, on which he attached all the equipment he needed.
Ideally you want a base which is large enough to guarantee stability, but which allows you to read the scale underneath it.
There are no fixed dimensions, but one important thing is to get the angles between the segments right. Starting from the base going up:
- 45° from the base (as long as you need)
- 90° corner. The second segment will bring the center of the propeller over the center of the base, so the lenght of this part is influenced by the length of the first.
- 135° third segment coming down vertically to mount the motor.
|The angles to use to build your thrust measurer|
|The scale and the watt/amp meter|
The idea is to have the propeller trying to push the whole device downwards, as vertically as possible, and as centered on the base as possible. This way you will have a pretty accurate reading of the thrust, the amps and the watts produced by any particular propulsion system.
Remember to always use a bigger ESC than what you need. I am pretty sure he strapped a 60A one here, even if he tests combos which rarely exceed 30A.
Remember also to use the battery you plan to use on your plane, because of how LiPos work, to get an accurate estimate of the performance you will get in the air, you need to use:
- THE MOTOR
- THE PROPELLER
- THE BATTERY
you will use on your plane.
Last thing to remember is that this is potentially dangerous. Propellers can spin VERY fast. So please DO NOT place your hands near it, wear safety glasses and be careful!
Until next time, happy landings!
|The motor holder, with 4 wing nuts to quickly attach and detach a motor|
|The square plates block the motor mount, and the wing nuts keep it snug|