Why such large wheels?
 

Why do teams use such large wheels? Especially when they still make their ground clearance so low. It takes more space, weight, and gearing. If your wheels are large, do you have a good reason?

Re: Why such large wheels?
 

What do you consider large?

We typically use 6" or 8" wheels mostly because we bought a lot of them and they are in the shop. This year we went to 4" for our design because they were the right choice for our design.

Re: Why such large wheels?
 

8in
they come with the kit

if done right big wheels can look really cool, not in a "spinners and chrome" way but kind of a tuff look

Re: Why such large wheels?
 

We're using 8" kit wheels not because of a desire for big wheels, but because we have seventeen cents in our team account (and a new drivetrain head). (but a budget of $1000... interesting math) Anyway, my point is, the bigger wheeled teams might do it for budget, or happen to have them lying around. Or, they could want a solution to speeding up their robot without gears. In previous years we used bigger wheels because we had had sucess with them. As a matter of fact or '03-'05 robots used the same wheels with minor tread pattern differences.

Re: Why such large wheels?
 

Well i think the concept is that they will have more surface contact with a wider radius of wheel. In practice, I'm not sure if this works. We went with about 6" diameter, 1.5" wide wheels and they gave us enough traction to push around whoever we wanted (except two teams, sadly)

Re: Why such large wheels?
 

We went with 8" wheels for the reason you first stated; we need the clearance.

Had it been a different game, I would have wanted to go with smaller wheels, maybe 4". This leaves more room for other things on the robot chassis, and there really isn't any reason I can think of to use larger wheels if you don't need to clear a ramp.

Re: Why such large wheels?
 

bigger wheels=less rpms. so the bearings dont take as much abuse when its not a perfectly straight axle. and also a larger sprocket can be mounted.. in general a larger sprocket is harder to derail chains from.

Re: Why such large wheels?
 

This year, 1293 is going with 8" Skyways on the outer four wheels, and IFI wheels in the middle of our 6WD setup. A big reason for this is cost and lack of need--six roughtopped wheels from IFI, doubled for a practice robot, would be quite expensive. Since we seem to be driving around just fine with our current arrangement, with no noticeable wheelspin even on our slick tile floor, we're sticking with it.

On a side note, these are actually the lightest wheels we've ever used on a robot. On Bob, we used the 12.5" pneumatic Skyways that came in the kit. Last year, we had these big heavy 8"x2" wheels that, ignoring cockroaches, would be the only things to survive a nuclear blast. Staying with lighter wheels this year is a change for us, but I think it's definitely working for the better.

Re: Why such large wheels?
 

team 25 uses 9x3 skyway wheels, why? cause it works for us we swear by them

team 1923 is using 6 8in skyways 2 in the front and 4 in the back again why? cause it worked for them

its all a matter of taste

Re: Why such large wheels?
 

Why such small wheels?

Ours are 8.5'' in Diameter, who can guess what kind of traction material we have?

Re: Why such large wheels?
 

This is our third year. Each year we have used smaller wheels. Our first ones were monster 12" x 2" pneumatics in a 4x4 arrangment. That was done so we could climb up the 6" step.

Last year we used 8" wheels in a 4x4 arrangement with pneumatically actuated caster wheels to help with turning. That was done so we could drive over the bottom edge of the goals if we needed to (as it turned out, it would have been better if we couldn't).

This year we are down to 6"x1.5" wheels in a 6x6 arrangment.... just enough to get up the ramp.

There are many advantages to the smaller wheels, namely reduced weight and size, but also that because the radius is reduced you can put the contact point of the wheel closer to the outside of the robot, thus improving your front/back stability. The bigger wheels are better for climbing over obstacles and for ground clearance. The big wheels from our first year also gave the robot a very rugged "Moon Buggy" type look. Aesthetically it is still my favorite of our three robots, but, well... it didn't really perform all that well.

Next year we are just going to put a few skyhooks on and let it hover.

Jason

Re: Why such large wheels?
 

We believe 3.375" is just enough to get up.

Re: Why such large wheels?
 

After seeing the regionals, I think it's time to revisit this.

Why are all your wheels so big? We get up the ramp just fine with 1 inch wide 3.3" diamter wheels (6 of them) and 3/4" of ground clearance under our side frame rails and about 3/16" clearance under our gearboxes.

Your wheels do not need to be big. Your ground clearance does not need to be high. You are causing more trouble for yourselves. I'm sure in some cases, there is a darn good reason for it that the team thought very hard about, but in most cases I've seen, I ask and they say "oh, smaller wheels, hrrm, never thought of that"

Re: Why such large wheels?
 

We use 12 inch pnuematic wheels - 3 per side. The reason is three fold - they are grippy for climbing, a completed purchased assembly that we have little work to do to modify for use, and best of all they cost about $7 per wheel including the bearing.

We used them over the past 4 years, and have gotten used to them and like them alot.

Re: Why such large wheels?
 

Finding wheel/tire combinations with the right width is what drives our selection process. Since we went to two wheel drive for control issues, we also can go for maximum traction, hence very wide wheels.

Re: Why such large wheels?
 

