Sharp Wheels

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Posted by Josh Vetter at 1/23/2001 12:04 PM EST


Student on team #548, Robostangs, from Northville High School and BOSCH.



I am on a rookie team this year, and we are trying to provide our robot with more traction to pull the goals onto the bridge. In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?
Any other ideas to get more traction would be appreciated too!

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Posted by Joe Ross at 1/23/2001 12:20 PM EST


Engineer on team #330, Beach Bot, from Hope Chapel Academy and NASA/JPL , J&F Machine, and Raytheon.


In Reply to: Sharp Wheels
Posted by Josh Vetter on 1/23/2001 12:04 PM EST:



: In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?

My initial reaction was that FIRST would probably DQ you if you used something like gears for wheels, but then I remembered a team (308) last year did use gears for wheels. See the picture below. Basically you would need to test it and see if it damages the carpet. I don't think FIRST would DQ you just for using gears, but they will definetly test to see if they damage the carpet.

: Any other ideas to get more traction would be appreciated too!

There have been to recent discussions that I can remember about what you can do to gain traction.

http://www.chiefdelphi.com/wwwboard/messages/.2001/1932.html
http://www.chiefdelphi.com/wwwboard/messages/.2001/1023.html

I hope this helps and good luck on your design.

Joe Ross
Beach Bot, Team 330

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Posted by Anton Abaya at 1/23/2001 12:45 PM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.


In Reply to: Re: Sharp Wheels
Posted by Joe Ross on 1/23/2001 12:20 PM EST:



: : In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?

: My initial reaction was that FIRST would probably DQ you if you used something like gears for wheels, but then I remembered a team (308) last year did use gears for wheels. See the picture below. Basically you would need to test it and see if it damages the carpet. I don't think FIRST would DQ you just for using gears, but they will definetly test to see if they damage the carpet.

: : Any other ideas to get more traction would be appreciated too!

: There have been to recent discussions that I can remember about what you can do to gain traction.

: http://www.chiefdelphi.com/wwwboard/messages/.2001/1932.html
: http://www.chiefdelphi.com/wwwboard/messages/.2001/1023.html

: I hope this helps and good luck on your design.

: Joe Ross
: Beach Bot, Team 330


we almost did this idea for a wheel this year and it may be of interest to you.

the plan was to get the biggest sprockets we could get (60 teeth) and mount some angle aluminum around the wheel and putting some kind of rubber material (found in small parts) on them to make contact with the carpet. With this idea, we eliminated the need for hubs and just chained the sprockets which doubled as our wheel.

-anton

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Posted by Michael Betts at 1/23/2001 1:03 PM EST


Engineer on team #177, Bobcat Robotics, from South Windsor High School and International Fuel Cells.


In Reply to: Re: Sharp Wheels
Posted by Joe Ross on 1/23/2001 12:20 PM EST:



Josh,

Joe's comments to you are correct. Two things to keep in mind...

Go to your contest with a couple sets of wheels which have varying degrees of "aggressiveness" in their design. Trying to appease a finicky inspector in the pits is the pits.

Another thing to keep in mind is that the FIRST "criteria" will vary from contest to contest. I have had designs approved at one regional and disallowed at another regional a week later.

It's best to adopt the U.S. Coast Guard's motto in these matters: Semper Paratus

Always Ready (for those of you who did not study Latin).

Mike

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Posted by Rob DeCotiis at 1/23/2001 5:32 PM EST


Student on team #504, RoBUCtics, from Red Bank Regional High School and Jesel.


In Reply to: Re: Sharp Wheels
Posted by Michael Betts on 1/23/2001 1:03 PM EST:



boy scout motto... be prepared... definitely have different types of wheels at the regionals

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Posted by Justin Stiltner at 1/23/2001 8:14 PM EST


Student on team #388, Epsilon, from Grundy High School and NASA, American Electric Power, Town of Grundy.


