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Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I just picked up a D.C. brush type motor that looks like it just might do the trick for a stable and smooth spark gap. I had a lot of trouble getting the count 'correct' from the rotary optical counter because I had to keep adjusting the Systron for the proper amount of attenuation. I was getting counts in the 23k and 24k range, and figured this must be the result of mis-triggering on the input. So I kept at it, kept adjusting the attenuation, and then the result became a consistant 10k count. The motor works very well and is very smooth. Unfortunately I have no specs for this motor, but no worries, I am really good at determining these things.
The motor works quite well at 50V, and is at about 12XX r.p.m. which leads me to believe that this is a 90VDC motor and will run reliably at or slightly above 1800 r.p.m.
So what makes this a project? well, I will add the 90VDC controller in the future if I'm good enough to get that working reliably. I envision a regulated voltage source at around 90V with its own feedback of the optical counter locking it in at 1800 r.p.m., and then life would be really good.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Well it turns out that the rotary optical counts 1000/ revolution. So I recalculated that I need 30 K counts/second, which then gives me 1800 r.p.m.
Now I was going to solve the problem myself with a closed loop control, and I will in the future, but since there is a time limit and a need for a proper solution, I must cheat.
I have here a DC motor control that gives me my speed I need and then-some. I have to enable an optoisolator to activate the controller. I want to enable the slow speed that is preset, then enable a higher speed to run. Why? Well because I want to make sure that its clearing okay for a while before ramping up to the final speed.
I also wanted the controller to send an enable pulse when the motor has reached the final speed, but we'll do that with a delay relay in the control board of the Tesla coil.
This is a superb control by Dart, and a great motor too. Very smooth and stable. It's giving me better then 1% without load.
Next step...turn this badboy into the rotary spark gap with precision control. A good coil is coming!
*********Update**********
I now have the motor tachometer sorted out for the most part. I need to make it all 4000 series logic so that its more flexible under the stresses of the EM field.
The motor outputs 30kc, so I needed a standard frequency of 66.66Hz for the display to readout 1800 r.p.m., so I took a 2MHz crystal and divided it by 30k. It works nicely and I hope to have a good looking tach. in a short time.
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