Wheel Problems

[ypang9804]

Hi all
I have been having trouble with wheel slip on my car. Currently, I use CD wheels (2 glued together) with balloons wrapped on them, but I have had severe issues with the wheels slipping when testing on the gym floor. I used a longer gearing for the car, but the wheel slip issue was still there at regionals on a linoleum floor. Also, I discovered the hard way that linoleum is much slicker than waxed hardwood, and had much more skid than I expected and would like. Does anyone have wheel recommendations or places to get wheels that have better grip than razor-thin plastic? I have looked at Banebots, but I am worried the hubs will slip off the axle without glue. Is the reduced grip of CDs really worth the possibly added weight of new wheels?

Note to moderators: I am new to the forums, so sorry if I am not supposed to post a question for Wheeled Vehicle in Scrambler. The Wheeled Vehicle forum is quite inactive.

[mnoga]

First, recognize that you cannot eliminate all wheel slip, and as you found out it varies from floor to floor depending upon the floor's coefficient of friction and its smoothness. Wheel slip also depends upon launch speed and tends to decrease as a vehicle slows down. In this discussion I'm talking in general about the various SCIOLY vehicle events, e.g., gravity vehicle, electric vehicle, scrambler, mousetrap vehicle.

If you can't eliminate wheel slip, then the best you can hope for is consistent wheel slip, and that is usually achieved by quality wheels, axels, hubs, and bearings. Generally the goal in your wheel configuration is to eliminate as much wheel-wobble as possible and to keep your front and rear wheel pairs as balanced as possible.

We have used various websites to find our wheels, hubs, bearings, and axels/threaded rods including Banebots, Servo City, Pololu, McMaster-Carr, and RC Planet. Depending upon the event, you need different diameters, weights, widths, and grip characteristics for your wheels. Generally there is no right answer for any event, but usually there is a range of what will work well. For example, you would not use a heavy or large diameter wheel for mousetrap vehicle, but for gravity vehicle this approach might be ok.

Practicing with your vehicle and launching devices on both wood and tile floors is always a good idea as it allows you to gather enough data to create reference spreadsheets that can be used in actual competitions.

[pumptato-cat]

I used Banebots for Mousetrap last year, and they completely eliminated skid, but my vehicle became very slow and heavy. Also note that it did not skid because of slow speed. I'm not sure how they'd fare with WV speeds.
The hubs never came off. They are attached by metal hubs with holes in them for friction-fit screws. If you'd like further explanation, feel free to PM. I can send pictures of the Banebots I have. Again, not sure how they'll do with WV but if your car isn't going very fast you should be fine.
Do you have access to a 3D printer? I printed some wheels and used rubber bands on them--they work quite well. No skid at all, but my brakes are consistently 6-7cm off. A small offset works wonders and good accuracy is possible. Like mnoga said, if you keep good logs and take slow-motion videos to watch for skid, you should be fine(assuming your skid is consistent after switching wheels). If the skid is still bad, consider slowing down your car. Accuracy is almost always worth more than time.
Oh, I almost forgot to mention this. Do you clean your wheels? If you don't, balloons(and rubber bands) get dirty fast and will give bad traction. Cleaning with alcohol wipes(or in extreme cases, switching balloons) between every couple runs works great. Cleaning the track if you're practicing in a dirty floor is also helpful(yes, I have actually brought Swiffers with me to practice!).
Also, Wheeled Vehicle would be the correct place to ask questions. It depends on what the mods say in the end. Questions about wheels apply to all vehicle events so I don't think it matters much where you ask

[poonda]

i personally think that cd wheels are just not that great to use; id invest in other wheels
banebots should work fine. don't worry too much about weight: since there arent any restrictions on power for wv this year, you can just add more power if you want your vehicle to go faster.
also i second everything pumptato said

[sneepity]

First, recognize that you cannot eliminate all wheel slip, and as you found out it varies from floor to floor depending upon the floor's coefficient of friction and its smoothness. Wheel slip also depends upon launch speed and tends to decrease as a vehicle slows down. In this discussion I'm talking in general about the various SCIOLY vehicle events, e.g., gravity vehicle, electric vehicle, scrambler, mousetrap vehicle.

If you can't eliminate wheel slip, then the best you can hope for is consistent wheel slip, and that is usually achieved by quality wheels, axels, hubs, and bearings. Generally the goal in your wheel configuration is to eliminate as much wheel-wobble as possible and to keep your front and rear wheel pairs as balanced as possible.

We have used various websites to find our wheels, hubs, bearings, and axels/threaded rods including Banebots, Servo City, Pololu, McMaster-Carr, and RC Planet. Depending upon the event, you need different diameters, weights, widths, and grip characteristics for your wheels. Generally there is no right answer for any event, but usually there is a range of what will work well. For example, you would not use a heavy or large diameter wheel for mousetrap vehicle, but for gravity vehicle this approach might be ok.

