Quote:
Originally Posted by vintagecollect
CAN someone please PM me on any available wheel motor control circuits ss recently done.
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I've had to build a different motor servo for each of my five breadboard wheel sets because it is seemingly impossible to build one single circuit that works well for all of them.
This is because each set has a different mechanical configuration, a different motor, and a different size color wheel. All of the mechanical and wind resistance differences translate into very different control characteristics for a servo system to deal with.
I'm using 1750 RPM split-phase capacitor run induction motors of from 1/20 to 1/5 horsepower depending on wheel diameter. The common thread that connects them all is the use of the same type of speed control and adjustment: AC from the 120 volt line drives the control circuit and thus the motor. The control circuit is fairly simple and brute force:
To set the correct range of motor speed a 25 to 50 ohm, 25 watt rheostat is wired in series with the AC source, the motor and the other control element, a saturable reactor transformer arrangement made of two identical 35 volt, 2 amp filament transformers. The 35 volt secondaries are wired in parallel, and the primaries are wired in series but out of phase.
When a DC control voltage from the servo amplifier of from 10 to 40 volts is impressed across the primaries, the transformers saturate and pass the full value of AC voltage on to the wheel motor.
Two position and phase sensor pickups on the wheel provide synchronizing pulses back to the servo amplifier which are internally compared to the red field ID pulse or other synchronizing signal coming from the video source to spin the wheel at the correct speed and phase to display the right colors.
None of the servos I built from scratch ever worked the first time. Each one took lots of testing, measuring voltages, studying waveforms on the 'scope
and sort of working into the 'sweet spot' of the design so the wheel would lock up every time I turned the set on. The CBS wheel servo took several months to make reliable, and I continued for much longer fine tuning it.
Each set I built is a test bed and a bread board, not a finished product and not a complete and tested design that could be turned into a kit of parts like the original Colordaptor.
There are other means of spinning a color wheel.
At least two other VK members who have built mechanical sets have used DC motors and servos built with phase locked loop chips.
Some have used triacs to control motor speed, but I found early on although very convenient, they chop the AC voltage which causes motors to over heat rather quickly.
So far as I know, there is not a motor control device 'kit' available.
As each set I built is different, I built a different servo for each one, no two being alike.
Anyone who builds a color wheel set from scratch will have to build a wheel servo that is unique to his set.
I got ideas for the servos I built by reading VTR repair manuals of the 70s & 80s and studying the circuitry of the Col-R-Tel , Colordaptor and the Jay Stanley Projection wheel set articles in the electronics magazines of the 1950s. These articles
are available online and I will send links or the actual articles to anyone interested.
Please Note: Lots of assembly is required. Lots of effort and lots of frustration
will occur before your wheel will sync up every time.
There are no guarantees, and no warranties. You will become an inventor.
It is one thing to build a circuit to lock the local color oscillator in a TV to the signal from a DVD player, but quite another to precisely balance a 4 lb. plastic color wheel and develop a control circuit to keep it spinning at 599.4 RPM and within about one degree of error per rotation.
Best Luck and remember your mileage will vary.
Cliff