Cdrom motors
Here we go; these fascinating compact brushless motors are a hobbyists' and tinkerers' delight. The base structure is the platter motor from a dismantled computer cd-rom drive. Easily and cheaply available, dead or old drives can be begged from computer shops or friends, I even bought one once! At the time of writing I have one working reliably in my Moth microheli. It is powerful and weighs only 24grams. You will need a brushless, sensorless motor controller to drive one, I've used an old Jeti06, Castle Creations Phoenix 10, and a Tsunami 10 successfully.
Below is a guide to dismembering and modifying the motors. Note it is just my approach here, there are many and more elegant ways to skin this cat, I have a bench vice and hand tools but no lathe.
Here is what you see with the case dismantled (40X Samsung shown):
The motor must be removed, the three screws you see are very small, 0 Philips size screws on this one. Here is what the motor then looks like:
Note there are other useful looking parts, I've ended up with loads of screws, gears and bits. In particular, check the motor shaft size, it is often the same size as the slider shaft for the optical system, 3mm, which can be used to make a longer motor shaft if required. (Thanks to Reuben for reminding me of this :o) )
We certainly don't need the heavy flywheel (shape and structure varies) and on this one the shaft was knocked through using a piece of steel rod. This is also used to knock the cap off the other end of the motor:
The little washer is the plastic circlip, easily removed, which holds the shaft in place. Next I saw the mount plate down, retaining two of the original holes (one is a bit oval) and break out the circuit board, making sure I don't damage the stator core. Note the motor being sawn is a different one, but very similar style. Since I like to replace the shaft bushes with ballraces, a metal drift is used to knock the originals out. A small file and careful drilling enlarges the two mounting holes to take a tap, 6BA in my case, similar to 4-40 and M2.5 screw size.
Windings were tackled next. My motors are all "star" wound so far, it gives a slower motor than "delta" winding. I have used 0.4mm (26guage), 0.5mm and 0.3mm wire so far. 3 lengths of wire are wound on to the stator, all joined together like a letter "Y". The free ends of the wires all go to the speed controller. Starting on one stator tooth at random, wind your turns on as neatly as possible. Skip the next two teeth, wind another one, coiling the wire the same way around the core as your first one. Skip two and wind the last tooth in the set. Don't scratch the enamel off the wire, short circuits will spoil the motor's running. The stator then looks like below.
If you click the picture it will take you to some more winding pictures. NOTE LARGER PICTURE FILES may take a while to load on a modem connection.
Repeat the above twice more and the windings are done! Takes me an hour or two to wind a stator. Note I have routed the wire "over and under" one of the teeth to save space on top of the stator, there is little headroom under this bell. It doesn't seem to affect the motor's running. Solder three of the ends together, say all the winding "finish" ends, and your chosen connectors for the speed controller to the other 3 ends, say the "start" ends. Don't mix the start and finish ends!
Note though it is Ok to use the original shaft, this is commonly 3mm, easier to get bearings fitted if your motor centre will take say a 7mm bearing. I used a 2mm carbon shaft on this particular motor, as 2mm pinions and bearings were what I had. The ballraces had an outer diameter of 6mm. The complication was to centre and mount a 2mm shaft in a 3mm hole. Well I got creative with bits of tube and alloy glued in place with slow epoxy, and used the stator and bearings to centre the shaft. Amazing what you can do with layers of thin sticky tape too.
With bearings and shaft secured, the motor only needs a controller and it should be ready to run! Check nothing catches or rubs, mount the motor securely, use your preferred motor connectors. I like 2mm gold plate round connectors as on my batteries. Health warning! : these little motors can run up to quite alarming speeds offload, watch your eyes as with any rapidly rotating object. I ran one up once dangling it by the wires, and got it going a little too fast. The unsupported shaft "whirled" slightly then BAM! The whole motor disappeared, grazing my thumb, tearing the wires off. I turned, shocked, to retrieve the bits, as the rotor wound down behind some rubbish in The Shed. The magnet ring and stator were damaged, though since the motor has been rebuilt.
As you may have seen on the Moth helicopter page, my first attempts to fly these motors wasn't a shining success. The old Jeti 06 controller started and ran them well, but its coarse throttle control wasn't ideal for heli flying, probably Ok on a fixed wing model. Not wishing to use my Schulze controller as I had heard they were not happy on cdrom motors, I tried again using the Castle Creations Pheonix10 controller. Alas at first it didn't run well, losing sync with the motor as soon as a load was presented. The solution I have now is a combination of later firmware in the controller (thanks Patrick :o) ) and stronger magnets in the motor. The magnets I have used are N45 square magnets size 5x5x1mm, available quite cheaply from Supermagnete in Switzerland, and other suppliers I have seen on the web. I bought 150 at about 11p each including post and currency costs. Link to Matthias' site from the list on the Piccolo page. Note at this time the magnets have been superceded, check for current spec.
The old magnets have been chiseled out, supporting the bell on the vice top to prevent distortion. Note! They can be removed more gently by soaking the bell in acetone (I haven't tried this at the time of writing) or by heating, I use a small propane/butane gas torch and heat until I get a smoke and flame output from the magnet, which usually shakes out by tapping the shaft on the vice top. I hold the shaft with forceps to handle this.
12 new magnets glued in with slow setting epoxy, making sure that alternating north and south poles face inwards. This can be fiddly, sticky and annoying as the magnets insist on sliding about. I have a pair of stainless tweezers which don't stick magnetically to the magnets! I also had to drop a plastic disc in the bottom of 2 motors as the magnets would have gone too far down and not lined up with the stator.
