Uh-oh. My bad, don't want no forum trouble, especially from my hero Mike Green... I better come clean: long wraparound perimeter bumper is a potentiometer switch. Any contact is readable on one pin, ADC or RCtime tells you where you're hitting. Hi resolution yields accurate object location and is much simpler than having many many many individual bump switches.
Edit: Can we pretend I didn't make such a dumb joke? Apparently by sense of humor has already gone to sleep. It's time for the rest of me to follow. I wish it weren't against my religion to delete posts or I'd delete this one.
These are good, but there are a couple of issues to consider:
1. The SoftPots aren't sealed, so be careful using them outdoors. They sell a HotPot line, which are sealed, but these require more pressure to actuate.
2. Very hard impacts will permanently damage the membrane. You'd be wise to put the strip within a recess so that it won't take the full force of hit.
3. It's not possible to read multiple contact points. It will register the nearest point only. (One way around this is to use a second strip, mounted in reverse direction. Then you can tell if there's at least two separate contact points. This is a pretty expensive route, though.)
I think they're fine as a failsafe for when proximity detection missed an object. Given a one meter strip, and assuming one loop around the robot's base, I'm guessing a one foot diameter bot. That's no bantam weight. With that kind of mass, given any speed at impact your SoftPot may not last long. So be gentle to it!
You might also consider putting some foam on the outside as a cushion. I don't know how that will affect its sensitivity, but it would probably help it to last longer in the Erco household.
Maybe running a ring of vinyl tubing around the outside of the SoftPot? It might be possible to get some that's rigid enough to give a good contact and soft enough to protect the SoftPot.
You boys are right on frequency. The Softpots are fragile, if they get kinked or hit too hard I suspect that's the end of them. Digikey shipped it to me STRAIGHT in a huge box, 4 feet long by ~10" triangular cross section. Seems like overkill. How about a mailing tube?
I'm not a huge fan of circular robots, but yes, this one will be 13" diameter to keep the bend as gentle as possible. And the plan is to have vinyl or surgical tubing all the way around for protection.
In my case not sharp, just wise (been there, done that wise).
Something that would expand the surface area of a bump vertically but not so much horizontally would probably benefit the SoftPot. The combination of the recess and the tube could help prevent the strip from the full force of the impact. As the tube compresses it spreads out to the recess, filling it, and preventing the object from going any deeper -- the object hits the ridges of the recess as a hard stop.
Maybe you could find an inner tube that's the right size. Steal the one from your kid's first bicycle, maybe. Fill it up to the pressure that still registers the bumps in more or less the right spots.
Yes, it only indicates the lowest resistance. It's quite sensitive, any outer protective tubing can't be tight or under tension. A loose fit that only presses when it hits a wall or object.
Thats a tough one..
Sounds like split one edge of the tube and attach only on the top side.?
At first I thought about expanding foam behind the sensor as a shock absorber,
but that does not help solve the "it can't touch the sensor face" part of the problem.
Easy enough to draw...
looks like it will take some very flexible and thin surgical tubing..
edit: Scratch the expanding foam, and think weatherstripping instead..
Hrmm, gonna have to think outside the circle for this. Can't wait to see what you come up with..
Comments
Just acquiring the final hardware now, then fabrication, test, & video!
Well...Okay.
I thought Matt Gilliland was the only one allowed to post teaser threads.
PHEW. Am I off the hook temporarily?
I'd say you still have a lot of community service left on your sentence.
Are you talking about one of these? If so that's a great idea. (I have one, I might use it this way.)
If not it's probably still a great idea. I just don't know what you're talking about.
Duane
And I'm building a 13" diameter chassis as we speak. Plastic? Nah. Plyood? Yeah!
Edit: Can we pretend I didn't make such a dumb joke? Apparently by sense of humor has already gone to sleep. It's time for the rest of me to follow. I wish it weren't against my religion to delete posts or I'd delete this one.
1. The SoftPots aren't sealed, so be careful using them outdoors. They sell a HotPot line, which are sealed, but these require more pressure to actuate.
2. Very hard impacts will permanently damage the membrane. You'd be wise to put the strip within a recess so that it won't take the full force of hit.
3. It's not possible to read multiple contact points. It will register the nearest point only. (One way around this is to use a second strip, mounted in reverse direction. Then you can tell if there's at least two separate contact points. This is a pretty expensive route, though.)
I think they're fine as a failsafe for when proximity detection missed an object. Given a one meter strip, and assuming one loop around the robot's base, I'm guessing a one foot diameter bot. That's no bantam weight. With that kind of mass, given any speed at impact your SoftPot may not last long. So be gentle to it!
You might also consider putting some foam on the outside as a cushion. I don't know how that will affect its sensitivity, but it would probably help it to last longer in the Erco household.
-- Gordon
I'm not a huge fan of circular robots, but yes, this one will be 13" diameter to keep the bend as gentle as possible. And the plan is to have vinyl or surgical tubing all the way around for protection.
You guys are sharp!
Something that would expand the surface area of a bump vertically but not so much horizontally would probably benefit the SoftPot. The combination of the recess and the tube could help prevent the strip from the full force of the impact. As the tube compresses it spreads out to the recess, filling it, and preventing the object from going any deeper -- the object hits the ridges of the recess as a hard stop.
Maybe you could find an inner tube that's the right size. Steal the one from your kid's first bicycle, maybe. Fill it up to the pressure that still registers the bumps in more or less the right spots.
-- Gordon
I think large surgical rubber tubing will work well as a protective bumper.
How does a liner pot react if there are two points of contact? Does it act like resistors in parallel?
Or, just the same as the lowest resistance reading.
Whichever comes first.
@Ron: It's guaranteed to work at least until the first good impact.
The sensor just sends the lowest resistance?
edit: What happens when the surgical tubing contacts the sensor? it will have to be held off of the sensor, yes?
Anyways, looks like fun. Thanks for sharing..
Sounds like split one edge of the tube and attach only on the top side.?
At first I thought about expanding foam behind the sensor as a shock absorber,
but that does not help solve the "it can't touch the sensor face" part of the problem.
Easy enough to draw...
looks like it will take some very flexible and thin surgical tubing..
edit: Scratch the expanding foam, and think weatherstripping instead..
Hrmm, gonna have to think outside the circle for this. Can't wait to see what you come up with..