Small LRK outrunner - Page 2 - RC Groups
Thread Tools
Dec 28, 2003, 04:57 AM
Registered User
billystiltner's Avatar
You are right Gordon.
I should have reworded my statement
to something like

The arms must be equal length to get 1 to 1 thrust measurement.

I'm glad you caught it. It's nice to have poeple
catch my mistakes and not get upset about it.

Sign up now
to remove ads between posts
Dec 28, 2003, 10:07 AM
Registered User
Dave Wulff's Avatar

As a printer, I would avoid using paper as a calibration standard. Paper is like a sponge when it comes to humidity. Depending on conditions in the room, it can take on or give off a relatively large amount of moisture very quickly. Much better to use something like brass and have someone with a lab quality balance weigh it for you, that way it will be stable.

Dec 28, 2003, 10:54 AM
Registered User
mmormota's Avatar
There are cheap digital kitchen scales, they fit well to this application.

RPM measurement with PC (no additional hw): there is a free oscilloscope program "Winscope", it uses the soundcard and has fft function. Put the microphone near to the side of the propeller circle, the pressure waves are clearly visible. Switch to fft, it gives the result in Hz, just multiply by 30 to get rpm.
Dec 28, 2003, 11:02 AM
Registered User
billystiltner's Avatar
You are right.
My apartment stays very dry most of the time.
All of our air conditioning systems were upgraded last year and
as long as the heat or air conditioner or fan comes on once in a while the relative humidity stays betwen 35 and 50. Unless of course it is raining and it jumps up a bit I think. So as long as I do my calibration when it is dry I guess it is ok to use paper. But I do need to get a standard weight. I should probably dope my beam as well to keep it from gathering moisture. I use 24AWG copper wire from network cable for the weights but I have noticed that oxidizes after a while and I guess it gets heavier a bit with oxidation. I think silver would be better as it oxidizes slower. I think the copper wire varies from one brand to the next how much actual copper is in the wire or either the thickness varies because I have noticed that the same length of 24 AWG from 2 different Network cables weight slightly different.
Thanks for the info Dave. How much weight of water do you think 1g of printer paper would draw up with a rlative humidity between 35 and 50. Would it vary that much between those 2 points?

Dec 30, 2003, 07:28 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Mike, what magnets did you use? Strength/quality/source?
Dec 30, 2003, 07:51 PM
For Sale-everything over 250 g
I cut the magnets from scrap where I work. They are neo. but I'm not sure what strength. I do know that they are not N45 they are weaker, but not much.
Jan 02, 2004, 03:14 AM
Registered User
How do you cut the magnets? I have a slab of neo from a hard drive , its on the head control .
I either need another 3 to make a plate type brushless or cut it up to use in smaller motors and actuators .
Last edited by clipclop; Jan 02, 2004 at 12:22 PM.
Jan 02, 2004, 08:21 AM
For Sale-everything over 250 g
There is no easy way. We have a diamond saw that cuts under a cooling fluid. It would be very dangerous without the right equipment. The dust is very flamable and the magnets can be ruined if they get too hot.
Jan 02, 2004, 08:37 AM
Registered User
Thanks, looks like I have to build a diamond saw !
They not to dificult , I have seen saws used for cutting rocks .
look pretty simple to make just need a tray to hold water under the blade a small pump and a drive motor to work it all
4" blades are not expensive .
Jan 02, 2004, 09:44 AM
Registered User
billystiltner's Avatar
I have not cut the big magnets in hard drives but
have scored small magnets then snapped them and grind with dremel. You have to be very careful and only touch the magnet to the stone featherly or it will get hot. I guess if you can hold the magnet with your fingers then it should be cool enough.
Watch out for the dust though wear a mask and it's robably a good idea to grind outdoors some of the peices spark like sparkler fireworks if you grind too quick.

Jan 02, 2004, 09:54 AM
For Sale-everything over 250 g
You decribed our saw! It is about a 4 inch blade and has a winshield washer pump in the fluid. The cooling fluid is blue and is water based. The blade is about .010 inches thick.
Scoring and grinding works too. As long as you can hold it, it will have stayed below the temperature where it starts to lose power. If it is from a hard drive it is probably plated. Remove the plating before scoreing.
Sep 13, 2004, 01:43 AM
Registered User
Mr DIY's Avatar
Mike .. saw your enquiries on Yahoo.

Question ... how have you got your motor wired up. Star or Delta?

Sep 13, 2004, 04:25 AM
Registered User
fantastic job. Now we should all vote and convince Castle to make a 1 gram controller.

Sep 13, 2004, 07:24 AM
Registered User
Originally Posted by mcross
I had to machine all the parts except the stator stack. I have one of those mini lathes from Harbor Freight. The original motor had windings on the stator and rotor so I could only use the rotor. It weights 3.9 grams.
Wow....could you post how you machined those parts? I've got a Unimat 3 set up for lathe and milling but have no idea where to being for adapting these CD motors.


Sep 13, 2004, 07:25 AM
For Sale-everything over 250 g
I'm working on this motor again, here is part of my ? to the Yahoo LRK group.

"Thanks Ron, I really don't know what else to try. This is the motor I was
working on the end of last year and am getting back to it now. There are
no shorts, phase to phase or phase to case. The controller is not intended
for model use but works on inrunner brushless motors very well. I did have
it running but at 2.5 volts it was drawing .75 amps. RPM of the motor was
the same as the frequency of phases so it wasn't running like an LRK. I
have a Pheonix 10 but haven't tried it yet.

I know of someone else with a small LRK that is having the same problem.

Anyone have any ideas?"

I've only tried it wired star, I have all 6 wires coming out so I could try delta. I was going to rewind it with all teeth wound but decided to wait.

A 1 gram controller would be great but I think an Rx with built in brushless controller would be better. I do have control chips that will run BLDC motors but only on-off or analog voltage control. They weight about 1.5 grams.