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CDROM "Flight engine"

hier geht's zur deutschen Version

While reading some articels in magazines about brushless motors and following the discussion in the newsgroups, I decided to try the conversion of a simple CDROM-drive into a high-performance flight motor. After some experiments and with the friendly help of enthusiasts in the LRK Newsgroup of Yahoo I was able to sucessfully build a very cheap, light (21g = 0.74 oz) outrunner motor, which is able to replace a Speed 400.

Thanks to the short life period of todays Personal Computers there is enough raw material. The only problems is to find CDROM-drives which match our needs. The drives should by easy to disassemble and it should be easy to remove the useless parts without damaging the motor.

After several unsuccessfull attempts I found a NEC CDROM-drive in an old Dell Desktop PC, which was easy to open and - most important - the motor was easy to disassemble without using tools or brute force.

The original CDROM motor

The mechanical structure of CDROM drives can be very different. Some CDROM drives are well suited for our needs, some are not. The axle should by long and thick enough to attach the prop and a it is also very important to find a good way to install the motor in the aircraft. The magnetic ring of all motors I have seen, are too weak to get the power we need. Most brushless controllers will fail at higher RPMs and/or under load - the motor stops with a awfull whining sound.

Dimensions and data of the modified motor
Diameter of the bell: 28.5 mm / 1.122 in
Height of: 7.8 mm / 0.307 in
Diameter of the axle: 3 mm / 0.118 in
Lenght of the axle: 6.8 mm / 0.267 in
Diameter of the stator: 24 mm / 0.944 in
Height of the stator: 5.2 mm / 0.204 in

9 poles / 12 5x5x1 magnets
20 windings
0.5 mm wire
delta

6x3 Graupner CamFolding Prop

7x350 AAC Sanyo
N45: 12080 RPM - 7.10 A
N48: 12700 RPM - 7.15 A

7x500 AR Sanyo
N48: 13400 RPM - 8.5 A

Preparatory work

The rotating bell (flux ring) can be pulled out gently. The inner side of the bell is coated with a flexible, magnetized plastic ring.

The stator and the mounting plate are screwed together with two small screws. After unscrewing the statorit can be removed from the mounting plate an the bearing pushed off. Now the thin wire must be removed from the strator completly.Be careful not to damage the surface of the stator !

The magnetized plastic ring must then be removed with a sharp knife. Watch your fingers! You will need them later.

Modification of mounting screws

Remeber the old, noisy Cox engines. I decided to use two 2x16 mm screws replacing the original ones.

These screws must be flattend on 3 sides to fit perfectly into the stator. By using this method the engine is easy to disassemble and can be mounted in a stable, comfortable way. The screws also conduct the heat from the stator to the heatpipe.

Use a little file to flatten the screws. The screws will also improve the heat transfer.

Rewindung

Rewind the strator using high quality 0.4mm - 0.5mm (0.015 in - 0.02 in) copper wire. 17 - 20 windings per teeth is a good choice.

The fewer the windings the more RPMs. More windings will result in a higher torque. Try to place the wires in paralell and try to avoid potential distractions like TV, mobile phones or children during your work. The insulation of the wire must remain undamaged - this is mission critical!

You can choose between "star" and "delta" winding. With "star-winding" the motor will have a higher torque, less RPMs and will pull less current (amps). "Delta" will result in a "hotter" engine with higher RPMs and more power, but will pull more amps and will produce more heat. The star is also more difficult to handle for the brushless controller.

Quality check

Check the quality of the windings with a multimeter or with a battery and a lightbulb. The wire MUST not be broken and windings MUST be insolated from each other and from the strator. If one of the tests fail, remove the winding and try it again :-(

Cabling

Remove the insolation of the 6 wires with a sharp knife. Solder the ends of the wires in star of delta configuartion forming 3 connections. Use heat-shring tubing to insolate the wires and solder 3 high quality plugs at the end of the wires. Take a look at the pictures, they say more than a thousand words. Alle wires must be properly insulated to avoid a short circuit.

