Build thread: submicro brushless motors

[nachman]

Shagrug
  Your work is amazing!  I want to give it a try and also built one of those tiny single phase brashless motors. I've orderd the Alegro chip from DigiKey and I'll probably start with a magnet taken from the 3.2 pager motor. Maybe I've missed reading it, but where can I buy the  ring magnet you've used on the smallest motor you've built, the 0.5mm x 1mm dia ?
 Is there a way to have these type of motors turning both direction for use in a micro servo? Will using two chips on one motor do it ?

[shagrug]

Hello nachman-

     Thanks-  I'm getting most of my magnets from George Mizzell (Engineered Concepts), also known as "Supermagnet Man" on the internet. The link to the ring magnets is here- but be sure to look at the cylinder shapes as well. And, only the ones magnetized across diameter will work.
http://www.supermagnetman.net/index.php?cPath=41

      The 3.2 and 4mm pager motor magnets are easier since the shaft and bearings are reuseable. Cutting the magnets down smaller usually breaks them or chips the edges badly.

      There has been some discussion about using these motors on servos here:
http://www.rcgroups.com/forums/showthread.php?t=1166672

      It might be possible to reverse the direction, by using two chips wired to the same coil or by a switching circuit. But the low startup torque would require a lot of gear reduction or a much larger magnet to make it work well.

      I'm hoping Helmut will get the new circuit worked out  for a 100% duty cycle motor- this will boost power output. The startup torque will probably still be too low for servos though. I'll keep working with the A1442 chip as well, I really like it.

     

[nachman]

Wow, great site for magnets. Thanks. I've placed an order for a bunch of them in several sizes. Just have to wait now for everything to arrive. I'll post my attempts.

[shagrug]

      I finished the aforementioned six inch ultimate.....

      I'll post most of the photos in a seperate rcg thread, so as not to clutter up this one:

http://www.rcgroups.com/forums/showthread.php?p=14185430#post14185430

[shagrug]

      A vid showing the controls working for Jin.....

six inch ultimate biplane - testing controls

[zenoah]

Hello,

I'm new too the world of extreme small aircrafts, but I would like to give them a try, starting with making my own actuators. I also like to mess around en build my own tools, so I want to build something like your coil winder.

but I don't really know what you do too that poor little calculator and with than mechanical switch...
could you tell me how to do that? or is there perhaps a tutorial somewhere? I think a lott of people are interested in the ins and outs of youre counter!

(I hope you can forgive me for my basic englisch, I have to practice a bit more...)

Grts
Jacar

[Kerbob]

  LOVE that new Bipe Shagrug! 

Can't wait to see and video it flying too.  Are you going to hook up the upper ailerons?  That's going to add at least another 0.02g I think. 

Great video with the dime.. very clear to those who might never believe you could make a 4 channel bipe that weighs the same as a dime.

[shagrug]

Hi Kerbob-

      Thanks,... I'll just use the bottom ailerons, I don't care about aerobatics with this one. It's more about the large wing area to carry the weight. If it has slow level flight and can rog I'll be happy.


      Hello zenoah-    Glad to help if possible.... Let me see if I can explain the calculator-counter setup more.
      I know the keypads vary from model to model, and the calculators with big keys might be easier. Inside the case, you need to find the circuit wires between the "=" (equal) key and the main ic board. It will be just two conductors, the = key is the switch that connects them when pressed. These two wires (or copper strips) are what you need to connect to-then  they are hooked up to your winder spindle switch. The external switch can be a roller, pushbutton, or magnetic reed- anything that will close the circuit each turn of the spindle/mandrel. I used a roller switch with a cam to press it each revolution. (see photo below) The calculator I used was very cheap, the keypad circuits are printed on a plastic film- so I made my connections at the top where the plastic meets the main ic board. Understand? If not I can draw you a diagram.

      And you don't have to use a counter to wind coils, just measure and cut  the length needed for the resistance requirement. That's how I used to do it, since I was only making one or two at a time. The counter just makes it easy to repeat coils and use bulk wire spools.

      I'll make my next  post with more advice and tips on making the motors (and actuator coils)  It might be of more help to you, nachman or others wanting to try making some.
     

     

[shagrug]

      I got most of the design for my winding machine from this vid, by David Dewit. It shows his step by step process making actuator coils.

http://www.rcgroups.com/forums/showthread.php?t=850115#post9569151

     There is more good info in this thread on coil winding. Since the motor coils are so similar to actuator coils, it is worth a look:

http://www.rcgroups.com/forums/showthread.php?s=&threadid=143929

      The only thing I didn't like on David's setup is the long distance between his fingers and the mandrel (because of the CA glue pan inbetween), I wanted my fingers closer to guide the wire around the bushing pin. And I wanted slower speed, to try and keep the winds neat. I usually try to get the first two or three rows of wire on perfect (no gaps or overlaps), after that I usually get a few off track. Just keep feeding the wire back and forth at a even speed, and add a drop of CA every 3 or so layers of wire. I've gone back to using CA on all my coils now that I have the teflon heatshrink over the center, it's a lot lighter than the epoxy.