Practicing with your vehicle and launching devices on both wood and tile floors is always a good idea as it allows you to gather enough data to create reference spreadsheets that can be used in actual competitions.

Consistent wheel slip is really hard to determine, as variations in launching power or even relatively small changes in the weight of the car will change how much the car skids. The skid is also variable depending on the floor material and the amount of dust on it too! The best solution is to add mass on your braking axle and dry out your rubber tires by buffing it. But those are small fixes, if you have a huge skid issue, then you will have to find new wheels or estimate skid inaccurately :o (

[pumptato-cat]

Consistent wheel skid isn't impossible if the car is moving at a slow speed. It's definitely possible to completely eliminate skid. I was able to do that for MTV last year(speed did not matter) and accuracy got to sub 2 consistently.

[ypang9804]

Thanks for all the suggestions! Currently, my car travels at 1.8 m/s, give or take, so skid is an issue. The car has quite a bit of skid, albeit somewhat consistent. I usually will have the car set to brake 2 m early to account for it. It is still a good 30 cm off, but usually due to the fact that the car is not angled correctly (the car wounds up left or right of the aiming point despite traveling mostly straight). I will work on aiming it better with my partner to improve accuracy. I probably will go with Banebots right now, and look into 3D-printed wheels. I know my school's Division C team is using 3D wheels, so I do plan on talking to them.

On cleaning the track, how much of a benefit will this provide? Is dust buildup really that bad? I usually had to replace balloons on my car fairly often as I would break them either putting them on the car or they get torn up, so I haven't had that much experience with particularly dirty balloons.

[sneepity]

Thanks for all the suggestions! Currently, my car travels at 1.8 m/s, give or take, so skid is an issue. The car has quite a bit of skid, albeit somewhat consistent. I usually will have the car set to brake 2 m early to account for it. It is still a good 30 cm off, but usually due to the fact that the car is not angled correctly (the car wounds up left or right of the aiming point despite traveling mostly straight). I will work on aiming it better with my partner to improve accuracy. I probably will go with Banebots right now, and look into 3D-printed wheels. I know my school's Division C team is using 3D wheels, so I do plan on talking to them.

On cleaning the track, how much of a benefit will this provide? Is dust buildup really that bad? I usually had to replace balloons on my car fairly often as I would break them either putting them on the car or they get torn up, so I haven't had that much experience with particularly dirty balloons.

I believe pumptato probably had very small amounts of skid with her MTV, due to her speed being very slow. But since speed is a factor this year, it's important I think to preserve the speed you have right now! If your car is travelling at 1.8 m/s, is it closing the 7 meter distance in about 4 seconds? I can def see how skid is an issue at that speed! Even though the skid might be semi-consistent for now, it's not very reliable in determining how to set your brakes (especially since you want to aim for close distances!!). Setting the car to brake early for 2 meters is huge, ideally you would only want to set your brake early maybe 15-20 cm. Car angling is also a huge problem I had and you should look in the other posts made this year about scrambler, there's some suggestions to correct for straightness. Banebots will slow down your car an extreme amount (I'd say 6-8 seconds instead of 4). Try to 3d print wheels as soon as possible! Another suggestion is to try adding weight onto the cds themselves and near the axles too, but cds are still not as great as other wheels.


Dust buildup doesn't make a huge difference when you have heavy grippy wheels like banebots, but for very thin and light wheels, it does make a slight differenc. It's just a variable that we don't like to take into consideration, but could be a small fix when you're having very little skid. I don't think it's required to take into consideration just yet tho!

Also: wanted to clarify, consistent wheel skid is hard to determine for light, fast vehicles, as the lighter you get, the less stability you have in your car overall. If you keep the quality of your build good, and your launcher as an unchanged variable, the skid distance is easier to determine. But rarely in practice do all variables remain constant

[pumptato-cat]

Sneepity, I think this person's referring to WV, not Scrambler. You're definitely correct about not worrying about cleaning the floor just yet--it shouldn't be a concern until you're under 10cm accuracy, but in extreme cases, may cause skidding or slow the car down.
After skimming WV rules, I strongly recommend that you slow your car down by quite a bit. What is the weight? Time is only worth twice as much as distance(so think of it this way: 1 second adds the same amount as 2 cm to your score), so currently, your accuracy is increasing your score more than time. I'd focus on getting <10cm accuracy before I even consider speeding the car up. Banebots might work well. I'd strongly recommend you 3D print wheels-I use rubber bands as my treads and they work almost as good as Banebots, at higher speeds, too!