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Old Nov 02, 2012, 02:05 AM
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My test stand is a frame, with no moving parts at all - it just sits right on top of the scales. Just zero it before a test, and off it goes..... zero friction or error possible.

And to check scale accuracy, we have two other digital scales around. (up to 10Kg types). So I just throw some batteries on them all to compare a few weight areas.
All three a DEAD EQUAL... not close.... exact.
Which makes me think modern digital scales must be very easy for them to get right... accurate. Some form of digital sensor (IC??) that means it is easy to replicate that accuracy.
I am not sure how they make them...... (I should bust one apart and see!! LOL)
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Old Nov 02, 2012, 02:27 AM
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Originally Posted by PeterVRC View Post
You would HOPE that if everyone used vertical stands they would have to be the same??
Even vertical stands have variances. I 've seen the efforts of a guy in this thread who had the fan mounted too close to the "bottom" and the airflow was getting disrupted.
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Old Nov 02, 2012, 03:29 AM
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Originally Posted by PeterVRC View Post
My test stand is a frame, with no moving parts at all - it just sits right on top of the scales. Just zero it before a test, and off it goes..... zero friction or error possible.

And to check scale accuracy, we have two other digital scales around. (up to 10Kg types). So I just throw some batteries on them all to compare a few weight areas.
All three a DEAD EQUAL... not close.... exact.
Which makes me think modern digital scales must be very easy for them to get right... accurate. Some form of digital sensor (IC??) that means it is easy to replicate that accuracy.
I am not sure how they make them...... (I should bust one apart and see!! LOL)
Just for due diligence, is there a stock 70mm fan\motor you can test with?

tia
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Old Nov 02, 2012, 03:55 AM
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Originally Posted by PeterVRC View Post
My test stand is a frame, with no moving parts at all - it just sits right on top of the scales. Just zero it before a test, and off it goes..... zero friction or error possible.
My sled is too problematic to mainain it in a reliable state. I want to go to a vertical one as well.

Can you post a picture please.
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Old Nov 02, 2012, 04:13 AM
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I will go out later and take a pic. I think I had it in here somewhere once before.
VERY simple to do with some bits of wood, LOL. Much easier than a sled.
It can take 70mm and 90mm fans, of any design, housing etc.
It is mounted onto the scale "permanently" using double sided tape.
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Old Nov 02, 2012, 05:54 AM
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EDF test stand:

1) Made from 19mm MDF panel wood and some bits of pine (35x90 and 90x19)
Though you can use all sorts of wood types really.

2) The EDF 'blocks' have multiple hole positions, so it can open out to suit numerous fan sizes - and you can just drill some more if you ever need more!

3) A $20 digital kitchen scale attached underneath with double sided tape. One with a slide-out display so it could come forwards into better view, So start any project with an idea of what scales you will use, and to be sure you will be able to read them still.

4) The power meter, kv meter, and scale readout all group out at the front for easy reading - even if the "blast shield" is up. LOL

5) The ESC uses velcro to mount onto a side panel, so that it gets some ariflow for cooling. (not much but enough)

6) Two screws for mounting a "blast shield" to shield you from any exploding fan!! LOL. Well, it is only lousy 3mm plywood - but ply is quite a strong construction, and very energy absorbing too. So I expect it will stop any fan blade parts fine. Errr, fine enough....

7) Capability to be used for 'other' measuring tasks.....

The camera makes some pics 'fish eyed' and make straight lines look askew. Rest assured it is all 'square', hehe.
...
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Old Nov 02, 2012, 05:58 AM
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Aircraft thrust test stand:

Same EDF test stand with the patented "Aircraft clamperer and balancer assembly". LOL

This "addon" just bolts onto the EDF Test Stand and can hold an EDF aircraft of almost any design while you thrust test it. Vertical instead of 'friction adding horizonatal".

