When choosing motors and propellers for mini quad, we often just listen to rumours, or what&#;s suggested by the manufactures. To determine the optimal motor and propellers combination for your quadcopter and multirotors, the most scientific way is to test it yourself. I tried to look for a ready-made motor thrust measuring stand, most of them are either too heavy (made of metal), too expensive, or out of stock. Looks like it&#;s time for some DIY fun.

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Test video at the end of post. For more quadcopter tools check out our list.

Simple Motor Thrust Test Stand Design

The trickiest part of this project was the design. Even with mini quad motors, such as or sizes can easily generate over 1KG of thrust on 4S. If the thrust stand is not well designed the result error can be large, and it can be dangerous if the stand is not stable with the fast spinning propellers. I went through quite a few usual thrust station designs, most of them has this common configuration. They all have relatively strong base to ensure stability (one of the reasons why many commercially available thrust stand are made of metal).

Basically, there are two wood pieces, the right angle arms, and the base. The two parts are connected by a hinge so the arms are movable. The motor is mounted on one arm, and as the motor drives forward, the other arm pushes against the scale to indicate thrust generated by the motor and propeller. It&#;s simple enough to build, but requires tools and material that I don&#;t have on hand (drill, wood pieces etc). So I did my usual thing, sketched random stuff on paper and finally I settled on two even more simple designs.

The first design is quite similar to the above example, only it would be using only one straight wood piece, and it works like a balance or seesaw. The disadvantage compared to previous design is that the motor/prop is too close to the ground, which affects aerodynamic and the thrust generated.

Second design is my favourite, it involves no moving parts (no pivots), and I am able to utilize material that is available to me, some ZMR250 spare arms, and some spacers. The thrust will be pointing downward, so in theory this thrust stand should be relatively stable, I just need to make sure there is enough friction between the bottom board and the scale. Drawbacks are again, it&#;s too close to some surface and affects accuracy (thrust generated), also the props size that can be tested is limited by the size of the arms (how far the spacers are from centre). But I am mainly going to test 5 inch and 6 inch propellers only, so that&#;s not a problem.

Of course you also need a watt meter for recording current / voltage as well, and a servo tester to control the ESC/motor speed.

Building DIY Thrust Stand

So once the design is done, the rest is easy and straight forward. Here are the material and parts used.

Find the centre of the base plywood board, and find out where we need to drills holes.

I used a sharp knife and a pair of scissors for the job.

I glued the two arms together with Epoxy Glue. Once you fasten the motor on the arms, it also holds the two arms together firmly, so in theory you don&#;t even need to glue the arms together, but it&#;s more convenient to do so.

And I am happy with the result :D Added some foam at the bottom to make it a bit less slippery.

And finally tested it with a motor with watt meter, worked perfectly.

Here is a quick video showing the test:

Just another example :)

https://www.youtube.com/watch?v=LDu3Aww-koU

Accuracy?

Many are doubtful about how accurate this DIY gadget is. Some pointed out there is air flow issue as the propeller is so close to the bottom board. Indeed this is a issue that can affect final reading, and I did observe some inconsistency when measuring larger props on power setup.

I concluded that this thrust stand is good for measuring thrust range up to 500/600 grams. Anything larger than that, reading will be reduced than actual figure. I had pretty accurate reading with / motors with 5inch props, compared to manufacturer&#;s data.

In answer to Geoff's question, no, buy April's RCME instead, and save £57.

To challenge PatMc, how much testing have you actually done using static thrust?

Enough to realise that measuring it achieved no useful results.

Lets go back to basics. For the AVERAGE electric model we want three things:

If you are looking for more details, kindly visit propeller test stand.

1. There is enough power to get the plane off the ground and to fly well.

2. We need to know that the motor/prop/ESC combination is not going to draw more current than either the motor, ESC or battery can comfortably handle.

3. We would like the combination to be as efficient as possible, to get a longer flight time.

Actually that&#;s 4 things, none of which are predicted by measuring the static thrust of the power combo.

All we really need to be concerned about is static thrust and current draw. I use a very simple rule of thumb.

No disagreement regarding current draw.

If the static thrust is equal to the weight of the plane, then it is going to be a comfortable flying experience. The plane will take off easily from grass and have plenty of power for normal flight.

Neither is guaranteed by 1:1 static thrust/weight ratio.

If one wants unlimited vertical flight then the static thrust needs to be higher. High speed planes are a completely ballgame however.

Agreed vertical climb requires ST>W, the max speed of climb will be reached when ST-W = form drag.
I don&#;t understand why you consider high speed model flight is in a different &#;ball game&#; &#; AFAIK same physics apply throughout our practical speed range.

A static thrust test jig allows us to see the actual thrust of a motor combination, to note the maximum current draw, to compare different propellers, to set up the ESC and even to check different battery specifications, and all this can be done on the bench.

But you&#;re still only measuring a static force, not power. When used to fly a model thrust diminishes as soon as the model moves forward. It continues to diminish as the model accelerates, at the same time the model&#;s drag increases. When thrust & drag are equal he model will cease to accelerate. The interesting parameter to measure would be the dynamic thrust over the whole period of acceleration until equilibrium.
An ammeter will do the rest either on the bench or in a model.

You can check for such things as overheating and vibration. One can test different sizes and makes of propeller quickly and easily.

I fail to see where a thrust meter is any particular use here.

Once the model is built, everything can be installed, in the knowledge there is no further setup or fiddling required, other than perhaps setting up the ESC limits and failsafe when one first hooks up a receiver.

You may feel it necessary to try different props over the course of the first few flights whether you have run static thrust test or not. But if you haven&#;t done static thrust tests at least you won&#;t have wasted time in a pointless exercise before going to the flying field.

To come to Pat's point about it only being a static comparison, I've done tests in the air, using the full range of telemetry including airspeed, current draw, and motor RPM. As this is logged on the Taranis it is easy to look at the whole flight afterwards. I found very little difference between performance in the air and static testing.

You haven&#;t compared any parameters other than current & rpm neither of which are measures of the model&#;s performance.

If one is really pedantic, one might suggest we ought to test in a wind tunnel. That way we could check for propeller unloading. Actually a static test jig can do this too. Using either GPS or a pitot tube airspeed indicator, I know many of my models fly around the 50-75mph mark. Well, yesterday the wind speed was over 30mph as measured in the garden, so I did some testing, first with the test rig downwind, and then upwind, giving a windspeed difference of 60+ mph. Propeller unloading? Look into this and one will find much is concerned with ic engines, or real planes and then assumed to be the same with electric. In reality with the jig into the wind the thrust was 10% lower than downwind, not that big a difference really. The motor data suggested a thrust of 890g with a 4S, I actually achieved 670g using a 3S.

Wind tunnel testing of thrust wouldn&#;t help in actually predicting a suitable prop for a model.

A static test jig is a really useful bit of kit. At the end of the day, as telemetry (and the test jig) shows, with electric there is a constantly varying situation as the voltage drops on the battery, with a large drop within the first 30 seconds. To use the test jig, I log the current, voltage and thrust every 30 seconds on full power. From that data one can quickly compare different setups.

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