I am seeking advice on the functioning of ESCs and I wonder if anyone can help who either has electronic knowledge or has experience of using commercial ESCs such as the Electronize units which, as I understand things, use pulse rates that can be varied (In this case from 2000 down to 10 Hz). I would like to know if this pulse rate is selected by the user or does it adjust automatically? If automatic, what determines the pulse rate – is it motor speed? If manual, how do you decide what to use – trial and error?
My reason for asking is that I have never used a commercial ESC but have been making an ESC as part of the control of an electric motor that drives a feed-pump for the boiler for a steam engine. This project was inspired by the really excellent steam plant developed by Flashtwo - as described in his thread Flash-steam plant control:
http://www.modelboatmayhem.co.uk/forum/index.php?topic=15817.0The topic of the ESC has become a bit of a side track for me, but an interesting one (well at least I think it is
). I have designed and built a working ESC with variable pulse rates (from 15,600 Hz down to 61 Hz) but I'm curious to know how I can improve upon the design. I realise that commercial ESCs probably have subtleties built in that mine lacks - in addition to overload protection which I could incorporate if needed. From reading various sources (mainly concerned with larger motors than those used in small models), it seems the main feature of a good controller is to have a moderately high pulse frequency (about 20 KHz). There are a number of reasons for this e.g. the pulses should be higher than the frequency of the motors inner workings. Also my own tests with a MFA RE385 motor (which I'd be happy to detail in a later post) indicate a better motor performance as the pulse rate increases up to my max of 15.6 KHz. This is seen in terms of the lowest speed attained before stalling, lack of noise, linearity between pulse width and speed and the shapes of the electrical pulses as seen using an oscilloscope. However, at least one post to this forum has referred to low pulse rates being best for low speed and the description of the Electronize (and possibly other) commercial ESCs refer to pulse rates as low 100 and even down 10 per second as being an advantage.
In my tests, for each of several pulse rates I measured: 1. Motor speed versus pulse width, 2. The speed and pulse width below which the motor stalls, 3. The pulse profiles. Also noise was assessed. All these aspects seem to show that the highest pulse rate is best for both high and low motor speeds and for the best general controllability - at least for this particular motor and circumstances. So I am puzzled as to why commercial ESCs seem to use lower pulse frequencies.
I'd be happy to show the details of my ESC but I'm not sure that anyone would be interested as normally there is probably little sense in building an ESC when commercial units are easily available.
Thanks, Mike