Mk2 Lever frame and Microswitches

Discussions of the prototypes and how to model them. Show us how you do it.
junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Mk2 Lever frame and Microswitches

Postby junctionmad » Wed Jul 25, 2018 5:16 pm

Having completed 2 levers of the first 5 , of 55!, I decided to try the microswitches

My microswitches are " standard " from Farnell with rollers etc, The nature of the fret is that the roller must not extend beyond the body of the microswitch

What I am finding , and for me these frames are electric only , is that the microswitch switches in a very short range typically 5-8mm of the lever travel , i.e. at around 60%,40% , depending on where I position the micro switch frame I can move that 5-8mm anywhere , but I cant arrange a situation where the switching occurs around 80% and 20 % of travel which would be ideal. I even bent the roller arm a bit , to see if I could improve things , but the switch range remains constant. The fundemental issue being the roller contacts too low on the lever arm , its really needs to be very very close to the pivot point, These microswitches switch in less then 1mm of movement even with the arm . I think the whole things needs longer arm microswitches but this leaves positioning the microswitch etch more problematic as it would have to be on a different level to the frame

I think the microswitch situation needs more thought personally , as there isnt a lot of room to do anything , optical switching might be better

Dave

JFS
Posts: 570
Joined: Wed Dec 16, 2009 3:47 pm

Re: Mk2 Lever frame and Microswitches

Postby JFS » Wed Jul 25, 2018 7:24 pm

junctionmad wrote:What I am finding , and for me these frames are electric only , is that the microswitch switches in a very short range typically 5-8mm of the lever travel , i.e. at around 60%,40% , depending on where I position the micro switch frame I can move that 5-8mm anywhere , but I cant arrange a situation where the switching occurs around 80% and 20 % of travel which would be ideal.


Hello Dave,

They are designed to switch at between 70 and 80% and mine have all been fine. Can you post a photo so we can see what is going wrong please?

Regards,

junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Re: Mk2 Lever frame and Microswitches

Postby junctionmad » Wed Jul 25, 2018 7:39 pm

JFS wrote:
junctionmad wrote:What I am finding , and for me these frames are electric only , is that the microswitch switches in a very short range typically 5-8mm of the lever travel , i.e. at around 60%,40% , depending on where I position the micro switch frame I can move that 5-8mm anywhere , but I cant arrange a situation where the switching occurs around 80% and 20 % of travel which would be ideal.


Hello Dave,

They are designed to switch at between 70 and 80% and mine have all been fine. Can you post a photo so we can see what is going wrong please?

Regards,



The issue is I would really like a longer travel between switching , i.e. a longer roller lever , or a contact point closer to the frame lever pivot , i.e. so that I could get more then 10% travel between switching

Its not a show stopper , I can move the microswitches so that I get your 60% 40& (or close enough ) ,

Pics show two switching positions ( its all a temporary lashup)
IMG_0019.jpg

IMG_0020.jpg


dave

TEZBEDZ
Posts: 53
Joined: Thu Sep 04, 2008 3:36 pm

Re: Mk2 Lever frame and Microswitches

Postby TEZBEDZ » Wed Jul 25, 2018 9:53 pm

I am about to build a lever frame using the microswitches.
I was wondering if someone could help me with the wiring of these switches. I shall be using them to switch servos using a MERG Servo4. These are currently switched by on/off switches with two terminals. The microswitches have 3 terminals. Help! Not sure how to make this work
I should apologise for hijacking this thread
Regards

Terry

User avatar
grovenor-2685
Posts: 2952
Joined: Sun Jun 29, 2008 8:02 pm

Re: Mk2 Lever frame and Microswitches

Postby grovenor-2685 » Wed Jul 25, 2018 10:17 pm

The issue is I would really like a longer travel between switching , i.e. a longer roller lever , or a contact point closer to the frame lever pivot , i.e. so that I could get more then 10% travel between switching

Microswitches are specifically designed to switch quickly, to get what you want you would have to use two switches per lever, or design some additional mechanics to create the required hysteresis. Neither option will be particularly easy with these frames.
Regards

User avatar
grovenor-2685
Posts: 2952
Joined: Sun Jun 29, 2008 8:02 pm

Re: Mk2 Lever frame and Microswitches

Postby grovenor-2685 » Wed Jul 25, 2018 10:20 pm

TEZBEDZ wrote:I am about to build a lever frame using the microswitches.
I was wondering if someone could help me with the wiring of these switches. I shall be using them to switch servos using a MERG Servo4. These are currently switched by on/off switches with two terminals. The microswitches have 3 terminals. Help! Not sure how to make this work
I should apologise for hijacking this thread

The three contacts are a common, a normal and a reverse, you just ignore the normal so your two wires are connected between the common and the reverse when the lever is pulled.
Regards

JFS
Posts: 570
Joined: Wed Dec 16, 2009 3:47 pm

Re: Mk2 Lever frame and Microswitches

Postby JFS » Thu Jul 26, 2018 5:53 am

junctionmad wrote:The issue is I would really like a longer travel between switching , ... so that I could get more then 10% travel between switching

Its not a show stopper , I can move the microswitches so that I get your 60% 40& (or close enough ) ,

dave


Hello Dave,

Ah - Keith's post has helped me to understand your query - thanks Keith!

