Gravity Vehicle C

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Re: Gravity Vehicle C

Postby MTV<=>Operator » September 20th, 2019, 3:22 pm

what would be the advantage of adjustable height?
In my opinion, there is none.
I don't think there is any use for that this year. Lowering the height would only cause the vehicle to lose energy.

I have a few questions of my own about materials:
1) Does anyone happen know how strong 1 cm by 1 cm extruded V-slot aluminum is? I want to make a chassis out of this, given that it is much cheaper than carbon fiber, but I have never worked with extruded aluminum before.
2) For other options I was thinking of laser cutting a plate with 6 mm thick abs plastic or 1/2" balsa wood laminated with thin carbon fiber sheets. Once again, I haven't worked with any of these materials before on a large scale, so I don't know how practical each idea is
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Re: Gravity Vehicle C

Postby T&J101 » September 21st, 2019, 9:27 am

One thing that I've never figured out in my time in vehicle events such as mousetrap vehicle and scrambler was (a) How do high skill competitors get threaded rods into ball bearings such that there is no play between the rod and the bearings, (b) it seems that an adjustable start height for the vehicle would be best but how did teams do that in the past? I may be wrong, but with heavy vehicles this year it seems that bearings are a must. Also, the only way to accurately cut the ramp that I've thought of is to laser cut. What is the recommended wheel durometer, I've heard banebot wheels are good but what durometer is best? Last year in MV I got the hubs to the axle by tightening with two wingnuts, so I was wondering how other teams did it. In a bit of a noob, so I'm sorry for a barrage of questions. : |
I'm definitely not the most qualified to answer your questions, but here is my take on things:
(a) I was thinking of getting bearings with an extended inner ring and fixing them in place on the axle with one nut on either side of the bearing. The extended inner ring would make sure the nuts don't interfere with the motion of the bearing
(b) For an adjustable launch height, you can design your launch mechanism to be bolted to the ramp surface or ramp sides. Then, make multiple holes along the surface or sides of the ramp so that the whole launch mechanism can be moved to the locations of the different holes.
As for ramp making, laser cutting would probably be by far the most accurate option, but most people don't have one available to them. To cut the sides, I believe you could use plywood, maybe 3/16 to 1/4 in thick and cut out the profile with some sort of saw. There are also options to support the ramp without the need for accurate cutting, such as vertical supports that are on either side and at multiple heights.
Yes, banebots wheels are good, and the best shore hardness will likely depend on the mass distribution of your vehicle. You want the wheels to have a soft enough hardness to provide sufficient traction, but not so soft that they cause extra friction and slow the vehicle down.
This is a good answer. Only thing I would add is the following:
a.) Many teams will make an insert to fit between the rod and bearing to get a "interference fit". I always 3D printed a thin insert, but you could certainly do it other ways.
b.) I would argue against an adjustable height. Work on your braking mechanism to adapt for different distances.
First off I thought that the lower the start height it would factor into a higher score but if that’s not the case then it seems like a rigid set height is best.
I don’t get what you mean by an interference ring for the axle and the bearing. Is it threaded and very thin so it can be glued to the bearing or is it attached with nuts. If you could explain that would be really great.(sorry I’m having trouble understanding )

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Re: Gravity Vehicle C

Postby knightmoves » September 21st, 2019, 9:44 am


I don’t get what you mean by an interference ring for the axle and the bearing. Is it threaded and very thin so it can be glued to the bearing or is it attached with nuts. If you could explain that would be really great.(sorry I’m having trouble understanding )
An "interference fit" means that a piece is very slightly bigger than the hole that it fits into. So once you've forced it together, friction keeps it from moving. In this context, it means threading a short plastic tube around the threaded rod, and then forcing the plastic tube into the bearing.

The idea is that you don't need glue, and it will stay put.

If you're tempted to glue something, make sure you don't get glue in the bearings.

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Re: Gravity Vehicle C

Postby T&J101 » September 21st, 2019, 1:32 pm


I don’t get what you mean by an interference ring for the axle and the bearing. Is it threaded and very thin so it can be glued to the bearing or is it attached with nuts. If you could explain that would be really great.(sorry I’m having trouble understanding )
An "interference fit" means that a piece is very slightly bigger than the hole that it fits into. So once you've forced it together, friction keeps it from moving. In this context, it means threading a short plastic tube around the threaded rod, and then forcing the plastic tube into the bearing.

The idea is that you don't need glue, and it will stay put.

If you're tempted to glue something, make sure you don't get glue in the bearings.
Got it that makes much more sense. But would this eliminate the need for nuts to tighten the rod against the interference fit or the bearing?

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Re: Gravity Vehicle C

Postby windu34 » September 21st, 2019, 6:16 pm


I don’t get what you mean by an interference ring for the axle and the bearing. Is it threaded and very thin so it can be glued to the bearing or is it attached with nuts. If you could explain that would be really great.(sorry I’m having trouble understanding )
An "interference fit" means that a piece is very slightly bigger than the hole that it fits into. So once you've forced it together, friction keeps it from moving. In this context, it means threading a short plastic tube around the threaded rod, and then forcing the plastic tube into the bearing.

The idea is that you don't need glue, and it will stay put.

If you're tempted to glue something, make sure you don't get glue in the bearings.
Got it that makes much more sense. But would this eliminate the need for nuts to tighten the rod against the interference fit or the bearing?
Correct nuts would not be "needed", but I would probably still recommend lock nuts to ensure there is no slippage. You dont want to tighten nuts against the bearings and risk damage to the bearings because the tolerances are pretty small
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Re: Gravity Vehicle C

Postby T&J101 » September 21st, 2019, 7:13 pm



An "interference fit" means that a piece is very slightly bigger than the hole that it fits into. So once you've forced it together, friction keeps it from moving. In this context, it means threading a short plastic tube around the threaded rod, and then forcing the plastic tube into the bearing.