In Reply to: also the boy scout motto, kinda...
Posted by Rob DeCotiis on 1/23/2001 5:32 PM EST:



: boy scout motto... be prepared... definitely have different types of wheels at the regionals

OK I need sombody to explain somthing to me
We want more traction so I tell our Engineer that we need wider wheels to put more area in contact with the ground. and he says no we would gain NOTHING out of it because the wheels would have less weight on each square inch. But the way I am thinking is that we will not find a materal that has a high enough Friction that it will stand up to the sheer force when only about 1 square inch of it is in contact with the carpet. And if he is right then why do dragsters and high proformance cars have wide back tires. and I know from personal experance that a vehicle with skinny tires will spin before one with wide tires. (except in snow where you want to bite into it )

so could sombody tell me who is correct??

Justin Stiltner
Team #388
Epsilon
Grundy Va,

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Posted by Matt Berube at 1/24/2001 8:19 AM EST


Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.


In Reply to: Re: also the boy scout motto, kinda...
Posted by Justin Stiltner on 1/23/2001 8:14 PM EST:



Your engineer is correct, technicaly.

The reason cars get more traction with wider tires is because the tire material is so compliant. If you were to ignore the effect of the tires sidewall and ignore the deflection of the tire under torque then the car would get the same amount of traction with skinny tires or fat tires. It doesn't because the tire patch size increases as the tire deflects under torque.

I assume that your robot tires will not be deflecting under torque. However, the carpet does deflect some wich causes the robot wheels to behave somewhat different than the classical physics model.

I guess my long winded suggestion is to make a couple model wheels and put the same weight on both then pull them across a carpet with a string and a hard scale so you can measure the traction force.

Hope this helps.
Matt B.
T49

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Posted by Jim Meyer at 1/24/2001 8:44 AM EST


Engineer on team #67, HOT Team, from Huron Valley Schools and GM Milford Proving Ground.


In Reply to: Re: also the boy scout motto, kinda...
Posted by Justin Stiltner on 1/23/2001 8:14 PM EST:



: OK I need sombody to explain somthing to me
: We want more traction so I tell our Engineer that we need wider wheels to put more area in contact with the ground. and he says no we would gain NOTHING out of it because the wheels would have less weight on each square inch.

I suggest that you should do some experimentation. Friction is not neccessarily a very intuitive thing, especially when you are working with carpet. I suggest trying lots of stuff.

On the wheel width thing we have found that some materials develop more traction with wider wheels, but some do not. If you want to demonstrate this to your engineer I suggest using the toothed side of some timing belt. (Tracked vehicles that use doublesided timing belt develop lots of traction.) If you are interested in how to set up a friction test, I would be more than happy to elaborate.

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Posted by Dave at 1/23/2001 2:02 PM EST


Other on team #308, Robo Stars, from Alumni from Walled Lake Western and TRW.


In Reply to: Re: Sharp Wheels
Posted by Joe Ross on 1/23/2001 12:20 PM EST:



As being from Team 308 last year, I'll comment really quick on the wheels. They started out as circular disks, and we machined out the groves, leaving us with teath. I can't remember all the specifics on them, but they didn't come to a point. They still had lots of traction since the edge of each tooth was pretty sharp, and we didn't tear up the carpet at all.

Dave Hurt
dmhurt@mtu.edu


: : In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?

: My initial reaction was that FIRST would probably DQ you if you used something like gears for wheels, but then I remembered a team (308) last year did use gears for wheels. See the picture below. Basically you would need to test it and see if it damages the carpet. I don't think FIRST would DQ you just for using gears, but they will definetly test to see if they damage the carpet.

: : Any other ideas to get more traction would be appreciated too!

: There have been to recent discussions that I can remember about what you can do to gain traction.

: http://www.chiefdelphi.com/wwwboard/messages/.2001/1932.html
: http://www.chiefdelphi.com/wwwboard/messages/.2001/1023.html

: I hope this helps and good luck on your design.

: Joe Ross
: Beach Bot, Team 330

[archiver]

Posted by Ken Patton at 1/23/2001 10:06 PM EST


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.


