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Ground Contact Sensor for SES Tubing Leg.

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Posted: 2010-01-11 16:22 
Here is my idea for the SES Ground Contact Sensor.

The diagram shows the Leg as is would be for Zentas T-Hex. This new leg adds only .50" (12.7mm) to the length. It's truly as small as I could reasonably get it. The switch is basically where the insulated Foot Pad aluminum part touches the lip of the Foot Hub. The spring is lightly loaded in the open position. The travel can be adjusted to a hairs width. I'm shooting for 0.031" in the drawing. Any dirt that was able to enter the open area inside would fall out, as there is nothing to keep it in there. There are lots of stock springs that will fit inside. There are also different wire sizes and wire materials to choose from.

This will require the design of two aluminum hubs and a ss shaft. The rest are all off the shelf components.

I don't like that the chassis itself must be grounded to use the sensors. But that's the only downside to this design. As usual, feedback is welcome.
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footswitchcutaway.gif
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Posted: 2010-01-11 17:44 
Not sure of intent of screw into foot hub were it contacts nylon shoulder washers. You've indicated the contact closure to be down between foot and hub, however it could also be accomplished between the two nuts and the top hub if spacings were adjusted. Keeps contact in-closed, and out of the dirt.

Alan KM6VV

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Posted: 2010-01-11 17:48 
Very interesting design Jim!
Robot Dude wrote:
The switch is basically where the insulated Foot Pad aluminum part touches the lip of the Foot Hub. The spring is lightly loaded in the open position. The travel can be adjusted to a hairs width. I'm shooting for 0.031" in the drawing. Any dirt that was able to enter the open area inside would fall out, as there is nothing to keep it in there.


Are you really sure that walking in very wet dirt won't make the contact/switch a little unstable? I'm pretty sure it would work pretty good under "normal" conditions though. Adding some sort of RC filter and maybe a schmitt trigger for smoothing out ripple/noise too? :|

I do have a feeling that a very small microswitch would be more reliable than the aluminium contact switch.

Have to admit I don't have much experience in how reliable these kind of switches are.

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Posted: 2010-01-11 18:21 
KM6VV wrote:
Not sure of intent of screw into foot hub were it contacts nylon shoulder washers. You've indicated the contact closure to be down between foot and hub, however it could also be accomplished between the two nuts and the top hub if spacings were adjusted. Keeps contact in-closed, and out of the dirt.

Alan KM6VV


That screw holds the sensor in the tube. Without it the whole assembly would slide right out of the tube.


EDIT: I totally misunderstood your suggestion. I rewrote my reply...

This example is for the shortest aluminum tube we offer. We plan to use this sensor on tibias made from longer tubing. So even if it would work for this leg, it wouldn't work for the longer ones. However If I made these parts there is nothing preventing modification to move the switch up inside the tube though. I mean the hard parts would be done anyway.

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Posted: 2010-01-11 18:26 
zenta wrote:
Very interesting design Jim!


I think it's a start anyway. :P

zenta wrote:
Are you really sure that walking in very wet dirt won't make the contact/switch a little unstable? I'm pretty sure it would work pretty good under "normal" conditions though. Adding some sort of RC filter and maybe a schmitt trigger for smoothing out ripple/noise too? :|


I didn't say wet dirt, just normal dry dirt. lol

zenta wrote:
I do have a feeling that a very small microswitch would be more reliable than the aluminium contact switch.

Have to admit I don't have much experience in how reliable these kind of switches are.


I'm not giving up on the other design (hybrid), just trying to close the loop on the SES tubing leg. As long as the parts are not anodized it should work reliably.

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Posted: 2010-01-12 10:09 
I love the design! Brilliant!

Very robust design! Might need some light weight oil during assembly to keep the assembly from "sticking" although it is riding on nylon inserts so It might not be nessasary.

I love it!!



Robot Dude wrote:
Here is my idea for the SES Ground Contact Sensor.

The diagram shows the Leg as is would be for Zentas T-Hex. This new leg adds only .50" (12.7mm) to the length. It's truly as small as I could reasonably get it. The switch is basically where the insulated Foot Pad aluminum part touches the lip of the Foot Hub. The spring is lightly loaded in the open position. The travel can be adjusted to a hairs width. I'm shooting for 0.031" in the drawing. Any dirt that was able to enter the open area inside would fall out, as there is nothing to keep it in there. There are lots of stock springs that will fit inside. There are also different wire sizes and wire materials to choose from.

This will require the design of two aluminum hubs and a ss shaft. The rest are all off the shelf components.