As he says, the microswitches change over instantaneously. From your photo, you have set the switching point to be very close to the "normal" position, whereas they are designed to switch when the lever is 80% towards the reverse position. Given the tolerance in building everything, some levers will switch a bit earlier and some a bit later but all will be within a fairly tight range and each individual lever will operate instantaneously. Bending the switch lever is not necessary to achieve that result, whereas bending it as you have will make the switching earlier, but you might run out travel when the lever is fully over.

On my frame, I have arranged to drive the switches off the mechanical locking which gives much finer control, and enables the fitting of two switches to give the "Not normal" and the "Not reverse" switching positions you seek, but this is not an option for everyone. However, if you really need that functionality and given that you do not need a mechanical take-off, you can create a simple cam, using the top clevis provided in the kit, to operate one switch at one end of the stroke and the other one at the opposite end.

If this is of interest, I can post a simple sketch showing how this is done.

Hope that helps.

junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Re: Mk2 Lever frame and Microswitches

Postby junctionmad » Thu Jul 26, 2018 10:29 am

JFS wrote:
junctionmad wrote:The issue is I would really like a longer travel between switching , ... so that I could get more then 10% travel between switching

Its not a show stopper , I can move the microswitches so that I get your 60% 40& (or close enough ) ,

dave


Hello Dave,

Ah - Keith's post has helped me to understand your query - thanks Keith!

As he says, the microswitches change over instantaneously. From your photo, you have set the switching point to be very close to the "normal" position, whereas they are designed to switch when the lever is 80% towards the reverse position. Given the tolerance in building everything, some levers will switch a bit earlier and some a bit later but all will be within a fairly tight range and each individual lever will operate instantaneously. Bending the switch lever is not necessary to achieve that result, whereas bending it as you have will make the switching earlier, but you might run out travel when the lever is fully over.

On my frame, I have arranged to drive the switches off the mechanical locking which gives much finer control, and enables the fitting of two switches to give the "Not normal" and the "Not reverse" switching positions you seek, but this is not an option for everyone. However, if you really need that functionality and given that you do not need a mechanical take-off, you can create a simple cam, using the top clevis provided in the kit, to operate one switch at one end of the stroke and the other one at the opposite end.

If this is of interest, I can post a simple sketch showing how this is done.

Hope that helps.


Thanks Howard , I would appreciate a sketch , I was just pondering using the etches remaining to achieve dual switching ,

Ps , my selected switching position and moving the roller arm closer to the pivot was to increase the hysteresis, personally I would prefer 60 /40 over 80%

JFS
Posts: 570
Joined: Wed Dec 16, 2009 3:47 pm

Re: Mk2 Lever frame and Microswitches

Postby JFS » Thu Jul 26, 2018 12:16 pm

junctionmad wrote:
Thanks Howard , I would appreciate a sketch , I was just pondering using the etches remaining to achieve dual switching ,

Ps , my selected switching position and moving the roller arm closer to the pivot was to increase the hysteresis, personally I would prefer 60 /40 over 80%



Hi Dave,

Give me a day or two and I will knock something up.

It is easy enough to reduce below 80% just by moving the switch bracket further away from the frame - best thing is to experiment, then make a template for drilling the base once you have the locations fixed.

Best Wishes,

User avatar
Colin Parks
Posts: 557
Joined: Sun Oct 27, 2013 4:44 pm

Re: Mk2 Lever frame and Microswitches

Postby Colin Parks » Thu Jul 26, 2018 6:38 pm

Is it just me, or is the lever nearest the camera not in its slot. If it is not, that could be the cause of the problem with the micro switches.

junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Re: Mk2 Lever frame and Microswitches

Postby junctionmad » Thu Jul 26, 2018 8:38 pm

Colin Parks wrote:Is it just me, or is the lever nearest the camera not in its slot. If it is not, that could be the cause of the problem with the micro switches.

It’s in its slot

Dave

User avatar
Colin Parks
Posts: 557
Joined: Sun Oct 27, 2013 4:44 pm

Re: Mk2 Lever frame and Microswitches

Postby Colin Parks » Thu Jul 26, 2018 9:40 pm

Hello Dave,

Yes, I can see now the lever is in its slot! The shape of the metal lever on your micro-switch looks different to mine (seen here as a common crossing polarity switch):

IMG_8912 (2).JPG
IMG_8912 (2).JPG (51.58 KiB) Viewed 438 times


Perhaps your switch started out with a straight lever, but as it is now, it appears almost closed without pressure on the roller.

