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Old Jan 19, 2009, 04:47 PM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
2,732 Posts
My thrust stand

I built this yesterday to test thrust from a hextronics D1811-2000 motor. I wanted to check given thrust using a GWS 5x3x3 prop on a 3s lipo as well as 2s. Wondering if perhaps someone else could confirm my results for me. I showed about 3.5 ounces at half throttle on 2s and showed 6 ounces on the 3s. At full throttle on 3s it started at 10 ounces and fell off to 9.3 after 3 seconds. Someone mentioned that my test rig may not be accurate. Your thoughts are welcome and if I did build the test rig wrong please correct me.
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Old Jan 19, 2009, 10:20 PM
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rgoble's Avatar
Dayton Montgomery, Ohio, United States
Joined Sep 2004
259 Posts
Quote:
Originally Posted by peterangus
Robert

The extensive tables on each motor page are not necessary!

If you have a props page [as #102], then each prop will have only one line entry, instead of dozens of lines on different motor pages. And any added props will relate to the motors with no further effort.
I realize that its hard to find exactly what your looking for in some of the larger tables. I have a way to allow you to quickly sort, filter, and even break the table across multiple pages. The only reason I don't have it enabled on the motor pages now is because of size issue. There just isn't any room for the column sort images with the current layout.

I know that it is possible to calculate the RPM, and current for a given prop, volt, motor combo. I believe Drive Calculator and some others do this. I have not had time to research those formulas yet but it is something I plan on looking into. I think it would be nice to provide the users with an estimate for props that were not tested.

Robert
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Old Jan 19, 2009, 10:32 PM
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rgoble's Avatar
Dayton Montgomery, Ohio, United States
Joined Sep 2004
259 Posts
Quote:
Originally Posted by CapMike
I built this yesterday to test thrust from a hextronics D1811-2000 motor. I wanted to check given thrust using a GWS 5x3x3 prop on a 3s lipo as well as 2s. Wondering if perhaps someone else could confirm my results for me. I showed about 3.5 ounces at half throttle on 2s and showed 6 ounces on the 3s. At full throttle on 3s it started at 10 ounces and fell off to 9.3 after 3 seconds. Someone mentioned that my test rig may not be accurate. Your thoughts are welcome and if I did build the test rig wrong please correct me.
I have data from Bruce Abbot on my site showing him testing that motor at 7v with a GWS 5x3 prop. Its obviously not the same as what your using but might help give you a ballpark idea.
http://www.flybrushless.com/motor/view/431


As for you test stand other will be more helpful then me. However I do know that on Dr Kiwi's setup he runs it as a pusher, with the scale behind the motor. I think the problem with setting it up in tractor mode has to do with the mount messing with the airflow and giving you inaccurate results. Also I think the distance between the pivot point and the motor, and the pivot point and the scale have to be equal or else you will get inaccurate results.

Robert
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Old Jan 20, 2009, 05:08 AM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
2,732 Posts
Quote:
Originally Posted by rgoble
I have data from Bruce Abbot on my site showing him testing that motor at 7v with a GWS 5x3 prop. Its obviously not the same as what your using but might help give you a ballpark idea.
http://www.flybrushless.com/motor/view/431
Robert
Robert given the test results shown as follows on 7 volts my results could not have been too far off then. GWS EP 5x3 1 7 2.36 16 10830 0.0 107 3.77 with 3.77 ounces of thrust on a 2 blade. This option then is a viable solution for a scale model turning a 3 blade prop. I will verify that my pivot is central and rerun the test. I really dont think it would matter whether the mount is in pusher or tractor config. Given that we would have the nose or nacelle patially blocking airflow.
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Old Jan 20, 2009, 08:12 AM
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Chattanooga, Tennessee, United States
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Last edited by Dr Kiwi; Feb 13, 2009 at 08:44 PM.
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Old Jan 20, 2009, 08:15 AM
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Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
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CapMike - it is not much that there is hindrance to the flow (just as there would be with a snub nosed plane) but that, as the efflux from a tractor prop hits the vertical arm of the stand, it lessens the downforce on your scale (as the vertical arm is pushed back, it is lifting your "pressing arm"). I tested this idea and found that the effect (reduction in measured thrust, "tractor < pusher") was relatively minor with large props (maybe 5% or so) but far greater with smaller props (10% or more).
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Old Jan 20, 2009, 03:40 PM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
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Thanks DR Kiwi. wondering if you might confirm my thrust measurement.
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Old Jan 26, 2009, 02:09 PM
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Tom Frank's Avatar
United States, MA, Walpole
Joined Dec 2003
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Quote:
Originally Posted by CapMike
I will verify that my pivot is central and rerun the test. I really dont think it would matter whether the mount is in pusher or tractor config. Given that we would have the nose or nacelle patially blocking airflow.
If the length of your arm from prop shaft centerline to the pivot centerline is more or less than the distance from the pivot centerline to the midpoint of your scale contact piece, your measurements will be wrong, but they are not wasted. Simply multiply your measured thrust by the ratio of the two arms.

e.g. Actual thrust = measured thrust * horizontal arm length / vertical arm length. No real need to modify your rig or re-run the test unless you want to.

The two arms should also be at a 90 deg. angle for this calc to be totally accurate, but a few deg. off wouldn't make any noticeable difference.
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Old Jan 26, 2009, 02:13 PM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
2,732 Posts
I have done nothing more with the test rig. I used the data from the site in motocals and it shows thrust as being 9.9 ounces. This seems to be close to the value that I showed from my test. I am satisfied with this result.
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Old May 10, 2009, 10:08 PM
Unregulated User
East/Central Florida
Joined Feb 2009
176 Posts
I also registered too but have not been verified for my account. I'll try again please see if I made a typo. Thank you for all your work, very impressive. What do you do with all the motors?
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Old May 10, 2009, 10:32 PM
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Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
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Many are loaners.... though I do have quite a collection of extras, some of which I sell off at modest prices to fuel the hobby!
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Old May 11, 2009, 10:00 PM
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Dayton Montgomery, Ohio, United States
Joined Sep 2004
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MIJohn,

I thought I had all of the problems with the registration worked out but I guess not. I activated your account for you so you should be able to login now.

Robert
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Old May 12, 2009, 05:22 AM
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Fourdan's Avatar
Antony (France)
Joined Sep 2003
2,965 Posts
Quote:
Originally Posted by peterangus
Dr K

I produced the attached plot using a HUGER wind meter.

As you see, the velocity varies from point to point. A reasonable average value to record would be 95% of the highest value that can be found.

Best if the prop is tested in "pusher" config, with no centrebody to confuse things.

The presence of the meter should have zero effect on the upstream flow [ie, upstream of the meter].
Hi Peterangus
For your graph post #99 (excellent), did you recorded the rpm for the MAS 12x10 folding ?
Regards
Louis
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Old May 12, 2009, 10:02 PM
just Some Useless Geek
Chicagoland
Joined Oct 2008
2,539 Posts
Just a note: I am working on the XML Schema for the motor database. It appears that we need one for the props, too, since they are a vital part of testing in the Real World. It isn't a bad idea to have a prop database anyway, considering all the grief we have trying to hook small electrics up to the right prop/adapter/prop saver/shaft/yada yada yada.
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