I bought a DYS D3536 motor on Robu and a orange 9x4.5 inch propeller and wanted to test it's thrust. So I rigged a thrust stand to check it.

But it seems to only producing 700 grams of thrust while drawing 400+ Watts, that doesn't seem right. What else can I do to properly check it?

@GlamHawk,

DYS 3536 motors of different kv's are rated at 470w to 750w.

Please tell us the kv and the number of cells in the lipo.
If you have a tach, tell us the rpm at full throttle on the 9x4.5.

Regards
Iyer

@GlamHawk,

I note that you haven't been online since posting your query.
Please see my previous post.

There are two possibilities:
1. Bad motor
2. Measurement error

The simplest way to check thrust is to mount the motor on a wood block, stick it with hot glue to the plate of a kitchen scale. Then put the prop on backwards and run the motor in reverse.

Hope this helps.
Regards
Iyer

Quote from: GlamHawk on November 30, 2023, 12:22:11 PM
I rigged a thrust stand to check it.
But it seems to only producing 700 grams of thrust while drawing 400+ Watts, that doesn't seem right.
What else can I do to properly check it?

It's a 1450 Kv motor and it's a 3s 2200 mAh 30 C battery. It drew more than 400 Watts at full throttle while producing only 700g of thrust.

I did initially check it by directly placing it on a kitchen scale and ran it reverse. It pretty much the same (400+ W and only 700 grams).

Also I have an another motor D2836 1120 Kv motor which drew around 210 Watts which produced 500g of thrust with the same setup.

@GlamHawk,

Here's what I think is happening.

At no load, a 1450kv motor should turn 17400rpm on 12v.
Or 290 revs per second.
On a 4.5" pitch prop, this means a pitch speed of 1305" per sec, or ~33m/s.
Thrust of 7N at this pitch speed needs 231watts.

But this is in theory.
If you assume 75% motor efficiency, and 75% prop efficiency, the power required is 231/0.75/0.75
Or 410 watts!

So what that tells me is that your setup is running at 56% efficiency. By the way, 75% is a fair estimate of the efficiency of the motor, as well as prop.

To be contd...

That is a pretty good explanation of what could be happening.

I chose this motor mainly because I've seen Thrust tests of this/similar motors producing anywhere from 1-1.5 kgs of thrust while drawing the same power as I do (~400+W). That is my required range.

So, how can I get that level of thrust? Swapping the propeller out for a efficient one? Any other motors that are available in India, that will produce 1 kg+ thurst on a 3s battery. (Preferably with a 9-10 inch prop).

Here are some examples of specific static thrust vs input power:

1. Your 3536-5, 1450kv. 700gms, 400w. 1.75gms/w
2. DYS claim for same motor. 1450gms, 655w. 2.2gms/w (This is very low performance)
3. Your DYS 2836, 1120kv. 500gms, 210w. 2.4gms/w
4. My D2830, 1000kv. 525gms, 89w on 3s and 9x4.7 prop. 5.9gms/w
5. Same motor on 4s and 8x4 prop. 720gms, 140w. 5.1gms/w.
(For 4&5, see recent "Manu's Spad" thread)
6. My D2836, 700gms at 11.4v, 12.6a, 140w on 9x6 APC prop. 5gms/w (from my old notes)

Obviously something is not okay.
Either something in your power train is consuming excess power, or the thrust data is understated.

Please try a 10x6 prop on 2s.

Static thrust isn't everything.
But 2gms per watt is unacceptably low.
For this range of performance, one would expect 4-5g/w or better...

Thank you for your responses till now. I've already ordered a better ESC, maybe will try once again using different propeller.

Currently using a orange brand propeller from robu. Is there any other websites that has better/different brand propellers?


Also is placing the motor directly on the weighing scale a good way to measure thrust? I've read somewhere that it cause airflow issues due to close proximity to ground especially for larger propellers.

My thrust reading from the thrust stand as well directly mounting directly on the weighing scale matches.

1. Changing the Esc is s good idea.

2. Can you lipo do 40+amps without the voltage sagging to 11v or less? Use larger capacity

3. Thrust meter. Mounting the motor directly on the scale is enough to give an approximate idea. Earlier I used to screw the motor to a 6"x1.5"x 1" wood strip, strap that to a brick, and put the whole thing on the scale. That provided some more airspace below the prop. Now I have a better one! See pic.

4. Props. Left to right in pic, in increasing order of performance. Don't have comparative data, based on experience of use

Orange. Cheapest. Low performance
GWS. Called HD or DD, I think. Ok for small motors only due to hub/hole size.
Haoye HY Slow Fly. Good for low kv. Not for high rpm
APC clone. Good performance, strong. Original APC would probably be better
EMP. Excellent. Expensive.

I haven't checked what props are currently available. Will look. You also check LHSs.


P.S.
Some more data from my old notes:

- 2830/11 1000kv, 900+gms, 184 watts, 10x4.5 (probably SF). ~5gms/w
- DT750, 750kv, EMP 10x5 prop, 11.4v, 10a, 114w, 650gms thrust. 5.7g/w
- Same motor, EMP 11x5.5 prop, 168w, 950gms thrust. 5.65g/w

So it's reasonable to expect 5g/w.

Here's a different example.
T Motor AS2304 1800kv. 650gms thrust on a T Motor 8x4.4 prop drawing 178w, 15.5a at about 11v.
That's only 3.65g/w.
But it's 650gms thrust from a motor that weighs only 20gms!

Thank you for all the help. My thrust stand setup is actually pretty similar, I think I even have the same/similar weighing scale.

For the props I found aeromodelindia sells Gemfan props (which are supposed to be similar to APC from what I've heard) and xyzhobby ABS EMP propellers. Are those sites reliable to buy from?

RCDHAMAKA has APC props.
Aeromodelindia/ Sharma Model Aero is India's oldest existing hobby manufacturer
XYZ also has a tach worth getting.

Please consider posting a build log of what you are planning/ working on.

Regards
Iyer

So, I tested it again with the new ESC and with the propeller flipped (the raised text facing the motor), it produced 1350 grams of thrust while drawing ~290 watts.

Quote from: GlamHawk on December 18, 2023, 02:23:52 PM
So, I tested it again with the new ESC and with the propeller flipped (the raised text facing the motor), it produced 1350 grams of thrust while drawing ~290 watts.

2s or 3s? And which prop?

http://www.dys.hk/product/D3536.html

Here is link to the datasheet of the motor on the DYS website.

Quote from: pnkyjs on December 19, 2023, 03:58:50 PM
http://www.dys.hk/product/D3536.html

Here is link to the datasheet of the motor on the DYS website.

@pnkyjs,

That stage was crossed earlier in this thread, in reply #6 

" 1. Your 3536-5, 1450kv. 700gms, 400w. 1.75gms/w
2. DYS claim for same motor. 1450gms, 655w. 2.2gms/w (This is very low performance)"

Regards
Iyer

3S with the same orange composite 9x4.5 prop.