How well does this work on carpet?

[NextPerception]

I saw this picture
http://www.firstroboticscanada.org/site/files/active/1/322_small.jpg

I am assuming those are just delrin skids and I was wondering how well these work on carpet. anyone know?

[Jeremiah Johnson]

I'm not sure how well that one worked, but I've seen others like that and they didn't really have any glaring problems. Could be pretty unstable and would easily get caught to the point of no return on the game field.

[NextPerception]

really. I am not worried about the actuating part on that robot just the skids. it would make our design much simpler to use skids instead of casters or omni wheels (we are considering the 2-wheel drive with casters set up)

[redbarron]

If you are asking if they serve as a good skid plate than yeah it works, but you wil not have much traction at all. You will be pushed around very easily, especially if it gets pushed from the side towards the front. Also, if you are planing on going up a ramp the odds wil be against you.

[ChuckDickerson]

I am not familar with that particular robot but I believe it must have been from 2004 and designed to retract those front legs to get up on the platforms. The biggest problem I see would be if the air cylinder rams got bent you would be screwed because you couldn't retract the legs. I would be very careful about just a simple rod like that with a skid on the end for this reason. As far as a slick Delrin, etc. skid I think many teams have used them successfully over the years on the carpet.

[redbarron]

Why are you looking at casters or skids?

[NextPerception]

it shouldnt be any harder to push one with skid plates and a two wheel drive setup than one with a two wheel drive with omnis or casters correct?

[redbarron]

No I would think they were all in the same general category when it comes to resistance when being pushed, but why are you avoiding wheels?

[MrForbes]

If it has to go up a ramp, just make sure the skid pads have a large enough radius that they will go over the edge of most ramps without getting stuck.

[NextPerception]

No I would think they were all in the same general category when it comes to resistance when being pushed, but why are you avoiding wheels?

It would just be lighter weight and easier to implement (i could put it in a tighter ground clearence) than casters or omnis. I'm not avoiding wheels but if there is a better solution then I am going to take it .

If it has to go up a ramp, just make sure the skid pads have a large enough radius that they will go over the edge of most ramps without getting stuck.

im not worried about ramps...

[MrForbes]

im not worried about ramps...

yeah, I suppose if you're building the ramp, you don't need to worry about getting up on other ramps :)

[NextPerception]

yeah, I suppose if you're building the ramp, you don't need to worry about getting up on other ramps :)

tisk tisk squirrel.
that my friend is thinking inside the box

[redbarron]

Well I have seen these skid plates in action and they serve their purpose the only downside is that they have no traction. But are you going to be strictly a offensive robot?

[NextPerception]

Well I have seen these skid plates in action and they serve their purpose the only downside is that they have no traction. But are you going to be strictly a offensive robot?

"im not allowed to say" says matt as he nods his head up and down

atleast that is the plan right now

[redbarron]

Ok:D , Well, I would come up with something that is going to give you a little traction whether it be something you can activate or something that is permanent because if you are going to be an offensive bot this year I think you are going to be messed with a lot by defensive bots during the matches. Well good luck!! What events are you guys attending?

[NextPerception]

Ok:D , Well, I would come up with something that is going to give you a little traction whether it be something you can activate or something that is permanent because if you are going to be an offensive bot this year I think you are going to be messed with a lot by defensive bots during the matches. Well good luck!! What events are you guys attending?

well usually if you have enough torque (and enough motors) on your two wheel drive coupled to a gyro you can program it in a way to compensate for any outside forces. we have used the two wheel drive platform many times before and what it lacks in stability it makes up for in simplicity and weight.

Lonestar regional

[MattB703]

If you increase the torque to your wheels as you say, you will quickly hit the point where you are traction limited. Assume that we are all working with the same coeficient (sp) of friction on the carpet and that all the bots are at the same weight, a robot that has all of it's weight on driven wheels will out-push a robot that has caster/skids.

[NextPerception]

If you increase the torque to your wheels as you say, you will quickly hit the point where you are traction limited. Assume that we are all working with the same coeficient (sp) of friction on the carpet and that all the bots are at the same weight, a robot that has all of it's weight on driven wheels will out-push a robot that has caster/skids.

well of course this is going to be true but isnt it also true (correct me if i am wrong, i might be) that when trying to turn with a four wheel drive robot it is not as smooth and quick as when turning as a 2 wheel drive robot. therefore you lose time and it is really hard to get accurate position measurements from your encoders

[GeoffP]

I like the glides. it is likely just UHMW(PE). On carpet it will wear approximately 1/4" per hour of drive time. it may also get metal shavings imbedded and such imbedded in it from being moved around in the pit -- this will cause friction issues. I've considered the same but have not implemented to date. One nice thing about a static glide is that it will not get wrapped up in a deflated tube on the field like a caser will.

[Al Skierkiewicz]

Matt,
The rules that come into play here are 1) will there be any chance that this would allow metal to come into contact with the floor? 2) will it cause any damage to the carpet.
I think you will find that driving will cause this setup to heat considerably from the friction with the carpet. If the answer to either of the questions above is yes, it will not be allowed. The first is an inspection issue reguiring a close up look at construction and implementation. The second is to be determined by field people. If they think any damage is possible, they may disable your robot and disqualification for repeated offenses is a real consideration for your team. Without close inspection, only you can make a determination at this point.