Tip: take your stick of magnets and mark one end with indelible pen. I use a "+". Remove the magnet and mark the next one down, it will be the same pole as the first. Mark 6 this way. NOW TURN THE STICK AROUND and mark the opposite end. Here I use a "-" and you can mark 6 like this. Now you have 6 magnets with the North poles marked and 6 with the South poles marked, so you don't mix them up and put 2 like poles together in the bell. Click the picture below to see the marks.
At time of writing this page I had flown 5 motors:
Motor 1: 15 turns 0.4mm wire, neodym. magnets, 28.6mm diameter, height 12.3mm from mounting face, 3mm shaft. Stator 24.4 x 3.6mm. Pressed steel mounting system. Weight 23.3g. This is the first cdrom motor I took apart and I think is from a no-name 32X cd drive. Gearing is 10/96 using ECO8 motor pinion, end trimmed down slightly. Lively flights of about 20 minutes so far on 3 x 1200 Li-poly pack. (Update: flights without the Christmas decorations aboard now up to 24-25 minutes. Power is more than adequate.) This is staying in the Moth for a while! Pictures below:
Motor 2: 19 turns 0.4mm wire, neodym magnets, 28.3 x 10.5mm + the shaft support on top. 2mm shaft, brass core and steel plate mounting. This is the Samsung 40X in most of the photos above. Too cool a winding or too low geared at 10/96, it needs almost full throttle to fly on 8 x 750NiMH cells, in my oldest Piccolo, using stock blades at the moment for trials. Runs nice though, and got 13mins 40 on the last flight, a couple of minutes of that would be in ground effect. You can see in the installed picture, the mod required to the front undercarriage mount with this size motor. Rewound to 14 turns to pick up the revs a bit.
Motor 3: Stock windings! Original magnet ring, 25.1mm diameter inc. the rim x 13mm mounting face to front of bell. 2mm steel shaft (original), brass core and alloy plate mounting (home made). Creative DVD drive. Weight 23.9g including the prop adaptor. The GWS IPS power unit you see weighs 29.6g. Flown successfully in the Picostick, Kevin Davidson caught it in flight at Harrogate where it circulated gently for about 1/4 hour on 8 x 750 NiMH before I landed to check all was still Ok. Power was low on the 7 inch rubber motor style prop and with the heavy battery it needed a handlaunch. The grey 6x4 prop was way too small, would barely taxi. Will try a bigger prop next.
Update: Now modified with magnets, bearings, and 24 turns of 0.315 wire, takeoffs and performance on 3 lithiums are superior to stock setup, 9 x 4.7 GWS prop.
Without further
modification, the motor has now successfully flown my new Shockflyer. The light
weight means an all-up weight of only 182grams (6.4 oz.) with 3 x 340cells and a
GWS 9 x 4.7 prop. Checks with a meter in circuit show a current of about 5 amps
full throttle, and it can prop-hang on 60% throttle.
Motor 4: Wow! 14 or 15 turns (I think!) 0.5mm wire, 28.2 x 9.8mm, Neodym magnets. Unbranded 48X. This is in fact the motor shown above in the sticky tape pictures, and also wedged cruelly in the vice jaws. It is also the one which took off spectacularly from the bench in the accident report. The motor can isn't quite straight and has a visible wobble. Replacing the 40X (2 above) in the Piccolo, 10/96 gearing again EXCELLENT performance, hovers at 60% throttle power to spare for climbout and good duration. 8 x 750 NiMH, 11mins50 out of ground effect after using the battery to try a different motor, fiddling with the controller settings and running this motor up on the bench as well. Further flights with old 250 packs confirm that flight times are improved, 3mins 50 and 5 minutes are slightly better than the Astro's times. This one's a "keeper" as they say, will do more testing as I can. Power also seems equivalent to my excellent Astro 01. Has a nasal turboshaft like sound much like the 40X.
Motor 5: Tiny! 15 turns 0.315mm wire, 23.6 x 12mm, neodym magnets. 3mm shaft and pressed steel mount, one 3x7x3 bearing is stuck straight into the stator, the other into the base plate. Artec 50X drive. Weight 16.8g! Unfortunately I distorted the can slightly removing the magnet ring, and found a magnet rubbed on the stator afterwards. After relieving the outside of the stator slightly where it contacted, and running the motor a while I appear to have a running clearance, but the motor heated up quickly installed in the heli. I found the pinion was catching on the battery, but suspect the real cause is still magnet-stator clearance under load. Power is similar to flying the original 295 motor, and despite the wasted heat, cumulative time over 3 flights was 14 minutes with 8 x 750 NiMH.
Further info on this motor: I chipped out the magnet which had been rubbing on the stator, and also cleaned up the outside of the stator with wet/dry paper. As a result, I seem to have clearance, running offload for several minutes at full throttle produced no excess heat - excellent! Flights of 13.5 minutes have now been achieved, power feels similar to the stock 295 motor, adequate but the climb is slow. The motor gets hot to the fingertips but I can keep my fingertip comfortably on the can. The heli has lost considerable weight at the moment, with this motor the weight of my (Bell tailboom) original old Piccolo is 156.9 grams without battery. :o)
http://groups.yahoo.com/group/lrk-torquemax/
: homebuilt motors interest group with an active mailing list and useful
links, info. To see all the files you will have to register with the
group.
http://www.rcgroups.com/forums/index.php?topic=ezone
: The E-Zone forums, frequent threads in the power system and indoor subjects
http://members.jcom.home.ne.jp/4223215501/index.htm
: Satoru Sataki's enthusiastic pages about small electrics with cdrom based
motors.
For suppliers of parts used in the above motors, see my suppliers list on the Piccolo page.
More as I find them!