I don't like that the chassis itself must be grounded to use the sensors. But that's the only downside to this design. As usual, feedback is welcome.
Attachment:
footswitchcutaway.gif

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Posted: 2010-01-12 15:15 
I got that the screw's intent was to hold the insides in. What I was questioning (suggesting) is that the diameter of the screw meets the ratty edge of the two nylon shoulder washers. Is it intended to contact the shoulder washers? I'll assume that you don't want it to contact the green shaft. And also that it threads into the blue body.

Have you seen screws in SES tubing and hubs work themselves out? I'd suggest a split lock washer, or perhaps Locktite.

But looks like a workable plan all considered.

Alan KM6VV

Robot Dude wrote:
KM6VV wrote:
Not sure of intent of screw into foot hub were it contacts nylon shoulder washers. You've indicated the contact closure to be down between foot and hub, however it could also be accomplished between the two nuts and the top hub if spacings were adjusted. Keeps contact in-closed, and out of the dirt.

Alan KM6VV


That screw holds the sensor in the tube. Without it the whole assembly would slide right out of the tube.


EDIT: I totally misunderstood your suggestion. I rewrote my reply...

This example is for the shortest aluminum tube we offer. We plan to use this sensor on tibias made from longer tubing. So even if it would work for this leg, it wouldn't work for the longer ones. However If I made these parts there is nothing preventing modification to move the switch up inside the tube though. I mean the hard parts would be done anyway.

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Posted: 2010-01-12 15:35 
KM6VV wrote:
I got that the screw's intent was to hold the insides in. What I was questioning (suggesting) is that the diameter of the screw meets the ratty edge of the two nylon shoulder washers. Is it intended to contact the shoulder washers? I'll assume that you don't want it to contact the green shaft. And also that it threads into the blue body.

Have you seen screws in SES tubing and hubs work themselves out? I'd suggest a split lock washer, or perhaps Locktite.

But looks like a workable plan all considered.

Alan KM6VV


The screws are not purposely drawn to make contact with the shoulder washers, I just didn't pay that much attention to that part of the drawing. I have seen Phoenix leg segments work loose from the aluminum servo horns if not tightened down properly, but I have not seen any other cases.

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Posted: 2010-01-12 16:33 
So it looks like the foot hub, the SS shaft, and the foot pad are 3 components that need to be machined right?

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Posted: 2010-01-12 16:45 
Yeah, we can do that! Sherline! ;>)

Also the nylon shoulder washers (might be stock) and a spring to spec.

I'll wait for the kits, if they don't take too long, I'll need four (4) for my 'quad!

SN96 wrote:
So it looks like the foot hub, the SS shaft, and the foot pad are 3 components that need to be machined right?


Alan KM6VV

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Posted: 2010-01-12 17:02 
KM6VV wrote:
Yeah, we can do that! Sherline! ;>)

Also the nylon shoulder washers (might be stock) and a spring to spec.

I'll wait for the kits, if they don't take too long, I'll need four (4) for my 'quad!

SN96 wrote:
So it looks like the foot hub, the SS shaft, and the foot pad are 3 components that need to be machined right?


Alan KM6VV


Yes the nylon washers and the spring are standard components. I'm sending the drawings off hopefully today. Shouldn't be but a couple weeks.

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Posted: 2010-01-12 20:15 
It is an interesting exercise in making small parts, but I think it has a somewhat limited potential due to simpler and cheaper ways to get the same job done.

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Posted: 2010-01-12 20:26 
Just a thought, a Hall-effect device like the Allegro A3213/14 would be a good way to implement the "switch' as well. A good Samarium cobalt magnet would be needed, however.

Alan KM6VV

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Posted: 2010-01-13 10:37 
zoomkat wrote:
It is an interesting exercise in making small parts, but I think it has a somewhat limited potential due to simpler and cheaper ways to get the same job done.


There are simpler and cheaper ways to do the same thing? The job at hand is to provide a strong leg segment based on the SES tubing that can detect contact with the ground with minimal side effects. This can't be done with a paper clip and a Popsicle stick. This design also has the advantage that the tip of the foot can rotate which will minimize the main source of friction with three DOF legs. If there truly are simpler and cheaper ways to get the same job done, well... show me. ;)

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Posted: 2010-01-13 10:46 
KM6VV wrote:
Just a thought, a Hall-effect device like the Allegro A3213/14 would be a good way to implement the "switch' as well. A good Samarium cobalt magnet would be needed, however.

Alan KM6VV


Can it really be set up to work reliably with only 0.03" of travel in the shaft?

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