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OldSpice wrote:To agree with Balsa, CDs aren't the best choice for this event. If your team isn't overly competitive, roller blade wheels would probably provide a better balance between speed, stability, and accurate and precise braking.

If you go with the roller blade wheels, do all of them already come with their own ball bearings?

questionguy wrote:

OldSpice wrote:To agree with Balsa, CDs aren't the best choice for this event. If your team isn't overly competitive, roller blade wheels would probably provide a better balance between speed, stability, and accurate and precise braking.

If you go with the roller blade wheels, do all of them already come with their own ball bearings?

They should, but if you buy them from a store they might not. However, you can change/add bearings if necessary.

The effects on braking are going to be limited to minimizing the amount of slop/play in your axles. With ball bearings, the ability of either end of the axles to move under braking loads is going to be very small. With ‘washers and bolts’ its going to be significantly more. If you set them up to be nice and tight (minimizing slop), then the friction gos way up; if you set them up looser to minimize friction, then slop goes up. Axle movement will cause direction changes (not good). Where ball bearings are going to have a major effect (compared to ‘washers and bolts’) is before your brakes come into play -in your time score; significantly more rolling friction means vehicle momentum gets gobbled up faster; means vehicle slows down faster, means it takes more time to get to a given distance.

I doubt I understand this correctly, but are you saying that bearings will 'eat up' the momentum and increase your time score?

The effects on braking are going to be limited to minimizing the amount of slop/play in your axles. With ball bearings, the ability of either end of the axles to move under braking loads is going to be very small. With ‘washers and bolts’ its going to be significantly more. If you set them up to be nice and tight (minimizing slop), then the friction gos way up; if you set them up looser to minimize friction, then slop goes up. Axle movement will cause direction changes (not good). Where ball bearings are going to have a major effect (compared to ‘washers and bolts’) is before your brakes come into play -in your time score; significantly more rolling friction means vehicle momentum gets gobbled up faster; means vehicle slows down faster, means it takes more time to get to a given distance.

I doubt I understand this correctly, but are you saying that bearings will 'eat up' the momentum and increase your time score?[/quote]

I'm saying that ball bearings will "eat up" momentum at a slower rate than less efficient bearings (bearings with more inherent friction)- the vehicle will not slow down as fast, therefore the time score will be better. Reducing rolling friction = faster = better time score; ball bearings will give you less friction than any sort of "sleeve bearing"

Ah okay, thanks for the clarification.

This has been really helpful, thank you everyone. So, if I buy the bearings separately, do they have to screw into the threaded axle I buy, or can I just use them for the wheels and secure the wheels with nuts and bolts? Sorry if that is confusing, I am worried that I won't be able to find bearings that fit snug into the threaded axles.

questionguy wrote:This has been really helpful, thank you everyone. So, if I buy the bearings separately, do they have to screw into the threaded axle I buy, or can I just use them for the wheels and secure the wheels with nuts and bolts? Sorry if that is confusing, I am worried that I won't be able to find bearings that fit snug into the threaded axles.

For sumobots last year (while not the same exact concept, accuracy and precision wheel-wise was important) I just fit my wheels onto the axle and secured them with adjustable nuts. You should be okay with securing them in that fashion.

questionguy wrote:I am worried that I won't be able to find bearings that fit snug into the threaded axles.

You can. just plan ahead before you buy your axles, find bearings of the same size.

Frogger4907 wrote:

questionguy wrote:I am worried that I won't be able to find bearings that fit snug into the threaded axles.

You can. just plan ahead before you buy your axles, find bearings of the same size.

This works better than my suggestion.

OldSpice wrote:

Frogger4907 wrote:

questionguy wrote:I am worried that I won't be able to find bearings that fit snug into the threaded axles.

You can. just plan ahead before you buy your axles, find bearings of the same size.

This works better than my suggestion.

Yup - second the motion. In fact, you can get bearings that are "slip fit"-slide easily onto the axle, or into the wheel, but have essentially no slop, and "press fit"- where they will go on, but it takes some pressure to push them into place.

Getting down to the "pretty fine detail" level for a second, for those looking for that last few percent of performance, there is a set of issues to be considered and worked through when setting up/using bearings to minimize rolling friction. These were pretty easy to deal with in Mousetrap vehicles (with relatively low weight and low velocity). They will be more challenging with the higher mass and velocity we're dealing with in Gravity vehicles. There are two inter-related major aspects; bearing alignment, and side-to-side wheel/axle movement. You can have the bearings with a tight fit to the axle - and the wheels firmly fixed to the axle, and then you need to mount the bearing which are carrying the axle with attached wheels, and the whole axle rotates; you can have the bearings with a tight fit into the wheels, where you firmly mount the axle, and the wheels rotate about the fixed axle.

In the first instance- rotating axle - the challenge is getting the two holes into whatever the pieces that hold the bearings axially aligned. You have to be careful that when and how you "lock down" the bearings - hold them in-place so the axle can't move side-to-side along its axis-that you don't put any "binding" in (have the bearing where its not perfectly vertical to the axle. In the second instance,fixed axle with bearings in wheels riding on it, you'll need a way to keep the bearings from sliding along the axle that doesn't add friction - something that contacts just the inner race of the bearing, and doesn't rub against the parts of the bearing that rotate.

Little things to think about, that will make a little bit of difference....

This is all amazing stuff.

I don't know if this question has been asked already, but looking through the majority of the forum, I don't think it has.

For the frame that you would potentially be attaching a surface to, would using ribs in intervals provide as much support as an curved block of wood. My reasoning is that I don't know if I have the tools available to build/cut out a curved block, and making ribs would be definitely much easier, and if I made an error in cutting, would be relatively simple to correct that mistake.