New magnets

The stronger the better. I am using gold-plated NdFeB magnets, size: 5x5x1 mm (0.196 x 0.196 x 0.039 in). (distributor in Switzerland: www.supermagnete.ch, mentioned in the newsgroups: www.engconcepts.net . To find distributors in other countries use Google or post your question to a newsgroup.

VERY IMPORTANT the magnets must be mounted N-S-N-S..., otherwise your engine will not work. A good way to check the polarity is to place 12 magnets on a table side by side, lay a piece of transparent glass or plastic on the magnets. Now test with another magnet the polarity.

Now you can take one magnet after the other and glue it into to bell. Use a high-quality epoxy glue (Araldit or Uhu Endfest) - do not use 5-minutes epoxy. The distance between the magnets should be the same. It takes some care and time to do this job.

After the glue is hardened, you should fill the gaps between the magnets with a mixture of microballlons and epoxy. Be careful no to use too much.

Assembly

Place the screws through the strator. Then the bearing over the screws into the stator then fix the assembly together with a nut on each screw. Fit the axle of the bellhousing carefully into the bearing. Make sure that the wires do not touch the surface of the bellhousing by placing a plastic spacer (washers) on the axle (if necessay).

Now you can connect the engine with the controller.

In order to be able to mount the propeller on the axle you have to probably widen the hole of the prop. When equipped with strong magnets your motor will be able to drive a 7" prop. Sometimes it is necessary to do some experimenting to get maximum performance.

The magnetic forces are strong enough to hold the bellhousing and the prop together. It is not necessary to use a ball bearing - the original bronze bearing does a good job. It is also important that the heat transfers smoothly from the strator to the heatpipe.

First test

You should start the motor for the first time without the prop. Listen for friction points. If the motor runs smoothly you can try the first run with the prop attached. You can change the direction of rotation by exchanging 2 of the 3 connections between the motor and the controller. Beware of the rotating blades!

Aircrafts

Java 150 von Simprop/Scorpio

The airplane shown above is a "Java 150" from Scorpio/Simprop with 59 inch wingspan.
The plane was powered with a geared Speed 400 (4:1) using a 7x1100 mAh NiCd pack. This system was replaced by the CDROM-engine and a 7x350mAh NiCd pack. The climbing rate is good and the gliding performance is much better because auf the reduced weight.

Calimero von AFF

The CDROM motor fits very well into the Calimero. Calimero is a small (39 inch wingspan) electric glider built by AFF (Germany) which has outstanding flight performance. The plane is originally designed for a speed 300.

Flight experience
The calimero was originally designed as for slope soaring and has amazing flight speeds.

Performance enhancements
After much thougth and a series of tips from other people I redid the motor windings (20 windings delta, 0.5mm wire) and replaced the 7x4.5 with a 6x3 prop. Now the motor pulls 6.5A. It fits perfectly to this type of plane. The airplane is now able to climb at an angle of 30 to 45 degree.

20 windings
0.5 mm Cu wire
12 Magnete 5x5x1.2 N50
Delta
Airgapca. 0.4mm
6x3 Graupner CamFolding Prop
7x500mAH NiCD or 7x1100mAh NiMH
6.5 Ampere full throttle
13'400 U/min

With 7x500mAH (this battery fits perfectly - no need for additional lead) the motor runs for about 5 minutes.

Remark: Stronger magnets always resulted in better performance (more thrust, less power).

The CDROM motor also fits well into the famous "Shockflyer". You should use a bigger prop and "Y" wiring. The weight: thrust ratio is about 1:1. Vertical acceleration and "torque" is not possible with this configuration because of the weight of the NiCd packs. Using Lithium Polymer cells would bring a big change ;-)

Conclusion
With this type of motor I experienced the best results. You can actually fly all the time without waiting for recharging the batteries or cooling down the motor !

Links

 

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© 2014 Lucky Luke Records Inc. | Imprint | Disclaimer | 20 July 2006
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