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Electro mechanical retracts control board

Looking for a circuit diagram or a control board.

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jimmac06/08/2020 22:47:04
72 forum posts
5 photos

I am looking for a control board or wiring diagram to operate a set of retracts fitted to a DB sport and scale Hurricane. The retracts operate on a screw jack system with limit switches for up and down. I think SM services may have done something like this for the LMA guy's. Any help is really appreciated.

Attilio Rausse07/08/2020 08:30:55
118 forum posts

If your retracts have a standard 3 wire servo lead then you just connect them to a spare receiver channel, if there are only two wires then you will need a separate controller (around £10) on ebay.

jimmac07/08/2020 10:28:01
72 forum posts
5 photos

Hi the control cables have 3 and 4 cables. I will add pictures today.

jimmac07/08/2020 13:55:09
72 forum posts
5 photos

20200806_203019.jpg20200806_203010.jpg20200806_202955.jpg20200806_202947.jpg

Attilio Rausse07/08/2020 15:54:36
118 forum posts

Looks like a very early version, now if it was me I would try the retract with 3 wires and an old receiver first just to see whether it works straight from the receiver, if so try the other and if that works then supply the positive and negative from a separate 6v battery (5 cell 2800), looks a bit rickety and you don't want to compromise the power to your receiver and servos. If it doesn't work then I would source some new ones.

Someone who has experience with these retracts may have other ideas.

Attilio Rausse07/08/2020 15:56:50
118 forum posts

Changed my mind can't see any electronics, disregard what I have said you will need to source the control board.

Dale Bradly08/08/2020 06:14:29
43 forum posts
13 photos

If i owned these, this is what i would do:

1. Strip all the wiring and microswitches off the retracts.

2. Solder on a new 2-core lead direct to the motor terminals from an old modified as appropriate servo lead.

3. Get the Eflite 30cc Retract Controller Link

4. Plug one into the other.

5. If the current limits are requiring adjustment, get the retract programmer Link

I've got more than one set of retracts operating a similar conversion process, and work a treat, including on Eflite's own retracts where the inbuilt pcb seems to be the most unreliable part, hence i removed it from the equation.

The process in detail (different products): Link

Bob Cotsford08/08/2020 10:56:06
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8840 forum posts
496 photos

Brilliant! I have a few dead Eflite retract units, and if memory serves me, a retract controller that came with a cheap trike set that were too naff to use. Alternately JP Hobby market a nice range of retracts including various controllers. Time to experiment, there's nothing to lose as they're dead anywaysmiley

Denis Watkins08/08/2020 11:18:17
4655 forum posts
132 photos

Clean up those threaded drive shafts before applying current Jim

We get carried away with enthusiasm and miss things

There is some micro switch contacts protection shown in the pics but those components don't age well

You can get offload simple readings from your motor and switches with probes which would give you some idea

that the retracts are partially or wholly sound

Steve J08/08/2020 14:34:02
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2105 forum posts
61 photos

I don't know what was in the SM Services box, but you could do this with an Arduino and an H-bridge motor driver board.

Phil Green08/08/2020 21:09:14
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1664 forum posts
344 photos

You can do it much simpler than that and for much lower cost.

It looks like a simple DC motor driving a lead-screw with limit switches. Almost everything you need is already there. All you need is to be able to apply DC power in one direction (polarity) to raise them and the other polarity to lower them. The top diagram shows a simple switched reversing supply, the switch could be driven by a servo.

The lower diagram shows the wiring of the limit switches. With the power in one polarity it will drive one way until the limit switch breaks. With the power reversed it will drive the other way until the other limit switch breaks. The diodes allow the return current through the 'open' switch.  Arrange the motor terminals so it drives towards the appropriate limit switch, ie with pos on the left drives it towards the limit switch on the right and v.v.

Your only other job is to adjust the limit switch positions if necessary.

Cheers
Phil   

 

img_20200808_213659_252.jpg

 

 

 

 

Edited By Phil Green on 09/08/2020 09:54:23

jimmac12/08/2020 09:28:03
72 forum posts
5 photos
Posted by Phil Green on 08/08/2020 21:09:14:

You can do it much simpler than that and for much lower cost.

It looks like a simple DC motor driving a lead-screw with limit switches. Almost everything you need is already there. All you need is to be able to apply DC power in one direction (polarity) to raise them and the other polarity to lower them. The top diagram shows a simple switched reversing supply, the switch could be driven by a servo.

