Help me build motor thrust tester

Motopreserve

Motopreserve

Drone Enthusiast
Hey folks,

I've had this bench top motor/prop thrust tester project on the back burner for a while, and I want to see if I can button it up tonight. Just want to run the process by you to see if there are any tweaks or fixes before I fire it up. I've been a little frustrated by the lack of info out there on the motors I've purchased, and at worst there has been some manufacturer misinformation about basic values (wrong pole count etc).

I have put the tester together in a basic way with cheap/found parts. I'd like to make sure it's safe and effective, and then maybe I'll make it better/pretty :)

currently I followed designs that create an equilateral triangle (it has some extra space off the end - so maybe it's an Isosceles triangle) out of 2x2" wood, with a separate wood base (1"x3") with "feet" that attaches with a door hinge. The one end rests on a scale (reading in grams), which is level with the base. This leaves the bottom of the triangle perfectly level on a digital leveler.

I have a cheap HK-010 power analyzer hooked up between the battery and an electrical block (for easy connections of various components). The block then has outputs to the ESC/motor. The motors will be mounted using a mount that I had lying around from an old build, which is attached securely to the vertical arm. The ESC is driven by a cheap servo tester - which I used to calibrate the ESC throttle settings. I've also flashed the ESC with the latest simonk firmware (June 18, 2014?).

My goal is to get readings for amps and watts being pulled, as well as monitoring voltage for various motor and prop combinations.

QUESTIONS:

1. Is there anything I'm missing? Improvements?

2. Would it be more wise to set up an RX to run the ESC/motor from a radio instead of the servo tester? I have marks for 50% throw! but that hasn't been tested scientifically. Is there a way I should test this with a multimeter?

3. I have the motor mounted facing away from the scale end. So I turned around the prop around (upside down from normal installation on an MR) so that it's facing the scale end. Does this make sense?

Any tips are much appreciated.

Scott


thrusttester1_zps86a35f2f.jpg


thrusttester2_zps4cf4984b.jpg


thrusttester3_zps53930362.jpg
 
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Q

Quinton

Active Member
I did (bought) the same sort of thing last year to do my own tests.
I got the Tahmazo Thrust Meter http://www.singahobby.com/?q=node/13499 and 130A watt meter/Power Analyzer http://www.amazon.com/Power-130a-Precision-Meter-Analyzer/dp/B0090YW78U
Also used the same simple servo tester as you have, although it was not very accurate at all, so I changed to using a transmitter so I could see where 25/50/75% etc really was, the servo tester did not seem accurate at all.

In your picture I can not really see where it is pivoted to get your thrust (usually 55-65cm from centre depending on what you are flying.) if using 1m length.
FerdinandK might be your man for this kind of thing, me I was just messing around with different prop setups to see what would be the best with my motors, it was REALLY interesting, and you are right I found completely different findings to what was online.
Just make sure you put all your papers away, as they will be all over the place when you finish :)
 

Motopreserve

Motopreserve

Drone Enthusiast
Thanks Quinton. The pivot is right at the bottom of the vertical arm. The book keeping the weight on the base is in the way of the shot.

Im finding the servo tester the wink link. I'm going to set up the RX for a more accurate reading.

EDIT: I see yours has the motor facing proper - so the backwards prop doesn't apply to your setup.
 




Motopreserve

Motopreserve

Drone Enthusiast
It's funny you say that. I just tested 3 props. (Xoar, hqprop wood, APC). The xoar got the best marks for the tests I just did. The APC actually got a bit more thrust going, but also drew more juice, so these xoar will likely be more efficient when I can get better data.

I know I'm not totally there yet with this thrust tester - but I figured trying it out would give me some ideas. DEFINITELY need to secure the hinge better. Also need to rethink the motor mount. It's glass fiber now - but I had milled a nice piece of aluminum for the mount earlier and scrapped it for expediency. I think I'll be going back to that on the final design.

The Rx will take the place of the servo tester and I think I will install a peg on the end of the arm that contacts the scale.

I also have a cheap RPM reader that I use to tune the old metal working machines. It worked pretty well - although the tape that it reads probably throws off the balance a bit.

I'll check out your findings now...
 
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Old Man

Old Man

Active Member
A simple hobby grade tachometer works quite well for obtaining RPM data without the need for reflective tape on a propeller. Back up the info from your Watts Up with a decent VOM. Calibrate your scale at several points, low, medium, and high. Most scales have some level of hysteresis somewhere in their weight range and it's good to find out where that is to avoid generating skewed data. If you can, perform your tests with both a TX/RX and a servo tester. You might find the throttle response range is considerably different between the two. I did using Futaba and tiger products. More throttle travel with the servo driver than with the transmitter, even after calibrating the ESC to the radio.

FYI, a thrust stand does not have to be at right angles. They can be a flat bar with a center bearing point but you have to assure both ends are equal weight and length from the bearing/pivot point.
 

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Motopreserve

Motopreserve

Drone Enthusiast
Thanks Old Man. I've seen plenty of nifty stands - this just seemed the simplest. Not sure if I would change it when I rebuild it. It was interesting to see the data differences between props. Even if the stand is not reading perfectly scientific, it should be reading similar for all props unto itself.

I was rushing to get this done tonight so I can slap the motor back on the hex, but in the future I will be taking more time with the build and the testing. There's a FrSky sensor I could use for RPM, but this worked fine for now. Not too big of a deal to remove the tape from a couple motors. If I end up using this more I may try to rig up that sensor.
 

Old Man

Old Man

Active Member
Understand. My stuff was for establishing absolutes to develop data for creation of large heavy lifters, for more generalized, or comparative, information ultra precision just isn't practical or necessary. What works best is all you need. Good set up you have going there.
 

Motopreserve

Motopreserve

Drone Enthusiast
Old Man said:
Understand. My stuff was for establishing absolutes to develop data for creation of large heavy lifters, for more generalized, or comparative, information ultra precision just isn't practical or necessary. What works best is all you need. Good set up you have going there.
Click to expand...

Yep. Not trying to get too crazy just yet. If I can get decent data, that will be great. But for now I have a good idea of what props may be more efficient with this motor etc, without breaking the bank. But if the next stand turns out to be a neater, tighter build, I'll invest in a decent analyzer and see how accurate I can get.

Thanks for the help folks.
 

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