In Reply to: Re: Sharp Wheels
Posted by Dave on 1/23/2001 2:02 PM EST:



Dave-

And as I recall, they didn't spin either, so they must have been pretty good for traction. In the semifinals at Ypsilanti, you guys broke a chain when we got into a pushing match.

How did the robot turn? (for those that don't remember them or can't tell from the picture, they had 4WD) The "gears" would also make for pretty rough scrubbing action, I would think...

How do you like MTU, Dave? Are you on team 221?

Ken
MTU '85

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Posted by Chris Hibner at 1/24/2001 8:50 AM EST


Coach on team #308, Walled Lake Monster, from Walled Lake Schools and TRW Automotive Electronics.


In Reply to: and they didn't spin...
Posted by Ken Patton on 1/23/2001 10:06 PM EST:



: How did the robot turn? (for those that don't remember them or can't tell from the picture, they had 4WD) The "gears" would also make for pretty rough scrubbing action, I would think...

The robot turned wonderfully. The scrubbing wasn't that bad. We round the side edges of the wheel with a sufficient radius so that the wheels slide fairly easily side-to-side.

-Chris

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Posted by Ken Leung at 1/23/2001 4:37 PM EST


Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.


In Reply to: Re: Sharp Wheels
Posted by Joe Ross on 1/23/2001 12:20 PM EST:



Remember that if you are using gears, it have to be from Small Parts this year. Not sure if they have big enough gears compare to what you want. But if so, they are probably going to save you a lot of machining.

As for making your own wheels out of metal, I would advice you to design the wheels so that they especially do not hurt the carpet in any way. Make sure no matter what happens, they do not damage the field. Think about the wheels doing different motion: spinning, twisting, sliding, or pushing against the ground because of heavy weight of the robot. Earlier discussion suggest using timing belt on the wheel. So you might want to explore the option to machine wheels that can fit two-sided timing belt on them, and gain more traction that way.

Another way I've seen many teams do is to cut slots out of the surface of wheelchair wheels. You probably want to do this on your wheelchair wheels anyways to get more traction from them...

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Posted by JVN at 1/23/2001 12:56 PM EST


Student on team #250, GE Dynamos - Capital District Robotics Team, from Shenendehowa High School and General Electric.


In Reply to: Sharp Wheels
Posted by Josh Vetter on 1/23/2001 12:04 PM EST:



: I am on a rookie team this year, and we are trying to provide our robot with more traction to pull the goals onto the bridge. In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?
: Any other ideas to get more traction would be appreciated too!

Well FIRST definitely won't DQ you if you build em. Last year in Long Island there was a robot like that. It got pretty decent traction, it even stood up to our gearboxes (we were tossin other bots around)

Good luck with it...

~John#250

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Posted by Chris Orimoto at 1/23/2001 5:59 PM EST


Student on team #368, Kika Mana, from McKinley High School and Nasa Ames/Hawaiian Electric/Weinberg Foundation.


In Reply to: Sharp Wheels
Posted by Josh Vetter on 1/23/2001 12:04 PM EST:



Well, as most of these people have been saying, as long as you don't damage the carpet in any way, then your machined wheels should be fine. To help a little, try to think of other materials that have a large coefficient of friction with carpet. Certain other teams last year filed grooves onto their skyway wheelchair wheels to add traction. But, all suggestions aside, I think you have a very good idea there.

Chris, #368

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Posted by Raul at 1/23/2001 6:59 PM EST


Engineer on team #111, Wildstang, from Rolling Meadows & Wheeling HS and Motorola.


In Reply to: Sharp Wheels
Posted by Josh Vetter on 1/23/2001 12:04 PM EST:



Consider the scenario where your robot is prevented from moving by an unmovable object such as a wall. But in our case, it will most likely be the robot trying to pull too much weight up a ramp (such as a stretcher with a robot on it).

From experiments and experience, the way I see it, your wheel design will lead to 1 of 3 things:

1) You get great traction; so much so that your wheels never spin freely and your motor stalls. That will either burn out your motor or trip a fuse.

2) Your wheels spin freely and they are made of a material that rips away. This happened to us quite often when we used the wheel chair wheels. We went through many spare wheels that year.