      Soldering is one of the hardest parts to making the motor- the A1442 is so tiny, and the wires so fragile it may take more than one try. If you don't have a sharp point on your soldering iron you can wire wrap fasten a sharpened brass or copper rod (sewing needle size) to the tip of the iron. I've done that in the past, it won't last long before the tip burns up though

      I also recommend using a steady rest for the soldering  iron barrel, like it the photo below. Just a half mm wobble when soldering the ic chip or wires can make a mess of things- the rest will improve your aim a lot. In the photo I already have the magnet in the coil- that is backwards, you want to solder all the coil connections before adding the magnet and  shaft. If the magnet is there, it will pull on the soldering iron tip and spoil your aim.

      I usually don't use any flux, I just tin the A1442 pads and wires first with solder. I use Radio Shack part no. 64-013E silver bearing solder (.022" dia. 62/36/2) for most everything. The insulation can be easy or hard to remove from the magnet wire- I've used acetone on some (dipping melts it right off), but usually just solder since it tins at the same time.  I  had to use flux to tin the very tiny watch coil wire, it was very hard to do. 

      As soon as you finish taking a new coil off the mandrel you will want to check the ohm reading. I leave the coil wire 2 or 3 inches long at first- then retin them close to the coil when I solder it to the chip. Then clip off the end. I usually hookup the coil wires to the chip first, then the power supply wires. For my test motors I just used a heavier gauge magnet wire to power-  litz wire is better if you have it.

[zenoah]

Hello shagrug,

thank you for the extra info! I missed the part about the "=" button at first, but now I have a nice little calc with a rollerswitch attached! I've also gathered some old relais and "stole" their wire! I now have 0.2mm, 0.15mm, 0.1mm and something like 0.05mm but I don't thrust my digital vernier with that size... so I only need something to fix my mandrels in... (for actuator coils I'll be using a turned down candle, melt it off in boiling water an you have a perfect coil)

when I finish everything I'll try to post a picture if anyone is interested?

Grst
Zenoah.

[shagrug]

Hi zenoah,

      Glad to hear you have it working. I know of the candle wax mandrel method, it works well. I'd sure like to see whatever you make, post it here if you like.

      Someone asked me recently what the counter is for- it works like this: Let's say you need a 60 ohm coil from a given spool of magnet wire. First you would figure the resistance per foot of wire by measuring with a ohm meter. Then cut a length of wire  to the number of feet needed to make the first coil. Put this precut length on your winding machine- and use the counter to count the turns used to make the coil. Now you can wind the same coil over and over again from a "bulk" spool of wire- saving the time of having to measure the length in feet.

      I've been busy the last few days with other projects (like the Guillows triplane) but will be back to to motors soon as I have time. I have some new ideas to test and materials to work with- like in one photo below.

      I've been doing some trading of materials with Veteran (on the RCG motor thread), he sent me some very nice brass watch/clock gearsets in just the right sizes for these motors. Also some equally nice 25mm cf props I can use for direct drive, 2x3mm magnets, and some other good useful parts. I'm really looking forward to using the gears and props.

      I've been thinking of milling or lathe turning the didel-plantraco plastic gears I've been using to half-thickness to save weight, and still might try it. I've also been looking at the plastic servo gears used on the parkzone/spectrum bricks- they are a lot smaller than the plantraco and could be used on a motor easily. I've got a dead brick (in the photo) that I may try the gears from- they look the right size for a 2.5mm magnet motor.

[shagrug]

Today makes sixty days/2 months that the big 4x5mm magnet motor has been sitting in a box, with the magnet attracted directly to the a1442 chip.

So I did some new tests tonight to see if the chip has been damaged by magnetism over time, and duplicating the vid clip test I did before (bottom page 1, on 1/3/10), so you can see the difference.

In this new vid it's about 300 rpm slower at 2.4v, and 100 rpm slower at 3.7v.. On a few other runs it was always within 100 rpm's either way. (consistantly slower, and normal to vary like this)

So it looks like the chip is being damaged with time.... I'll retest it again in another month or two, and see if it loses more speed.

4x5mm magnet brushless motor retest 3-3-10

 

[Kerbob]

I've been following the RCGroups sub-micro brushless motors thread HERE since I found the thread.  I've really enjoyed reading the progress by the sub-micro scientists like Helmut-Schweig and many others there. 
 
So, it looks like the chip's magnet position sensor (Hall sensor) is being damaged by the strong magnet over time. You could move it, but it still has to be in the right position to determine magnet position and with a motor that small, you have very limited options.     Or, you could go without the hall sensor and start the motor manually, but it seems like it would also lose torque with that.
 
You also mentioned a heat issue in some of your posts.  Maybe, the loss of motor power is due to the magnet is losing some of its magnetism due to the high heat?  I don't know what the heat rating on those magnets are.  Maybe, I shouldn't be dabbling in this space where I have extremely limited knowledge..   but.. its fun.

[shagrug]

Hi Kerbob,


      After the recent posts in the RCG thread, I'm not so sure the chip is being damaged. If it is happening, there is only a tiny decrease in performance. (less than 1%)

      I'm sure heat is not the problem, since I don't get the motor more than warm. And that heat seems to be just in the chip and coil, the magnet stays cool.

