RC India

Returned after a long break. Decided to build a thrust meter for brushless motors.

Started by taking an aluminum shelf support. The angled section of the shelf support used for screwing it to a wall was cut off.  A hole was drilled in the aluminium section to allow for the motor shaft to pass through and additional holes were drilled for fixing the motor. Motors can be attached in tractor or pusher configurations.

The aluminum section was screwed to a wooden block 1" * 2" * 12" to form a L configuration. This was then attached to a wooden platform using a hinge so that the L section could rotate freely.

An electronic kitchen scale was placed on the platform. A support screw was attached to the wooden block. The distance of the screw from the hinge is equal to the distance of the motor shaft from the hinge. The screw is adjusted so that the wooden arm is horizontal when it is resting on the scale.
Plastic clips were attached for holding the wattmeter and ESC as shown below.

A holder for a servo tester was made and attached at the far end of the thrust meter stand. The servo tester is used for adjusting the speed of the motor. The finished thrust meter is shown below.

As the motor is revved up the scale will show the thrust reading while the watt meter will show the current/power being consumed. Planning to add a tachometer later.

While using the thrust meter I found that at high speed there is vibration at the contact point between the scale and the wooden arm. I plan to replace the screw with a rubber bung to reduce the vibrations.

A word of caution. Watch out for the propeller. I got a nasty nick on my right hand while doing my first test  8-). But the good thing is, it works !!!

Ingenious  :thumbsup:

Thanks Sanjay. Refinements in progress.  ???

To reduce the vibrations getting transmitted to the scale, I cut off the head of the screw which was used as the contact point between the lever arm and the scale. Threaded a piece of silicon fuel tubing and trimmed it to size. This I found helped in keeping the lever arm smoothly on the scale in my subsequent trials

Since the scale covered most of the base, I decided to attach the tachometer to the lever arm. I then bent an aluminum strip to accommodate my optical tachometer which is held in place with two rubber bands.

To keep away from the rotating prop (after the deep cut on my hand yesterday) I decided to change the inclination of the power meter for easier reading. I added a small piece of ply at 45 degrees for attaching the meter. To make construction easier, I first placed a triangular piece of balsa under the piece of ply.

Next was a trial run to see if all worked well together. I was able to measure the current, watts consumed, rpm and thrust at different throttle settings. However, the test run was with a large motor and the vibrations after 50% throttle were at an undesirable level. So back to the drawing board. The aluminum bar though quite sturdy, still vibrates at higher speeds. Plan to revert to my original design of using two wooden blocks for the lever arms. Will make these modifications and see how it all goes.

The build however looks promising for deciding on the most efficient prop./motor for an application.  ;D

Mr Baijal told me that the whole set up tried to run away when powered over 50%.

A question for newbies.
If Mr Baijal puts wheels under his rig, what would be the effect on his thrust readings?

Iyer sir, like this?

(http://s25.postimg.org/4zp0f3b5r/20140825_165931.jpg)

(http://s25.postimg.org/4zp0f3b5r/20140825_165931.jpg)


Full details here : http://www.rcindia.org/electric-power/selection-of-motor-esc-prop-and-lipo-for-foam-planes/25/ (http://www.rcindia.org/electric-power/selection-of-motor-esc-prop-and-lipo-for-foam-planes/25/)

@Sanjay,  The Coromaster
Now this is what I call ingenious.

Great one Ashok Sir and Sanjay Sir....

Added a wooden block to the aluminum lever arm. I did not remove the aluminum bar, but screwed on the wooden block to it. This will prevent the vibrations that I experienced at high speds.

Prepared "U" shaped blocks for motor mount. Since different motors have different mount hole spacing, I have prepared more than one motor mounts. The motor mounts are held in place with two wing nuts to allow ease in change of mounts. The wing nuts were placed in the centre of the vertical lever arm so that the motor mounts can be attached in both tractor and pusher configurations using the same motor mount.

The test run was quite successful with no unwanted vibrations even at full speed. The thrust readings were available in both tractor and pusher configurations.

Next would be a coat of paint and finish before test runs of my motors. A successful project  ;D

Sir, I am not able to understand how it works. Is it in tractor or puller configuration. I am interested in building a thrust meter in my Christmas holidays so that I am not bored. I don't have a puller prop so I would like to make one which had pusher or tractor configuration.

Picture 3 in reply #16 is Tractor mode setup while 4th picture is pusher configuration. The thrust meter works in both modes.

@rcrcnitesh,
You may have seen this, referred to by Mr Baijal in another recent thread
http://www.rcindia.org/electric-power/selection-of-motor-esc-prop-and-lipo-for-foam-planes/?action=dlattach;attach=698332;image

The pictures below should explain the working of the Thrust Meter mechanism.

