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Author Topic: Crossover/limit switch diagram  (Read 3855 times)

Brian60

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Crossover/limit switch diagram
« on: November 10, 2014, 09:26:52 AM »

Many many years ago we used to have a limit switch made up of two micro switches. The idea was you wanted to move something back and forth (or roundy roundy) but once it moved to the limit a pin hit the microswitch and interrupted the power to the motor, diverting the live to a similar microswitch at the other end of your device.

You essentially had a device that travelled back and forth but only until the detent pins hit the microswitches, then it would stop, ready for a new signal to its motor for it to reverse direction, the switches basically reversed the motor polarity and turned it off when it reached its limit of travel.

Can anyone draw this circuit for me because for the life of me after 30 years my mind will not drag it out of the cupboard!

inertia

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Re: Crossover/limit switch diagram
« Reply #1 on: November 10, 2014, 09:53:17 AM »

This might help. Scroll down to "Limit Switches". It's the top diagram on the page.
DM

http://www.action-electronics.co.uk/wd.php

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Brian60

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Re: Crossover/limit switch diagram
« Reply #2 on: November 10, 2014, 10:30:22 AM »

I can't see anything on there Inertia, the top diagram is for an artesania latina model.

EDIT: found it! that is almost what I was after, I seem to recall being able to operate it from just a servo, back in the dim and distant past there was no such thing as Action controllers to stick in the circuit.

inertia

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Re: Crossover/limit switch diagram
« Reply #3 on: November 10, 2014, 11:26:50 AM »

Quite probably you can, but then you'd have four m***********s to connect up in circuit. Good luck with that.
DM
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Geoff C

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Re: Crossover/limit switch diagram
« Reply #4 on: November 13, 2014, 11:09:39 AM »

Hi Brian,    Is this what you mean,  from my  Grand Banks Schooner, and C.R.Jeffries book?     Regards  Geoff.
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Brian60

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Re: Crossover/limit switch diagram
« Reply #5 on: November 13, 2014, 02:05:51 PM »

Nice model there Geoff and I think your diagrams are exactly what I am after. Just a servo to nudge a contact to operate a motor in one direction, then the switches to turn it off at the limit and then it can travel in the opposite direction with another nudge of the servo contact.

In my case I want to raise and lower two towing pins that are set flush to my deck, so the principle is the same

Many thanks.

flashtwo

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Re: Crossover/limit switch diagram
« Reply #6 on: November 14, 2014, 04:43:32 PM »

Hi Brian,

Would it be too involved to use a pair of 3-pole relays as part of the logic to give exactly what you want.

I assume that you don't want a split supply to give bi-directional motor movement, so I've devised a circuit with single supply rails.

If you don't mind having relays, I'll do a diagram (rather than a sketch) and post it.

Do you remember if the original system used a mechanical linkage with a lot of backlash for operating the micro-switches? It is one way for a system to "remember" which direction it is travelling.

Ian

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inertia

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Re: Crossover/limit switch diagram
« Reply #7 on: November 14, 2014, 06:40:04 PM »

Ian
I think that ACTion may have beaten you to it by a few years. If the choice is between microswitches on top of servos and anything else then the die is already cast. You can't win them all. Move on, dude.
Dave M
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Brian60

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Re: Crossover/limit switch diagram
« Reply #8 on: November 14, 2014, 08:52:15 PM »

Dave its ok to keep on about Action but I took a look at the Components website who are now the sole distributor for them. A number of the units are marked as 'Out of Stock' I sent an email to see when they will be back in stock but I'm waiting an answer. The unit you mentioned first is one of those that are out of stock.

Its a shame because I was almost at the point of deciding that Action would be the electronics to go for, but as I would buy them as and when they needed to be installed, I'm concerned that I could lay out some serious money only to find that one or more units may no longer be produced once I have already bought 2 or 3.

flashtwo

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Re: Crossover/limit switch diagram
« Reply #9 on: November 14, 2014, 09:52:14 PM »

Hi Dave M,

Ouch!

I've actually got a servo substitute PIC based circuit that I designed, coded and built 7 years ago. It inputs the 1-2ms PWM and outputs via relay contacts. I use it on my 42" RAF Crash Tender for operating the fire monitor water pumps and it is also programmed to morse code flash the on-board search light for any message required to be transmitted; currently it is programmed to morse code "Grace Darling" for when it was displayed at an RNLI model boat meeting.

I think I may beaten ACTion to it. I have chatted to Dave of ACTion on several occasions and his general products are fine, but obviously he doesn't do specials. A recent example of a special application is covered under the "Help Writing PIC code" where Megatron  has made a sterling effort in coming to grips with PIC coding.

