The MintakaFulcrum

Mk 2.0

Sept. 2002

Building Instructions, Photos, and Schematics

Here is a schematic for simple switching of the coils through a reed switch. C1 is optional but recommended.

• Switch Details
  
  
  • The switch used for this motor is a (huge) 200 watt rated mechanical reed switch that is timed by the main magnets in the rim of the rotor curtesy of Konehead... Thanks man... I love playing with these things!.

• Stator Construction Details
  
  
  • Primary coil wound with AWG 26. One stator at 13.4 ohms
  • Core is 1/8' thick by 2-3/4" long A36 mild steel rod.
  • The coil is wound to about 1" in diameter and to about 1 1/34" long.

• Rotor Construction Details
  
  
  • Two CD's were used as the rotor and the magnets were 1" diameter by 1/4" thick grade 8 ceramic magnets four stacked at each ninety degree quadrant of the rotor.
  • The magnets were hot glued in place with liberal amounts (about 3 sticks).
  • The shaft was a 5/8" stainless threaded rod. I made a collar that fit over the shaft and in-between the CD's with a lip on both ends so that they would have good center support. Each lip was the thickness of one CD.
  • The shaft was affixed to the rotor with two stainless nuts and a stainless washer on each side.
  • The shaft was machined to fit the bearings that I had lying around.
  • The mass of the rotor is ~ 450 grams
    
  • The bearings were from the pickup arms of a few identical old hard drives that I had come across. There were two bearings in each arm and I used 3 bearings on each end of the shaft. As you can see, they are very small and very low friction as I found out.
  • The rotor was then wound with filament tape... just in case. And as it turns out, this was not enough. :-)

• Rotor Update - CAUTION: Rotor Failure!
  
  

1. Rotor failure at 36 Volts (170 hz=2550 rpm) while still climbing in rpm... I would not suggest using more than 24 volts on this rotor design or a speed of over 2,000 rpm as the CD material is of very low tensile strength and will therefore be quite dangerous when it lets go under the enormous stress at higher rpm, even if your rotor is balanced perfectly.

Mk 2.0

Sept. 2002

Test Results, Discoveries & Conclusions

• Test Results
  
  
  • Coil resistance was 13.4 ohms.
  • Duty cycle ~ 45% timed off rotor magnets.
  • Could run on 12 Volts as well as 24 Volts. 36 Volts was too dangerous for the flimsy rotor. But man did it wind up like a mini tornado... cool!...but dangerous!
  • Measured power draw at 12.28 Volts at 140 ma for 1.67052 Watts electrical input @ ~1600 rpm
  • Measured power draw at 25.2 Volts at 200 ma for 5.04 Watts electrical input @ 2145 rpm.
  • Calculated max power draw at 12.28 V in Watts:=12.28 V times 12.28V/13.4 ohms times 45%=5.06W
  • Calculated max power draw at 25.2 V in Watts:=25.2 V times 25.2V/13.4 ohms times 45%=21.33W
  • It spins really good considering it's weight and imbalance perfections.
  • There was absolutely no torque (loading capability) at any rpm.

• Temperature Tests
  
  
  • Test #1
  • Temp before (ambient)=16 degrees (Celcius for us Canadians...eh?)
  • After 25 min at 12 V= ~17 - 18C
  • Right after shut off=~19C 10 min cool down=~19 C
    
  • Test #2
  • 5 min after 10 min cool down from previous shut off time.
  • Temp at start=~19 C
  • After 10 min at 12 V=~18C
  • Right before shut off 20 min run=~ 18 - 19C
  • 5 min cool down=~17 C
  • 3 min closed switch - stator full on=28C and still climbing but slowly.

• Discoveries
  
  
  • I am pulsing through a big reed switch where I can see the current generated during run down as well as while running by the beautiful violet plasma that forms during switch opening.
  • There was very low, (almost negligeable) torque.
  • It used very little energy.
  • Fairly high rpm
  • Very low magnetic coupling between non-powered stator and rotor magnets.
  • Switch will wear fast due to the corona caused by back induction currents.

• Conclusions
  
  
  • Switch plasma must be quenched in order to preserve switch.
  • Single small stator gave almost no torque. Will try increasing number of statorsin later experiments.
  • The 13.4 ohm rating for the coil seemed to be high enough to prevent my switch from frying and fusing shut. I think it is rated for 1 or 1.5 amps tops, so I might be pushing the upper limit of the switch.
  • The slightest mechanical resistance reduced rpm considerably.
  • Reed switch placement and therefore switch timing is critical to get good rpm.
  • Use a good big and accurate analog amp meter for measuring current draw.
  • A cap can be used in parallel as well to smooth out the pulses.
  • The temperature tests showed that the motor at 45% duty ran 2 to 3 degrees Celcius above ambient of 16. Motor ran "cool", but not "cold". I want to take measurements again with a lower duty cylce to compare.
  • Do not use CD's for rotors if you can help it. They can be dangerous as I had two rotors let go on me. See - new rotor

CAUTION: The information here is for educational purposes only. Any attempt at replication is done at full liability of the one replicating it. These motors can develop high rpm and high voltage depending on how they are designed. Build and operate at you own risk!

email me: motorlab@shaw.ca

For the copy-right/claim© 2001-3 by: Ian Coke-Richards and The MintakaFulcrum and may be freely distributed with due respect. Not for commercial purposes without permission and licence from the author. All commercial uses are subject to the terms of the user licence.