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Very odd picture, Jim.
Unless, of course, you meant to make those feet miniature flashlights.



I don't suppose that you've got any plans for adding a similar bracket to the SES?

Speaking of that, I need to figure out how I'm going to attach my FSR's to my biped.

(I'd rather not revert to glue.)

Any ideas?

me != Jim

At least I think you were talking about my flashlight looking feet.

I did find in the plumbing department what look now to be the same copper connectors Matt used, but couldn't find the little rubber balls to fit well inside them. My other concern was on how to attach the copper tube to the leg without compromising the ability of the ball to move freely. Is that heat shrink?

Ugh!

Sorry, Andy.
I guess that I should look at the name next to the posts.



All parties, please ignore my above post.

I'm not a robot guy (yet!) by any stretch, nor am I much of a software guy (yet!), but for some reason I've been giving some thought to this particular problem and I've got an idea that might be a solution. When I get home tonight and have the time to go into more detail I'll try spelling it out as best I can.

The short version theory involves some variable resistors and spring loaded feet. I've seen variable resistors that are long and rectangular instead of round. These had a little tab that sticks out the side, which when moved changes the resistance.

Suppose you mount the resistor inside a hollow leg and let the "tab" protrude through a slot in the leg. Next you slip a sleeve over your hollow leg and have it spring loaded. This sleeve would capture the tab in some fashion. When the weight of the bot is placed on this foot (sleeve) the spring compresses somewhat and consequently slides the tab, changing the resistance. It seems this would be a decent solution in that as one or more feet are lifted, down pressure on the rest of the feet increases and resistance/pressure changes throughout the system of legs. Wouldn't this give you more than a "down or not down" reading for your legs, and help eliminate some of the problems with sensors being either too sensitive or not sensitive enough?


A little bit of spring tuning and it seems you would have nice viable system for foot position/pressure feedback.

Of course, I don't know squat about robotics or software problems so I might be sounding like a complete idiot here. Don't be afraid to say so.

I have revisited my foot sensor idea, and it now works reliably!

The original idea was to use the Interlink 0.20" FSR. It has adhesive on one side. It is attached to the flat of the HUB-09, a rubber bumper goes on top, and a rubber end cap goes over the whole thing. The original try used a 0.50" ID end cap on the 0.50" OD tubing. It would work, sorta, but it wouldn't zero out reliably when the foot was lifted. I just received some rubber end caps with a 0.563" ID to try. I used a 4-40 button head screw to hold the tubing onto the HUB-09. There is enough friction to hold the rubber end cap onto the end of the leg, but due to the slightly larger ID it no longer has the issue of not zeroing out when lifted. It starts to register at about 150kohm with as little as 1.6 oz. of pressure. The sensor is has a range of about 5lbs I think. The pressure can be at an angle as well. The rubber end cap protects the FSR and the leg still retains it's rugged properties.

Note: Image does not include the Interlink FSR.

That's great. Will you be adding the 0.53" end-caps to the catalog?

I'll post some pictures of my solution to this problem soon. Basically I used the existing alumininum tubing for the leg, a spring, magnet, and a linear hall effect sensor. Think of an inverted ball point click pen. I am getting consistent voltage readings from the HES and am accurately predicting how much force/weight is on a given leg at a particular point in time.

I am considering making a batch of these for those who do not have machining tools at home.

Mark K

Mark,

I'd be interested to see what you have got working. I've been experimenting with a conductive rubber solution, but I am open to other approaches. My expertise is mostly on the software end.

WalkThisWay,

Here's a pic of what I have put together. The components on the right top is the hall effect sensor. And below that is a high intensity magnet

I'm down! Depending on the cost, I think I'd be very interested in getting in on that. Seems a very elegant and robust solution.

Stalk

I'm very interested in your solution. Let me know what you need.

That looks nice! What are the interface requirements and what would it cost?

I too have interest. This is a well thought out solution. How exactly are the internal components arranged? - a simple sketch would suffice. Thanks in advance

Chris

Thanks,

I still have a couple of kinks to work out first. Such as tightening up the tolerances of the prototypes and trying some different springs to vary the air gap.

Here's the datasheet for the HES: http://www.melexis.com/prodfiles/000475 ... Rev007.pdf

Here's a good document explaining the operation of the device: http://www.melexis.com/prodfiles/0003715_hallapps.pdf


And here's a screen capture from wildfire showing the components internal structure:


I also need to work on simplifying the structure as right now it would run about $40 / per to manufacture. Almost half of which is the HES since I do not have the Melexis programmer and have not invested the time to design my own.
As far as to the interface I simply connect the wires to a MAX 127 ADC and measure the voltage drop as the air gap varies. The HES is programmed at 100MV/MT @ 2.5V

Let me know if you have any questions

Thanks
Mark Klunder

I failed to mention that the Max127 has an I2C Interface.
Which connects to my Gumstix "Brain" Like Andy my bot is rather "dumb" in that I controll it over an 802.11 connection.

Mark K