No, seriously, some people prefer to keep things within the realms of their understanding and using relays and servo operated microswitches makes things more visual and removes the mystery of coded devices.

There are pros and cons for any solution - but don't forget the old relay logic it still has its uses.

Ian

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inertia

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Re: Crossover/limit switch diagram
« Reply #10 on: November 14, 2014, 11:27:28 PM »

Brian
The units are made in-house so they should only be out of stock for a day or so. It's not like having to wait until the Chinese ship another palette. A phone call will usually set the wheels of production back in motion - once Lyn's had her tea, that is.

Flash
Doing 'specials' might be interesting but for a manufacturer it's commercial madness, especially for the sort of money that retail customers would be prepared to pay. Dave of ACTion would tell you just the same thing.

Dave M
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malcolmfrary

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Re: Crossover/limit switch diagram
« Reply #11 on: November 15, 2014, 10:36:20 AM »

Since the job is to raise and lower lifting pins, I can't help wondering if this is a job for a servo to do the job directly, or via a linkage operating a cam.
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flashtwo

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Re: Crossover/limit switch diagram
« Reply #12 on: November 15, 2014, 11:30:03 AM »

Hi Dave M,

Yes, I agree with you; I remember Dave saying the same thing when he saw my Flash Steam Boiler controller with it half-a-dozen PICs. Its not just producing the item, but also the longer term support.

People often ask me the price of my Flash Steam boiler controller. The actual hardware can be made in a fortnight, but the software code took several years to fully develop. Its relatively easy to calculate the price of the hardware, but the software would run into thousands of pounds, if each line of code was worth even 10p. In no way would it make commercial sense unless, that is, there were thousands of flash boiler customers out there. That's the beauty of a hobby - there are few people (except one!) that you have to justify the cost.

Anyway, we must come to a solution for Brian's current requirement.

Ian
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inertia

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Re: Crossover/limit switch diagram
« Reply #13 on: November 15, 2014, 01:22:29 PM »

Anyway, we must come to a solution for Brian's current requirement.
Ian

I think he's on the brink of ordering the P44 Twin Relay Switch, which is now apparently back in stock.
Ref one-offs, no-one could beat Pete Keirle (PMK) at doing them, and he enjoyed it so much. I miss him a lot.
Dave M
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Brian60

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Re: Crossover/limit switch diagram
« Reply #14 on: November 15, 2014, 02:02:46 PM »

Malcolm I fail to see how you could raise and lower  two towing pins in the deck by a set amount just with a servo. What is to stop the servo trying to push them to high above the deck, or even pulling them through the deck when retracting them?

inertia

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Re: Crossover/limit switch diagram
« Reply #15 on: November 15, 2014, 02:44:37 PM »

Maybe something like this? Cams shaped to set travel etc.

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flashtwo

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Re: Crossover/limit switch diagram
« Reply #16 on: November 15, 2014, 02:47:59 PM »

What about using  ACTion's Servomorph P96, you could control the servo limits and also the speed.


Ian
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malcolmfrary

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Re: Crossover/limit switch diagram
« Reply #17 on: November 15, 2014, 04:46:13 PM »

Malcolm I fail to see how you could raise and lower  two towing pins in the deck by a set amount just with a servo. What is to stop the servo trying to push them to high above the deck, or even pulling them through the deck when retracting them?
You already know how much travel is wanted.  The servo arm moves a set distance, so its just a case of deciding which hole on the arm to link to.  Or use something like Daves very elegant suggestion with the right size cam.  When it comes down to it, a servo is a motor and gearbox with a control unit added.  Sometimes extra control or more power is needed, but the extra layer here just looks redundant.  I'm not a flyer, but do not "retract" servos do this exact function under control of a switch on the transmitter which just sends a "be here" or "be there" signal?
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Brian60

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Re: Crossover/limit switch diagram
« Reply #18 on: November 15, 2014, 05:54:57 PM »

Thanks for the illustration Dave, I see now. However using that method I can see the pins raising but then you are relying on their own weight to retract, there is not a lot of weight in two pieces of 20mm brass tube. Although thinking further the solution could be to have two springs in tension on the lower ends of the tube.

inertia

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Re: Crossover/limit switch diagram
« Reply #19 on: November 15, 2014, 07:52:28 PM »

Like this? As Malcolm would say, if you want to find out how many ways there are to skin a cat then first you need to define "cat". He is a smart cookie, our Malc......
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