Lets see... as I've mentioned in an earlier post, we used the six of the 8" KOP wheels (with SBR Roughtop conveyor belting on them) for budget reasons. They worked extremely well, we never came close to tipping, we got insane traction (although we did leave some rubber on the carpet during our more "spirited" pushing matches), and our ramp climbing was among the smoothest at VCU. (We didn't have to charge it or anything, just drove up it normally) For many cases it shouldn't really matter much, if your center of gravity is high enough that you need smaller wheels, then you have bigger problems. That said, I happen to think that those little wheels on 696's machine look really stylin' and am looking into Colson wheels for our drivetrain next year. (There are other reasons why small wheels will be desirable in a couple of the many drive configurations I'm looking into)

Re: Why such large wheels?
 

We use 6" skyways turned down to 5" and rivet on wedgetop belting. So.. we use six 5.5" wheels. Sanddrag has a point, you dont need very big wheels to get up the ramp. We used skyways because they're like, 5 bucks each, have precision bearings, weigh next to nothing, etc. So our team bought twenty. We have 1" of clearance below the chassis, but we get up the ramp smooth. We have strategically placed rollers on the underside of our chassis, so we never beach.

I say, the bigger the wheel, the harder it is to fit and the harder it is to get a reduction that big. However, the smaller the wheel, the more your tread dies because there is less of it. I think 5-6" wheels is the perfect balance for what my team needs.

Re: Why such large wheels?
 

In our configurations 2.75 was enough cuz the front of the wheel hit the ramp on the slope before the frame bottomed out, however since then we've raised it for other reasons ( namely ball intake and jumping problems )

Also some teams using old robots with .5" clearance getting up, its just not very consistant from what I understand unfortunately.

We used the 8" wheels for clearance and they've worked great.

Re: Why such large wheels?
 

We use 6 8" wheels. The front and back set of wheels are 1" wide and the center wheels are 2" wide because they will always be on the ground.

We use 8" wheels because we need clearance for the the ball to travel under our robot and to our harvester.

Re: Why such large wheels?
 

My team initially had a tank tread design. It was optimal we figured because we could keep ourselves very low to the ground and easily get up the ramp. We had about 3/8" to 5/8" inches of clearance on our chassis depending on where you measured. However at our first regional this year our treads all sheared so we were forced to convert our robot into a 2WD set up. We wrapped the tread around the one driven pulley and put some smooth material on the front pulley. We just assumed at this point that the ramp was out of the question. However in one of our matches an opposing team gingerly pushed us up their ramp and plopped us on the top of their ramp. It got us thinking and we took our robot over to the practice field. Turns out with 2WD and less than half an inch of ground clearance we can still scrape our way onto the top of the ramp. Its not pleasant and once we peak at the top our drive wheels hang in the air, but its far from unreasonable and its perfect for last second ramp point scoring. So onc can get up with basically no clearance that means. We still have about 6" wheels but thats just due to the nature of the tank tread drive train. At our regional next week we're going to modify the drivetrain again to either a 4WD or possibly a 6WD set up. 4WD won't help us get up the ramp, but a 6WD set up would make it even easier. Our other idea is put delrin or HDPE slides on the bottom of the chassis to make it glide more easily over the top.

Re: Why such large wheels?
 

We have always used 8in. wheels and they have always worked for use. One thing though is you stated that larger wheels will take up space. this in a way kind of puzzling. how many times have you ever put something near your wheels? personally through previous experiences we try to avoid putting anything near a moving object, especially a wheel (except chains, axles, etc..). also design comes into consideration. maybe you need x amount of clearance and those 8in. wheels are looking like the easiest way to get to that Clearance. anyways everyone has there own considerations so some times it just happens that you have to use those big wheels. in the future your team might even consider to use large wheels for similar issue or facts. anyways have a great year at comp. and good luck.

Re: Why such large wheels?
 

Your clearance over the ramp will depend greatly on your wheel placement, not only the size of your wheels. Robots who have their wheels placed near the edges of the 38" space will need greater ground clearance than those who are mounted further inwards. The reasoning to space them further out being a more stable drive base in terms of center of mass while climbing the ramp (although less stable if taking impacts from the sides). Additionally it matters how your wheels are mounted to your frame (how far beyond the bottom they extend, as it really isn't the size of the wheel that matters, it the ground clearance, and the two factors are not the same).
Additionally, the relationship between ground clearance and wheel size is altered by the number of wheels you have (as this will change the contact points as you travel up the ramp).
Also, as mentioned before, a larger wheel results in less rpm on the drive shaft to acheive the same speed, which in turn means less stress on the bearings.

Re: Why such large wheels?
 

Big wheels are pimp.

We've been doing 8 inch wheels for years and it works for us.

Re: Why such large wheels?
 

One word...

Preference.

Re: Why such large wheels?
 

6 inch wheels are what we have gone with for the last 2 years. We like them because they allow for climbing easily, and are generally nice to design into as frame. As for what we use for the wheels, we had our own made by our CNC sponsor. you can see them here: (http://www.chiefdelphi.com/media/photos/22758)

One of the main reasons we pick this size over others is the fact that we've used it many times before, and it has been reliable and consistent. We perfer to stick with something we know works, and only go out on a limb for a new design occasionally.