3) Your wheels spin freely and they are made of some hard material with sharp edges and thus they rip up the carpet. OR, they are made of a hard material with no sharp edges and you burn the fibers of the carpet.

We have experienced all three scenarios above. We usually settled on #2 or #1.

The most tempting solution is #1 using a wheel material that is either very sticky or digs in with sharp edges so your wheels never spin. BUT, you must gear your speed down so that you have enough torque to overcome any load condition under game conditions. This is more predictable this year because at least you do not have to get into a pushing match with other robots (at least I hope no one does).

However, be aware that if you do use sharp edges as a way to get great traction , FIRST will likely ask you to do the carpet test. I believe that means running your robot against a wall. So in that case you have to make sure that you have so much traction that it will just stall your motors. I think TKO had this configuration with their tank treads in 99.

Raul


: I am on a rookie team this year, and we are trying to provide our robot with more traction to pull the goals onto the bridge. In addidition to doing four-wheel drive, we are thinking of making some wheels out of metal, which would be similar to a gear, but with points. Would this be allowed, or would FIRST dq it because it could damage the carpet?
: Any other ideas to get more traction would be appreciated too!

[archiver]

Posted by Dodd Stacy at 1/23/2001 9:18 PM EST


Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.


In Reply to: 3 Choices - Hurt Carpet, Motors or Wheels
Posted by Raul on 1/23/2001 6:59 PM EST:




: However, be aware that if you do use sharp edges as a way to get great traction , FIRST will likely ask you to do the carpet test. I believe that means running your robot against a wall. So in that case you have to make sure that you have so much traction that it will just stall your motors. I think TKO had this configuration with their tank treads in 99.

: Raul

FWIW. In 98's Ladder Logic, we anticipated just this scenario. We machined little pyramid spikes, about 1/16" square at the base, on aluminum wheels and geared just tall enough to stall the motors up against the wall. The tech inspector took one look at our wheels and put us to the carpet test.

However - surprise - when he saw that we stalled, he lifted our wheels off the ground, let them spin up to free speed then lowered just enough weight back down on the carpet to load the wheels heavily (at full stick) but not quite stall the motors. Needless to say, you can burn the carpet with rubber Skyway tread with this test.

Fair? Legitimate? We didn't think so at the time, and I still think it was arbitrary and discriminatory. But I'm not posting to rant. I'm posting to warn inexperienced teams that this is a gray area, and the FIRST folks have a playing field to maintain. They are not obliged to take risks with us tearing it up, and they make the rules. Be prepared with conservative options if you want to push the traction envelope, or be prepared to trailer your bot without competing.

Dodd

PS We teched just behind TKO at one of the tournaments, and I think the only reason they made it was that the inspector couldn't figure out how to lift up a tracked vehicle.

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Posted by Ken Wilson at 1/24/2001 5:03 AM EST


Engineer on team #248, FEMEX, from Philadelphia Girls High and PECO Energy Company.


In Reply to: The Carpet Test
Posted by Dodd Stacy on 1/23/2001 9:18 PM EST:



: FWIW2 - At the Philly Alliance Double Trouble regional (CD was there, quite impressively), there was a bot (names withheld to protect the innocent) that had fluted aluminum ?lugs? fastened to roller chain for tractive means. The assy looked like and - more importantly - acted like chain saw chain. Not so successful attempts to climb the puck resulted in a spray of carpet shreds from the puck's upper periphery. That was apparently OK. Put another point in the "inconsistent or selective judicial application" column.

kenny

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Posted by Jason Iannuzzi at 1/24/2001 10:05 AM EST


Engineer on team #11, Marauders, from Mt. Olive HS. and BASF, Rame Hart, CCM.


In Reply to: Sharp Wheels
Posted by Josh Vetter on 1/23/2001 12:04 PM EST:



I think almost any wheel type would be OK, just make sure you have removed the sharp edges. If you use a gear, try running all the teeth through a wire wheel first, it will remove the burrs and significantly reduce carpet destruction.