Hi all, Bob's Boards, they were the cheap option and worked for me, there were other versions where a non-resistive pcb had low value resistors fitted, which acted as a stepped speed controller. Using the pcb idea glued to the top of a servo you could also attach micro switches that could be progessiively switched with an intermediate speed before full speed.
With the early electronic esc's they used ordinary power transistors a drop of 0.7 volt across the emitter to base junction, so you never got the full battery voltage across the motor. If the current to the motor was say 10 amps then there would be 7 Watts of power (heat) across the transistor. Hence the sometimes large heat sinks!
A partial solution to this was to put a relay with high current swiching ability in the emitter/base circuit so that when current got to maximum the relay would be activated and the contacts would short out the power transistor and deliver the full battery voltage direct to the motor.
When FET (Field Effect Transistors) took over the job there was just 0.1 volt drop so no need for the cumbersome heat sinc.
The forth-coming February edtion of Model Boats magazine should have a nostalgic look at early esc's. I am in frequent contact with the author of Flotsom and Jetsom and we discussed this, and as I had a few unopened Bob's Boards, plus some old Futaba 24 volt esc's which he wanted, I despatched them all to him as they were surplus to me.
I look forward to the article too.
regards
Roy
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