      Last week I made a new test motor using the 2.5mm square magnet and a adjustable timing ring-collar. I've spent several hours running it now, and I'm happy with the results. I was thinking the motor would improve with the timing advanced, but it seems not to matter much.

     The friction fit sliding ring is made from a strip of copier paper, wrapped 3 turns-layers on a teflon rod and glued with thin c/a. Once dry it slips off the rod easy, and works fine for the ring. As you can see in the photos, you have to leave plenty of wire so the coil can slide back far enough to get the magnet and shaft in.

     The motor has a 24 ohm coil, made with the .05mm diameter wire, 204 turns- and this time using a .020" drill blank shafting rather than stainless hypo tube.

     It's been on my mind to use drill rod or blanks for shafting, even more so since I pulled apart another test motor (no.6) a while back and saw a lot of wear on the stainless tube, The tube had a lot of wear considering the low run time- not a step in the shaft, but not far from it. The steel drill blank material is hardened to where that won't happen, and rust is the only problem to worry about. The fit on the bearings is much closer too, not as loose as with the hypo tube. I had to run this motor for over a hour at low voltage (1.6v) to break it in, now the bearings feel just perfect.

     The timing test results were interesting- I see at most, a 100 or so rpm gain by advancing the timing 10 degrees or so. This is running at both 2.4v and 3.7v...10,600 and 13,500 rpm's respectively. The ring position was changed with the motor running at the set voltage, back and forth. I went as far as 30 degrees in both directions- the motor still ran but speed drops off some once you go past 10 degrees or so, either way. (retarded or advanced) As long as it is within 10 degrees of zero, it runs fine and at full speed. The gain by advancing it is so slight, it is not worth it in my opinion. My tach may have been off by this much, mabe there is no difference at all. Best to glue the chip in the center of the coil, as I have been doing. Of interest  too is that it will run normal with the chip at 90 degrees to the coil- and again there will be a slight loss of more than speed 10 degrees each way past this point. 

I've figured out a good way to get a press fit of the magnet on the drill blank shaft. I cut a notch in the shaft at the magnet position with a grinding wheel, then fill the notch with soft solder. Just enough to fill the gap, with a slight hump- this gives the tight fit. A long section of turned down bearing material is used as a tool to press it together inside the coil. No glue to get in the bearings, and the motor can be taken back apart again

To solder steel and stainless steel, I use the stay-clean brand flux. I started using this flux about 20 years ago for soldering various metals, it will work where many others won't. It has a hign content of hydrocloric acid so be careful with it if you should use it.

Also I've gotten some new wire to experiment with, from a e-bay seller at this link:
http://cgi.ebay.com/48-AWG-GAUGE-MAGNET-WIRE-6400-FEET_W0QQitemZ220548527407QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3359b7752f
He has several other sizes available on small spools, and he is a fellow RC flier as well. The wire is good quality, not brittle and easy to tin. I've ordered a couple more spools already in thicker gauges.

[shagrug]

Hello All-

       Last night I finished test motor no. 10, and it is another good learning experience. It is very close to the 4mm pager motor in power, only 100-200 rpms slower at 3.7v. (vid of the pager on page 1)
     
      The coil is the main difference- this one being 22.5 ohms and wound from #42 gauge magnet wire. (from one of the spools in my last post) I first wound a 24 ohm coil but broke one wind when getting it off the mandrel. It had the problem of having so much wire it was stacked up over the teflon end washers. So I made the next one a bit smaller- but it is still a lot of copper mass. So much that now the coil (.12g) weighs more than the magnet (.08g) Total weight of the motor is .22 grams minus prop. The 4mm 13ohm pager motor weighs about .64 grams.

      So now I have about the same performance as the pager motor in a motor that weighs about one third as much- also using only about half the current. At 3.7v the pager draws 220ma compared to 120ma on the brushless. The smaller lipos will like that. No problem with heat, even running at 4.2v the chip and coil are getting warm but nowhere near hot. That kind of surprised me, I expected this lower ohm coil to heat up more. The more I run it the better it runs, it is still breaking in the bearings. It has over 4 hours run time now and keeps getting faster. I also have not oiled the bearings yet, that may help too. 

      The new drill blank shafting and closer fit bearing seems to help, I feel and hear less vibration. Same for the timing ring motor, it seemed smoother too. So I am done with stainless tubing for shafts. I used a bit of stainless heavy wall tube for the magnet spacer this time rather than brass, using CA to glue the spacer in the magnet first. Then I used the notch with solder filler on the shaft for the press fit again. Very easy and no fuss. The heavier #42 wire is easier to solder and work with too, not being so fragile.

      On my next test motor I want to try and eliminate the rear bearing and just use a long one at the front. I'm thinking that the rear one may not be needed with a gear drive setup, and mabe direct drive too with the closer fitting shaft. Also I'll go down to about a 20 ohm coil since there was no heat problem on this one.

brushless 2.5mm test motor no. 10