Thank you Sir for posting these diagrams.
My question is what is the use of hinge in your setup?
What I think will happen with the pivot you've attached is in the diagram given by me. It won't be showing any amount of thrust while taking the reading. Please correct me if I am wrong.(https://f4k3url/photos/2PeiSuPDXwrcoB4d9)
Please bear with me for my silly questions.
(https://uploads.tapatalk-cdn.com/20151223/00964a2580f98655160ed1c56c97a92d.jpg)

@KK Iyer Yes sir I have seen that but that is in pusher configuration if I am not wrong.

The pivot is around which the L shaped lever turns. If you understand how levers work, the pivot point in the diagram is the Fulcrum, which is a zero friction point around which the lever is supported and turns. The moment is calculated based on the distance of force from the fulcrum. In practical terms, the hinge is used as the pivot/fulcrum. The Work and Effort will be the same as the distance of either from the fulcrum is the same.
I hope the terms used are correct. I studied levers in1964.

No, it can be used either way.
I run it as a pusher to avoid the risk of liftoff at full power!
But actually none of my motors can lift a 2.5kg brick  ;D

Sir thank you so much now I understood how it works! (https://f4k3url/photos/1Xb34U5VyWVN6Xw96)
(https://f4k3url/photos/eKgcB2mviiwGVW4x9)
(https://uploads.tapatalk-cdn.com/20151223/1349019814cac5f8629d17bcb2a4b285.jpg)(https://uploads.tapatalk-cdn.com/20151223/1f189a937d1cfd2da000b0a1b5a6987c.jpg)

@KK Iyer sir how would it be able to measure thrust when the block is rising?

Iyer Sir, what I am trying to say is while measuring the thrust in tractor configuration how will we get the readings when the  lock is being pushed away and not pulled.

Please bear with me, I am not so good in physics and are my above drawings right?

Try this simple setup. Ensure that the thrust is downwards by ensuring that the front portion of the prop is pointing downwards and setting the direction of rotation of the motor so that thrust is downwards.
Exercise caution while taking readings as the blade is horizontal and not visible when turning. Also ensure that the block does not topple due to vibrations and cause damage/injury.

Nitesh,
I've seen 3 models in the forum.
1. Tractor. Sanjay sir's tension model. A trolley with wheels. Thrust measured by a spring balance type scale in tension.
2. Tractor. Baijal sir's fulcrum model. Motor pulls vertical arm, horizonal arm presses on flat type electronic scale.
3. Pusher/tractor. My Brick model. Used normally in pusher mode, so that the thrust presses the scale down. When you keep the device on the scale, it reads about 2.7kg. Pressing the Tare button zeros it. When motor runs in pusher mode, scale shows a positive value. When in tractor mode, it shows a negative value.

In tractor mode there is the danger of liftoff!

Model 1 can be used in pusher mode by attaching the spring balance to the other end  ;D
Model 2 can be used in pusher mode by keeping a weight (more than expected thrust) on the scale and zeroing it.

After these long lessons  ;D here's an experiment for you:
1. Is there a difference in thrust between the two modes? Why? Is there much difference?
2. Does fitting the prop one way or the other make a difference?
3. How does a pusher prop compare with a normal one of same size, shape and brand?

It would be nice if you try the above and report results on the forum.
Regards (BTW, hope you saw my PM on a different topic!)

A small clarification.  My setup works on both modes. The motor mount is reversible as described and pictured in earlier posts. ;D

Here's my bit to it ..... A design in which the applied thrust is not in line with the measuring device a moment arm is created and hence the reading would be less than the actual thrust .

Here's my design where in I have tried to keep the measuring device in the line of thrust .
(http://images.tapatalk-cdn.com/15/12/24/4f5d529780242055f0441081ca1b4f1c.jpg)
(P.S.   Even in this design, the measured thrust would be slightly less than actual, as that part needed to over come the friction in the channels goes unmeasured, but that can be calculated and kept as a standard addition )

 :rofl: :rofl: reminds me of our earlier discussion ;)

Yes Sanjay Sir . ... No doubt you have a sharp memory :)

rcnitesh you need to place the motor on the other side for pusher

Thrust meter built with sketchup

https://drive.google.com/file/d/0B1PSuFLMpZcFZG1IX0MyWHNkV2c/view?usp=sharing (https://drive.google.com/file/d/0B1PSuFLMpZcFZG1IX0MyWHNkV2c/view?usp=sharing)

sketchup version.
https://drive.google.com/file/d/0B1PSuFLMpZcFMUFzaFEzZDJxRzQ/view?usp=sharing (https://drive.google.com/file/d/0B1PSuFLMpZcFMUFzaFEzZDJxRzQ/view?usp=sharing)

Forgive me for any mistakes and point it out.

With regards,
Nitesh

Nitesh,
Come on, surely you can do better than this!
Regards

Sir can I know how? Is there any mistake in this design? I am going to start the build tomorrow because till today I was scavenging around for the materials :p.

With regards,
Nitesh

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Have a look a ... A simple thrust measuring setup.. myrahulroy.blogspot.in/2016/01/motor-testing-rig.html?m=1

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