The lower diagram shows the wiring of the limit switches. With the power in one polarity it will drive one way until the limit switch breaks. With the power reversed it will drive the other way until the other limit switch breaks. The diodes allow the return current through the 'open' switch. Arrange the motor terminals so it drives towards the appropriate limit switch, ie with pos on the left drives it towards the limit switch on the right and v.v.

Your only other job is to adjust the limit switch positions if necessary.

Cheers
Phil

img_20200808_213659_252.jpg

Edited By Phil Green on 09/08/2020 09:54:23

Thanks Phil and all you other guys for your advice, I can now go and help the owner of them. He isn't too internet savvy to find the help you guys have given.

Richard Clark 212/08/2020 09:46:56
424 forum posts
Posted by jimmac on 12/08/2020 09:28:03:
Posted by Phil Green on 08/08/2020 21:09:14:

You can do it much simpler than that and for much lower cost.........

Cheers
Phil

Thanks Phil and all you other guys for your advice, I can now go and help the owner of them. He isn't too internet savvy to find the help you guys have given.

Yes. There is no need whatsoever to faff around with 'controllers' or 'Arduinos' and the like. Buying and figuring out how to program a computer for such a simple task is ridiculous.

Steve J12/08/2020 10:16:39
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2105 forum posts
61 photos
Posted by Phil Green on 08/08/2020 21:09:14:

You can do it much simpler than that and for much lower cost.

You have drawn an H-bridge with relays. Your way will have a servo driving a switch and the limit switches switching the motor current. I would go for an Arduino and an L293 (or other H-bridge circuit if more current is required) which would also allow control of the motor speed.

Bob Cotsford12/08/2020 11:15:38
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8840 forum posts
496 photos

The only thing not yet mentioned is to use a separate battery to drive the retracts if you use the limit switches so that if they stick and it drains the battery your radio doesn't die, with a commercial controller with built in current sensing you don't get this problem. They simply shut down if the controller senses a fault.

Richard Clark 212/08/2020 11:24:09
424 forum posts
Posted by Steve J on 12/08/2020 10:16:39:
Posted by Phil Green on 08/08/2020 21:09:14:

You can do it much simpler than that and for much lower cost.

You have drawn an H-bridge with relays. Your way will have a servo driving a switch and the limit switches switching the motor current. I would go for an Arduino and an L293 (or other H-bridge circuit if more current is required) which would also allow control of the motor speed.

They are not relays as they don't need coils. Merely two limit switches and two diodes (all of which are already there) and a double pole changeover switch and a servo. Even a nine or ten gramme servo will do.

As for speed, with screwjacks it will be 'slow' anyway and trying to make it slower it probably won't work at all as such jacks have extremely high friction.

As someone who has been a professional 'big' computer designer for over 35 years and am now working on the new 'post electronic' computers I strongly believe the use of a computer, and probably a bridge for something so simple is merely a modern 'knee jerk' fashion. In much the same as a Victorian engineer's first thought would be a steam engine plus boiler

Steve J12/08/2020 13:37:52
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2105 forum posts
61 photos

Posted by Richard Clark 2 on 12/08/2020 11:24:09:

As someone who has been a professional 'big' computer designer for over 35 years and am now working on the new 'post electronic' computers ...

Do you give out autographed photos with the highlights of your CV on the back?

EarlyBird12/08/2020 14:43:54
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507 forum posts
369 photos
Posted by Steve J on 12/08/2020 13:37:52:

Posted by Richard Clark 2 on 12/08/2020 11:24:09:

As someone who has been a professional 'big' computer designer for over 35 years and am now working on the new 'post electronic' computers ...

Do you give out autographed photos with the highlights of your CV on the back?

yeslaugh

Caveman12/08/2020 18:37:08
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320 forum posts
245 photos

The problem, as I see it, with the simple diagram, is if the u/c leg gets caught during retraction or deployment won't the motor try to keep driving it leading to increased current flow, heat and battery depletion?

I understand that the modern commercial, and probably Arduino, drivers look out for high current draw and stop the retract if this occurs. This seems like a better solution to me, or am I wrong?

GDB

Steve J12/08/2020 18:51:47
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2105 forum posts
61 photos

The electric retracts that I have (E-flight & HobbyKing) will stop if they haven't hit the limit switch within a certain amount of time. The E-flight suggested above would appear to be measuring the current and running until the motor stalls.

I had a look inside a cheap electric retract this afternoon. The board appears to have a microcontroller, four transistors, two limit switches and some passives on it .

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