Failed Designs
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For the motor drive I have done experiments with two circuit configurations: single supply H-bridge and dual supply Half-bridge.


An interesting option shown above was using a control IC used in radio-control servos: NE544. It was possible to add simple H-bridge buffer to the IC motor drive output via opto-couplers, which also fulfilled my requirement for isolation.  Normally these IC's are driven by 1 - 2msec pulse width variation, but by giving it a fixed pulse via a timer, drive was also possible by inserting a voltage to the reference as shown. As output transistors I used 10A / 100V NPN and PNP types. Power was via two 12V 7Ah batteries.
The circuit worked reasonably well for driving the platform, but had one big drawback: The switching frequency was limited to about 120Hz max. The platform sounded like I was drilling in a concrete wall!