OS:CD Motor Circuitry
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CD Motor Circuitry
Circuitry for the CD Motor open source project.
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Circuitry
As prepared by Tim Harwood, March, 2006.
Developing circuitry for the CD motor
Functionality
- Pulse timing
- Pulse width variation
- Back emf-recovery
- Ability to handle 6-9 ohm coils
Heavy duty Reed switch Schottky Diode
Very popular due to its simplicity. You simply need to place the Reed switch by the rotor, and the passing pms will pull the contact across, closing the circuit. The diode is required in parallel to provide a recovery path for the back-emf, or the Reed switch will burn out very quickly. The mechancial contact also ensures decent back-emf output. Vary the distance of the Reed switch from the rotor to adjust pulse width.
Optical
Best overall brushless electronic timing system. However, generally requires more complex circuitry than other methods.
Hall ic
Halls provided fairly simple brushless electronic timing. However, they were found to be very sensitive to higher ohm stator sets. Therefore, they are not much use beyond 3-4 ohm rotor testing experiments.
Induction coil
You may need to give the rotor a push to start it.
Low draw
If the aim is to develop a fully self contained device that can run and re-charge a 12v lead acid battery, running the circuitry has to be part of the equation. Pickup coil commutation is the lowest draw form of timing.
Varying pulse width
Pulse width is best optimised with induction coils by varying the distance of the coil from the rotors, NOT the size of the coil.
Pulse switch input
In the given PNP induction coil circuit, the coil pulls a transistor, which in turn then pulls the main switch. The output from induction coils is so rough, that there is a large performance drop, if the main switch is directly powered from the induction coil. Pulse width can also be adjusted down once the motor is up to speed.
Optimal induction circuit
The given circuit has many best practise features:
- Can reduce pulse wdith when up to speed
- Main switch not pulled directly by coil output
- Diode to ensure current flow in desired direction
However, it would benefit from a MOSFET as the main switch. Transistors are more rugged, if lower performing parts, so the CD motor awaits the first decent Transistor-to-MOSFET pickup circuit.
External links
Egroup members always found the timing apparatus sold on this site extremely helpful.
See also
- CD Motor Open Source Project - main page
- Other open source projects
- PESWiki home page
