Prop balancing tutorial

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orcinus
Member
Posts: 36
Joined: Thu Jan 23, 2014 11:03 pm

Prop balancing tutorial

Post by orcinus » Sun Jan 26, 2014 11:05 pm

Here's a little trick for balancing really tiny propellers that i've picked up on an RC forum once...

STEP 1:

Image

Gather all the necessary tools:
- Vernier caliper
- sewing needles in as wide a range of sizes as possible
- two magnets (the two white cylinders in the photo - you can use any suitably small magnet with at least two flat surfaces)


STEP 2:

Image

Find a needle you can barely get through the propeller shaft hole. If you're worried about loosening up the hole too much, or can't find a needle of a suitable diameter, just find one you can put the propeller on snugly with the pointed tip sticking through at least a few millimeters (as depicted).

Note: The needle MUST be straight! Or as straight as you can find.


STEP 3:

Image

Put one magnet on each caliper jaw as depicted - try to get them as level as possible and as stable as possible.
Now comes the fun part.


STEP 4:

Image

Put the needle with the propeller between the two magnets and let it stick to one of them with the pointy tip.


STEP 5:

Image

Close the caliper jaws slowly until the needle "snaps" to the opposite magnet.
When it does, stop closing the jaws and open them back up a VERY VERY tiny amount.


STEP 6:

Image

Now carefully nudge the needle back towards the pointy end magnet. It should snap there and stay there.
If it doesn't, open the jaw a slight bit more.


Start balancing!

The needle should now be suspended between the two magnetic fields with extremely low friction (because it's resting on the pointy end, with minimum force). The friction will be so low that even your normal breath might cause the propeller to rotate. Which is exactly what we're after.

Find a room with the least amount of draft and start balancing!

I recommend using tiny dots of nail polish or paint, as the Crazyflie propellers are simply too tiny and finicky for masking tape.
Last edited by orcinus on Sun Jan 26, 2014 11:07 pm, edited 1 time in total.



orcinus
Member
Posts: 36
Joined: Thu Jan 23, 2014 11:03 pm

Re: Prop balancing tutorial

Post by orcinus » Sun Jan 26, 2014 11:06 pm

PS: Apologies for the crappy photos, the room wasn't lit very well and it's nighttime. And i'm too lazy to get my DSLR out.

PPS: If any part of the procedure is unclear, let me know and i'll try and shoot a movie of the whole thing.

tobias
Bitcraze
Posts: 1880
Joined: Mon Jan 28, 2013 7:17 pm
Location: Sweden

Re: Prop balancing tutorial

Post by tobias » Mon Jan 27, 2014 9:37 am

Thanks a lot for the these great step by step instructions. Is it OK if we copy this to the wiki? We can create a wiki account for you as well if you want.

orcinus
Member
Posts: 36
Joined: Thu Jan 23, 2014 11:03 pm

Re: Prop balancing tutorial

Post by orcinus » Mon Jan 27, 2014 2:30 pm

Sure, feel free to copy.
I still need to figure out a sensible / consistent way to do chord-wise balancing (edge-to-edge).

Balancing the cf props this way often gets them to a state where they'll settle horizontally, but prefer one horizontal position over the opposite one.

orcinus
Member
Posts: 36
Joined: Thu Jan 23, 2014 11:03 pm

Re: Prop balancing tutorial

Post by orcinus » Mon Jan 27, 2014 5:24 pm

Funny thing...

At this size and with extremely low friction, static electricity starts becoming a problem.
I've dropped a prop on a carpet and it accumulated a static charge, after which the presence of my fingers would start attracting the propeller :lol:

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