[NextPerception]

Matt,
The rules that come into play here are 1) will there be any chance that this would allow metal to come into contact with the floor? 2) will it cause any damage to the carpet.
I think you will find that driving will cause this setup to heat considerably from the friction with the carpet. If the answer to either of the questions above is yes, it will not be allowed. The first is an inspection issue reguiring a close up look at construction and implementation. The second is to be determined by field people. If they think any damage is possible, they may disable your robot and disqualification for repeated offenses is a real consideration for your team. Without close inspection, only you can make a determination at this point.

I don't understand how either of these things could happen as long as a little bit of care is taken in the pits (aka replacing the slides after they wear down to a certain level or when they get metal shavings in them).

[Lil' Lavery]

yeah, I suppose if you're building the ramp, you don't need to worry about getting up on other ramps :)

Wait 'til the match all 3 teams on an alliance have that mentality... ;)



As for the delrin skids, several teams have used them in the past with success (success being in that they could move and control their robot accurately, not always actually winning matches). That being said, depending on your design, they may or may not offer any advantages or disadvantages over casters or dead omnis.
I know 422 has used skids several times, including 2003, 2004, and 2006 (probably 2005 as well, but I'm not positive). Here's a picture of their 2006 bot (which could make it up the ramp):
http://www.team422.com/robots/images/2006bot_l.jpg

[Rickertsen2]

Our second year, we had a system with two wheels and two skids like the one in the pic. It had trouble turning and was far too easy to push around. I would highly discourage this configuration.

If however you have two wheels in the middle and 4 skids at each corner of the bot, you have a highly maneuverable bot. We have tried this config with great success. It still suffers from the problem of being easy to rotate but it never presented a problem for us. If you are looking for a 2wd setup i think this would be the way to go. One thing to keep in mind with this config is that the skids must be a elevated a small distance from the height of the wheels. because of this the bot may rock slightly but it is usually negligible. This might not be a good setup for this year because it cannot climb obstacles but it is something to keep in mind.

I think the best overall combination for this yer would be simple 4wd.

[Al Skierkiewicz]

I don't understand how either of these things could happen as long as a little bit of care is taken in the pits (aka replacing the slides after they wear down to a certain level or when they get metal shavings in them).

Matt,
Just speaking from experience.

[NextPerception]

Matt,
Just speaking from experience.

I always apreciate anyones input that anyone is willing to give it
:)

out of those who have tried it, is it noticably easier or harder to rotate a delrin skid 2 wheel drive robot vs. a caster 2 wheel drive robot?

[redbarron]

Though I have no personal experience in the skid area I have driven a robot with casters, and I would say that the two wheel drive setup will not only lack in traction but it will tend to over steer until you practice with the bot a little bit. As far as wheels losing you time while turning, they will not with the right setup. If you have a bot that is wider than it is long than you will not have that problem. On th other hand if your designed bot is longer than it is wide it will tend to "jump" while turning, which is why it is popular for long bots to have > 4 wheels.

[NextPerception]

Though I have no personal experience in the skid area I have driven a robot with casters, and I would say that the two wheel drive setup will not only lack in traction but it will tend to over steer until you practice with the bot a little bit. As far as wheels losing you time while turning, they will not with the right setup. If you have a bot that is wider than it is long than you will not have that problem. On th other hand if your designed bot is longer than it is wide it will tend to "jump" while turning, which is why it is popular for long bots to have > 4 wheels.

wow, this makes a lot of sense now that you said that. does anyone know how to make a robot with theoretical values of, oh i dunno, 21.5 inches between the centers of the front and back wheels and 22 inches between the left and right wheels more stable as a four wheel drive robot (aka no bouncing). i know different types of wheels will matter but is it the coefficient of friction that is important. I know that what we do on our battlebot is use wheels that wear down when lateral force is applied and that is why it stays planted to the floor when doing turns on its 4 wheel drive but thats the only experience i have with 4 wheel drive

[Kyveck]

This is only my teams experience, but we used a drive train with two wheels in the center and four delrin skids on the corners in 2005. I don't have any pictures of the drive train though. The chassis was about 1//2" off of the ground in the center and the skids were raised 1/4". Initially we didn't do that, and had some trouble turning consistenty. It was definately a little difficult to learn to drive becuase it overshot turns so easily, but with a little practice and a lot of feedback control, our driver was able to control it very well.

As you would imagine, whenever we were bumped on a corner, we spun, but this wasn't as much of a disadvantage as we thought it would be. Our drivetrain was so maneuverable that we found it much easier to avoid the other robots, or just get out of the way. If we were bumped and couldn't move, we only spun, and we could spin back into position very quickly.

We replaced the delrin skids whenever they began so show strain or crack marks, about every 5 or six matches. They were very reliable, although they took a lot of time to form carefully with files and a dremel.

In 2006, we mistakenly tried the same drivetrain again, hoping to use powered wheels in the front which were usually off the ground to go up the ramp. The design, like most of our 2006 robot, was a flop. This drive base is inherently bad at ramps. We're trying something new this year, since we still want to be able to go up ramps.

Hope this might be helpful, and if you have any questions, I'd be glad to answer.

Kyle W,
Team 1014

[slickguy2007]

Matt,

Team 1403 used plastic sliders in 2004, and I don't recall having any issues with them. You are considerably more maneuverable, but do realize that you will be very easy to push when on the field. You will have slightly less control over the robot, and the driver will have to become used to the changes.

Make sure you have some extra sliders when at the competition because make no mistake, they will wear down. It's always good to have spares. :)