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[nsa66]

As part of my TID tug's refurbishment I am planning to use the output of the ESC to control a second, much smaller, geared motor which would be used to create a pulsating effect in the smoke unit. Additional circuitry will be necessary to allow this to turn at a fixed, low speed at idle as well as to increase the pulsation speed as the main motor revs increase.

As I understand it the ESC produces a series of pulses, the length of which increases in proportion to the throttle setting. Is the voltage of these individual pulses the same as the input voltage to the unit (i.e. propulsion battery voltage, which in this case will be 12v)?  Is there any way of easily converting this series of pulses into a proportional (at least approximate) voltage, i.e. half throttle equals 6v etc? If this can be done I can use a relay to switch the feed to the smoke pulser between a fixed "idle" supply and a proportional supply when the boat propulsion motor starts to run.

Maybe some of you electronics gurus out there could point me in the right direction.  As ever, all advice would be gratefully received.

[dreadnought72]

I think this is correct:

The power pulses emitted by the ESC are at the full-bore input voltage.

Half throttle - where the ESC is running on 12V - means pulses are 50% 12V and 50% 0V.

...Which is effectively 6V.

Does this not mean that the ESC is already doing what you require, without the need for a relay?

Andy

[malcolmfrary]

Attached a sketch of a bit of circuit to do the job.  Since Maplin have decided to hide the useful stuff, even if they still sell it, I looked elsewhere found the parts in ESR's on line catalogue ( http://www.esr.co.uk/ ).
It consists of a device to watch the output from the ESC (the opto coupler), which them mimics the pulses to the output transistor.  This drives what I have called the fan motor.  The resistor paralleling the transistor provides a bleed current to let that motor turn at you preferred minimum speed.
Pules from the ESC switch one of the diodes on and off.  The light from that diode switches its corresponding opto transistor on and off.  Forward does one pair, reverse does the other.  Either pulses the output transistor, which drives the motor faster or slower, but always in the same direction.
Using an opto isolator saves a lot of thinking in the design department, the Darlington transistor was chosen because a/ I am used to it, b/ its fairly bullet proof  c/ it needs very little drive current  d/ fairly cheap.  The idle bleed resistor value depends on the motor and supply voltage, but a ceramic type of fairly high wattage would be the best type.  Almost any variable type would just add to the smoke before dying.  With that resistor, there should be no need for a protection diode, but the motor should have normal suppression fitted.

[nsa66]

Thanks Malcolm, that is brilliant. If it doesn't do the job exactly as shown, I'm sure I can tinker with it a bit. Incredibly useful website too - especially since Maplin turned into yet another Chinese gadget shop.

[malcolmfrary]

Thanks Malcolm, that is brilliant. If it doesn't do the job exactly as shown, I'm sure I can tinker with it a bit. Incredibly useful website too - especially since Maplin turned into yet another Chinese gadget shop.

I thought that Toys R Us was their aim, but............

The circuit should work OK, I used to use the elements to make a higher power ESC from a servo board, until the price and size of ready made ESCs came down, and the performance went up to somewhere beyond belief.