...
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Old Nov 02, 2012, 06:48 AM
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Peter,

very informative. Thanks!
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Old Nov 02, 2012, 08:12 AM
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My thrust tester is MUCH less advanced but would probably do for most:

Get a kitchen weight. Set the plane on it's nose, hold the plane so it doesn't fall over. Hit full throttle
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Old Nov 02, 2012, 09:21 AM
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I do that for 'simpler' aircraft. Not worth setting up for those.
Prop aircraft I do with a sash and digital fishing scale, pull mode.
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Old Nov 02, 2012, 02:03 PM
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Originally Posted by beamen View Post
My thrust tester is MUCH less advanced but would probably do for most:

Get a kitchen weight. Set the plane on it's nose, hold the plane so it doesn't fall over. Hit full throttle
Bingo -- esp when usually all I need to do is answer the question "Do I have greater than 1:1 thrust for this plane's weight?" (a weight, btw, that was measured on exact same stand just prior to hitting tare)

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Old Nov 02, 2012, 02:39 PM
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How much typically will the in-plane thrust differ from the open-air thrust as you read using your testing apparatus? Of course it depends on the restriction of the air channels in the plane, but a guesstimation would be welcome.
I'm looking to replace a 70mm 5 blade fan w/3300kv motor that generates 1.2kg thrust in -plane. I see HK has RC lander-ish allor fans that report a 1.7kg figure (not sure how accurate this is). Trying to figure if it is worth taking the chance to buy them.
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Old Nov 02, 2012, 04:07 PM
chuck
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Originally Posted by erh7771 View Post
Not if it's an outrunner, plenty people running the 2100kv on 6s...don't use 65c packs...extra .25 - .50 volt hurts stuff...a lot of stuff.
really ? didn't hear to many pipe right up. i guess all the people that are using motors twice that heavy just need the dead weight . an extra 1/2 volt at 22v is not going to make or brake it unless you are already in the efficiency pit.

chuck.
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Old Nov 02, 2012, 05:26 PM
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Originally Posted by TheCure View Post
How much typically will the in-plane thrust differ from the open-air thrust as you read using your testing apparatus? Of course it depends on the restriction of the air channels in the plane, but a guesstimation would be welcome.
I'm looking to replace a 70mm 5 blade fan w/3300kv motor that generates 1.2kg thrust in -plane. I see HK has RC lander-ish allor fans that report a 1.7kg figure (not sure how accurate this is). Trying to figure if it is worth taking the chance to buy them.
Sometimes it can be exactly the same if the ducting flows well enough, I have had quite a few models that produce the same thrust as the fan did on the bench. Often though the intakes are messy or restricted and will cause the fan to starve and drop in thrust. This is all based on static measurements mind you.

The 1.7kg they quote looks like a peak value only, if you watch the videos of the fan, 1.5 or so is the stable thrust, and you have to consider the weight of their fans too, as a German made Wemo Minifan and an HET 2W18 will produce 1.5kg thrust at 800w and weighs a lot less, better engineered and better quality, will run flat out all day long.
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Old Nov 02, 2012, 08:32 PM
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really ? didn't hear to many pipe right up. i guess all the people that are using motors twice that heavy just need the dead weight . an extra 1/2 volt at 22v is not going to make or brake it unless you are already in the efficiency pit.

chuck.
Nah, it's like a 4 banger that's been turbo charged and is putting out 300hp...you know there's little room before internals on the motor has to be changed so you''re pretty much pushing the motor to it's limit which I like....

I would hate to think I have 3/4lbs of thrust left on the bench when I'm flying a 70mm

With other motors you have what I call head room, they'll absorb the extra .14 - .25 volts per cell that a good 65c packs puts out and does it without whining....where the 12usd motors from HK wont do such for long...going back to ICE analogy the HETs are 6 cylinder engines and will put out more RPMs for same octane gase and even more with higher octane gas...where the other internal combustion engines will just burn up but for budget reasons they're good for what they cost.

The HETs also put out more RPMs with change of timing or pwm that doesn't heat up the ESC etc...
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