The idea is that you don't need glue, and it will stay put.

If you're tempted to glue something, make sure you don't get glue in the bearings.
Got it that makes much more sense. But would this eliminate the need for nuts to tighten the rod against the interference fit or the bearing?
Correct nuts would not be "needed", but I would probably still recommend lock nuts to ensure there is no slippage. You dont want to tighten nuts against the bearings and risk damage to the bearings because the tolerances are pretty small
Ok, that makes much more sense. But the way I've been attaching bearings and metal spacers into the chassis is by forcing it into the wood and 3d printed chassis. This year aluminum chassis is basically a must because of the increased forces but how would you attach it into the chassis. All I've thought off is to add a 3 printed block with the bearing to increase the width of the aluminum chassis and increase the stability of the bearing. Any thoughts?

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Re: Gravity Vehicle C

Postby MTV<=>Operator » September 21st, 2019, 7:53 pm



Got it that makes much more sense. But would this eliminate the need for nuts to tighten the rod against the interference fit or the bearing?
Correct nuts would not be "needed", but I would probably still recommend lock nuts to ensure there is no slippage. You dont want to tighten nuts against the bearings and risk damage to the bearings because the tolerances are pretty small
Ok, that makes much more sense. But the way I've been attaching bearings and metal spacers into the chassis is by forcing it into the wood and 3d printed chassis. This year aluminum chassis is basically a must because of the increased forces but how would you attach it into the chassis. All I've thought off is to add a 3 printed block with the bearing to increase the width of the aluminum chassis and increase the stability of the bearing. Any thoughts?
As for how to attach the bearings to the chassis, I believe you could just 3D print bearing blocks and bolt them to the chassis as you said. I am planning on simply press-fitting the bearings into the blocks and then holding the bearings in place with shaft collars.

Also, in terms of aluminum, would a rectangle made from 1 cm x 1 cm extruded aluminum be strong enough? I want the chassis alone without the weights to be as light and as strong as possible. I don't know if a 6 mm thick abs plate would serve as a better chassis than aluminum or not.
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Re: Gravity Vehicle C

Postby MadCow2357 » September 22nd, 2019, 6:23 am


Correct nuts would not be "needed", but I would probably still recommend lock nuts to ensure there is no slippage. You dont want to tighten nuts against the bearings and risk damage to the bearings because the tolerances are pretty small
Ok, that makes much more sense. But the way I've been attaching bearings and metal spacers into the chassis is by forcing it into the wood and 3d printed chassis. This year aluminum chassis is basically a must because of the increased forces but how would you attach it into the chassis. All I've thought off is to add a 3 printed block with the bearing to increase the width of the aluminum chassis and increase the stability of the bearing. Any thoughts?
As for how to attach the bearings to the chassis, I believe you could just 3D print bearing blocks and bolt them to the chassis as you said. I am planning on simply press-fitting the bearings into the blocks and then holding the bearings in place with shaft collars.

Also, in terms of aluminum, would a rectangle made from 1 cm x 1 cm extruded aluminum be strong enough? I want the chassis alone without the weights to be as light and as strong as possible. I don't know if a 6 mm thick abs plate would serve as a better chassis than aluminum or not.
I would recommend another option if you don't have access to a 3d printer, or just don't want to use your time to design bearing blocks. ServoCity has an excellent selection of bearing blocks (aluminum :D ). I bought the 1/4" quad blocks last year for battery buggy, and they worked great. Personally, I never found the need to secure the axle to the inner ring of the bearings, but you could try liquid nail (recommended by a Home Depot dude).

1 cm extruded aluminum should definitely be strong enough. I used 3/4" by 1/2" last year for battery buggy, and it worked fine. Not sure how being extruded would affect the strength though. I wouldn't use ABS over aluminum since it warps a ton.
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Re: Gravity Vehicle C

Postby xiangyu » September 22nd, 2019, 7:01 am

I see everyone is talking about using aluminum for their chassis. I'm thinking about using Carbon Fiber filament to print mine. Would that be weaker than aluminum?

Also, since no one talked about this yet, would a 3 wheel vehicle design have an advantage since there will be less friction?
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Re: Gravity Vehicle C

Postby MadCow2357 » September 22nd, 2019, 4:54 pm

I see everyone is talking about using aluminum for their chassis. I'm thinking about using Carbon Fiber filament to print mine. Would that be weaker than aluminum?

Also, since no one talked about this yet, would a 3 wheel vehicle design have an advantage since there will be less friction?
I was planning on doing the exact same thing, though I'll be ordering carbon fiber rods online instead of 3d printing them (can't say I wouldn't be jealous if you actually have access to a 3d printer that can use CF :P ). Obviously the size of the rod/stick used will make a difference in the strength, but aluminum still has the edge when it comes down to durability and strength.

In my opinion, yes, 3 wheels are optimal for this year. If you have done pinewood derby before, it's the same thing as slightly lifting one wheel up so the car rolls down on 3 wheels instead of 4. However, the reason to use 3 wheels is not reduced friction, since the weight on each wheel just increases (therefore about the same amount of friction). The real reason is rotational inertia, meaning that 3 wheels are better than 4 wheels in the sense that you need to get one less wheel spinning. Please forgive me if I messed up my physics.
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