Colin

JFS
Posts: 570
Joined: Wed Dec 16, 2009 3:47 pm

Re: Mk2 Lever frame and Microswitches

Postby JFS » Thu Jul 26, 2018 10:47 pm

Hello Dave,

As promised I have had a quick look at how to achieve what you seem to be after. Of course, this is nothing more than a sketch and I suspect that there are better ways of doing it, but it would work. As you can see, I am suggesting attaching a simple cam (made from a bit of fret waste - similar to the one in Colin's photo) to the end of the top clevis which comes in the kit. This is supported in such a way that the cam can resist the action of the switch. The cam is bent in such a way that the NC contact on the switch opens as soon as the lever leaves one end of its travel, and closes again as it arrives at the opposite end. By wiring this switch in series with the one actuated by the lever, you will get the appropriate output.

Switch Sketch.jpg
Switch Sketch.jpg (131.95 KiB) Viewed 429 times


Obviously, you will want to refine this and no doubt come up with a better solution, but it should work alright and be simple enough to make.

All of this reminds me why I do the locking mechanically...

Just also to mention that the sketch also shows how the microswitch is designed to operate. It took a lot of effort to get the geometry right and I am surprised it is giving you trouble - I have fitted almost 100 of these and they all work perfectly.

Regards,

junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Re: Mk2 Lever frame and Microswitches

Postby junctionmad » Fri Jul 27, 2018 3:18 am

JFS wrote:Hello Dave,

As promised I have had a quick look at how to achieve what you seem to be after. Of course, this is nothing more than a sketch and I suspect that there are better ways of doing it, but it would work. As you can see, I am suggesting attaching a simple cam (made from a bit of fret waste - similar to the one in Colin's photo) to the end of the top clevis which comes in the kit. This is supported in such a way that the cam can resist the action of the switch. The cam is bent in such a way that the NC contact on the switch opens as soon as the lever leaves one end of its travel, and closes again as it arrives at the opposite end. By wiring this switch in series with the one actuated by the lever, you will get the appropriate output.

Switch Sketch.jpg

Obviously, you will want to refine this and no doubt come up with a better solution, but it should work alright and be simple enough to make.

All of this reminds me why I do the locking mechanically...

Just also to mention that the sketch also shows how the microswitch is designed to operate. It took a lot of effort to get the geometry right and I am surprised it is giving you trouble - I have fitted almost 100 of these and they all work perfectly.

Regards,

Thanks re sketch , I had similar thoughts , personally I’m looking at a pcb that would hold tactile switch’s so that the high level Clevis worked two switches via a sliding profile attached to the upper take off. This would completely remove any issues with exact micro switch positioning

I don’t think “ standard “ micro switches are all that “ standard”. My ones do not make contact with the lever exactly as per your sketch, n fact the exact length of the roller arm seems to vary quite a bit across a range of microswitches
Last edited by junctionmad on Fri Jul 27, 2018 3:35 am, edited 1 time in total.

junctionmad
Posts: 191
Joined: Tue Dec 08, 2015 3:38 pm

Re: Mk2 Lever frame and Microswitches

Postby junctionmad » Fri Jul 27, 2018 3:31 am

Colin Parks wrote:Hello Dave,

Yes, I can see now the lever is in its slot! The shape of the metal lever on your micro-switch looks different to mine (seen here as a common crossing polarity switch):

IMG_8912 (2).JPG

Perhaps your switch started out with a straight lever, but as it is now, it appears almost closed without pressure on the roller.

Colin

Initially this microswitch ( farnell ) had a straight lever to the roller , this meant the roller contacted the lever near the tip,of the lever , this caused issues with the switch point as the throw was too much imho , so I bent the roller lever so that the roller contacted closer to the pivot of the frame lever , ie where there is less throw , that’s what you see in the pictures

Dave

JFS
Posts: 570
Joined: Wed Dec 16, 2009 3:47 pm

Re: Mk2 Lever frame and Microswitches

Postby JFS » Fri Jul 27, 2018 6:42 am

junctionmad wrote:Initially this microswitch ( farnell ) had a straight lever to the roller , this meant the roller contacted the lever near the tip,of the lever , this caused issues with the switch point as the throw was too much imho , so I bent the roller lever so that the roller contacted closer to the pivot of the frame lever , ie where there is less throw , that’s what you see in the pictures

Dave


Hello again Dave,

You should be able to more consistently achieve the same effect by packing up the switch mounting bases with washers - there are quite a few spares provided on the frame fret.

You are no doubt right about variations in switches from different suppliers - though the ones from the stores seem consistent enough.

Regards,


Return to “Signals and Control Systems”

Who is online

Users browsing this forum: No registered users and 1 guest