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ESC master and slave
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 Posted: 1 June 2016 10:22 am
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Mike Smith
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Appealing to the electric flight boffins out there.
I am informed that when using two ESC on a twin model you can use one ESC as a master to control a slave unit so that the motors run at the same speed. Is this so? And if so how does one achieve this bit of electrickery.
Must have motors "synced" for next project.
Mike

Last edited on 1 June 2016 10:23 am by Mike Smith



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 Posted: 1 June 2016 07:01 pm
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martinw



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I haven't heard of that one Mike which doesn't mean it's not a fact.
Have you considered using two KP timer units. The speeds could be synchronised on the pots as could the running time and decay time. There could be a difference in the arming time but any discrepancy could be over come by adjusting the run time to finish at the same point. If there were a big difference it would mean not releasing the plane until both props were spinning. Another plus is that the thrust from each prop maybe slightly different and this could be compensated for by speed adjustments
On the Lancaster I had identical motors and ESC's which ran within a couple of hundred RPM but any discrepancy could be compensated with flight controls which you don't have the luxury of on freeflight.
It would need some setting up but could work.
 
ps what is the next project

Last edited on 1 June 2016 07:03 pm by martinw

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 Posted: 2 June 2016 08:28 am
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Phil F
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Hi Mike . I'm Not an expert on electric power but thought that if two ESC were used they were both connected to Rx via a "Y" lead.



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 Posted: 2 June 2016 10:00 am
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Mike Smith
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Martin and Phil
Just in case this is for a free flight scale model.
The setup I am using has the usual lipo battery, 2 esc, 2 motors. the esc are pluged into the flight profiler (inplace of an rx) it has 2 sockets so a y lead is not needed.
The rpm are not too far out, a couple of hundred, but needed to know if they can be "synced"  through the flight pattern without getting too complicated.
It would seem that I will have to trim to the variable thrusts as I have in the past unless we can "find aman that can".
Next project is still brewing but will have to get a move on as I destroyed the Twin Pin at the Nats. It just refused to fly in a safe pattern. Too little wing too much weight too bigger fin / rudder areas. Therefore the very slight mismatch on rpm was amplified and could not be overcome by any adjustment that I tried. Oh Gosh.
Mike



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 Posted: 2 June 2016 05:17 pm
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martinw



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Unless you are extremely lucky, getting two identical motors, esc's and props is not likely.
The controller with duplex connectors will give an identical signal but from that point you are in the hands of a mass produced and cheap set of components, plus electrickery subject to current variations due to slight resistance in connectors, lengths of cables etc. These differences may be negligible individually but collectively you can get the result you had at the nats.
I think that using two controllers you could tune out the variables. Not easy but possible.
Martin

Last edited on 2 June 2016 05:18 pm by martinw

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 Posted: 3 June 2016 11:08 am
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Mike Smith
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I have been in touch with Derek Knight, who makes the timers, and he gave me some very usfull info.
From this I will set up a test rig exactly as it would be on the model and test and change items until best possible match is reached and trim the model from there.
It may be the switch from 2 to 3 cell lipos did not help.
It is possible that I used wiring that was underrated for the purpose and created resistance and so variations that added to the problems. Learning!!!

Mike



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 Posted: 3 June 2016 03:40 pm
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martinw



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Going from a 2S to 3S lipo would increase any difference because the motor speed is directly related to the voltage (kV). For instance the change of lipo gives a 50% greater voltage which equates to 50% increase in any difference in rpm  between the motors.
Keep the cables the same length and type both in and out of the esc's and as short as practical.
The KP module will get it's power from one of the esc's which will reduce the current available to that esc. On the Lanc I disabled the bec function on all esc's and powered the rx and servos with another battery. This is a bit different to your free flight application as the draw is much higher but the principles the same.

 
Martin

Last edited on 3 June 2016 03:41 pm by martinw

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 Posted: 6 June 2016 09:02 am
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Phil F
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Getting matched motors must be a nightmare ! yes i can understand that as i have tried rewinding a few . When re winding you find that the phone rings non stop :shock:your wife calls to say a cuppa is waiting :D, When you don't answer she calls again >:oso count is lost , the postman calls and needs a signature >:o>:o.  It goes something like 221, 222, 223 224,, phone rings  long discussion  errrrr! unwind .fresh wire and one ,two  etc . Even when one turnout it can throw a motor . When winding ALLWAYS have a pen and paper handy to record turns and direction etc .



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 Posted: 6 June 2016 07:34 pm
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Bill

 

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I still prefer pictures better than writing, easier to understand.:shock:

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