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Electronic retract reversal. Help please ?

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cagey02/09/2012 14:54:31
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I have an FMS P51d with a knackered retract unit, I also have a spare unit but it works in opposition to t'other so needs reversing. Anyone done this or know how to ? CML, advised it can't be done by just reversal of the motor leads, so I'm stuck. cheers fellas.

MikeS02/09/2012 15:34:20
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By retract unit do you mean retract servo. If so you need to reverse the +&-motor wires as well as the servo lead + & - wires. Of course this is only if it can be done on this unit.

Edited By MikeS on 02/09/2012 15:35:09

Bob Cotsford02/09/2012 17:25:06
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reversing lead?

Mark Powell 202/09/2012 17:47:23
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MikeS,

Reversing the plus and minus on a servo lead will simply result in its destruction. Possibly the receiver and battery as well. Thats's why the servo plus is in the middle, so you cant accidentally do it.

Chris Bott - Moderator02/09/2012 18:40:27
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If it's a self contained electric retract, cagey, as the thread title indicates, then a reversing lead as Bob mentions is probably the best option.

The only other choice I see is running it off a separate receiver channel slaved from retracts but reversed.

It seems odd to me though that you can get a spare that is the wong way round.

cagey03/09/2012 12:36:35
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Thanks fellas. Yes it's an electromic unit, identical to the E Fllite 10-15 type which came out after it. Researching other sites tells me servo reversing leads doesn't work with them, neither does swapping motor connections. This is just plain daft to me and I'm surprised no one else hasn't had a similar problem and knows of the answer. They're only £14 a pop, but unobtainable for the moment, that's why I'd like tp reverse one- simples. Ah well, back to the head banging.

MikeS03/09/2012 15:24:16
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Mark. I stand corrected. you of course are correct.blush

That will teach me to go from memory when I have not do it in a long time.

Edited By MikeS on 03/09/2012 15:25:26

Peter Beeney04/09/2012 21:21:07
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Cagey, - Is it possible to easily get inside these retract units? I very much suspect probably not, so in which case it might not be that easy to reverse the travel. I’ve not been seen these in action, but I assume this is a small brushed motor, similar to a servo motor, turning an Archimedes’ screw. It would wind the mechanism up to one end and then stop using a (travel) limit switch. Changing the tx switch reverses the polarity on the motor, then the motor unwinds the mechanism to the other end and again stops using a limit switch. So, if it were possible to change just the motor connections, and that’s a very big if, particularly if the motor is soldered to a PCB, then you would reverse the operation of the mechanism, and thus the retract unit. There is absolutely no doubt that changing the direction of current flow within a brushed permanent magnet motor changes the direction of rotation. The evidence of this can be seen in any servo operation.

I really don’t know if this is any help at all, this is all supposition on my part regarding the operation. But it may well at least be worth taking a look to see if you can get into it, are there any screws holding the case together, or is it glued or fixed in some other way so you cannot take it apart? In the old days you could dismantle servos and reverse the direction fairly easily, but nowadays, in some cases anyway, although you can take the bottom plate off, to get at the internals almost requires breaking it apart; and even then it would almost be a full blown engineering job to change the connections around.

As Chris says, using as separate channel in the receiver would be a very simple and suitable option, if you were using MPX you would have been able to do this years ago, but now I believe that more and more transmitters are getting a bit better at doing these kind of tricks. I’ve always felt it’s just one of the many advantages of owning a fairly sophisticated computer transmitter.

Good Luck.

PB

Chris Bott - Moderator04/09/2012 21:48:04
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I'd try onther Rx channel and a mix if you can cagey, I'm sure someone here can help with the programming if your Tx is capable and your Rx has a spare channel.

I can't understand why a servo reverser wouldn't work though for the life of me.

cagey04/09/2012 23:20:05
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Again, many thanks for all the suggestions fellers. Special ta very much to Pete who has been nearest to my own thoughts, if only it were that simple Pete. The units are very easily stripped and the connections to the motor easily swapped at the motor end, not so at the PCB which has the joints liberally coated in white sealant, but do-able though. That was originally suggested to me by CML, the distributor who supplied the back to front unit, this was advised to them from FMS themselves, who later said that was incorrect ( too late) as it would wreck the thing (it did !) Now metinks disam poo, because they are as you rightly say a simple little brushed motor driving a screw jack via a gear train moving a cam along each way to an end of travel mini micro switch. The polarity of which dictates direction of travel, so lead reversal should equate to direction reversal etc. I can only think that the overtravel tolerance is finitely minute and needs setting up with more complex equipment than the average DIYer is capable of owning-( piece of electric string and a light bulb maybe ? ) Well £14 ain't going to break the bank, but still I'd be chuffed to be able to beat the bugger into submission though. Ho Hum !

The word from some guys on RCG Chris is that they've tried a servo reversal lead and the electronic clever part of the unit didn't get it and drove to overtravel which knocked the mini micro off the PCB, breaking it's push button in the process. So not recommended by them or another couple of guyswho said they just don't work at all, make no difference. I'm very sceptical about that and that's why the OP, in the hope someone has actually done this with one of these bits of chinese poopy things. It's a lark innit eh ?

Cheers all, cagey.

cagey04/09/2012 23:25:22
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PS to above, don't got any more spare channels what with flaps and LiFe flight pack all 7 are busy and I'm too mean to lash out on an AR8000 (again)

Why can't we edit our posts people, or can we ? Night night.

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