Gravity Vehicle C

[Balsa Man]

Getting back on a couple questions from Illusionist:

“Based on your description, I'm envisioning something like this: http://woodgears.ca/gear/bearing_mount2.jpg , where the wood piece is as thick as the bearing (the outside faces of the bearing are flush with the outside faces of the wood).
Now with a design like that, how do you prevent the bearing from slipping out of the holder? The image I've linked to above shows a a screw used to tighten the wood and grasp the bearing. Any other options? A couple self-threading set screws coming in from the top and bottom of the wooden holder might be able to be used.”

What we’re using is sort of like that. We’re using flanged bearings- there is a little lip around one edge of the outer bearing race- its on the order of 1/64th” thick, w/ a radius about 1/64th bigger than the race. So when the bearing goes into a ¼” hole- a ¼” square hole- the flange catches the edges, and stops the bearing from going on through the hole. Then on two sides, we run little retaining strips- out of 1/16th” thick lexan, ¼” x ½”. Along one edge, there’s a little cut-out. The cross section of that cut-out is a little bigger than 1/64th x 1/64th”, like a few thousandths bigger. So, when you glue two of these strips onto the bearing carrier plate, with the cut-out edge against the bearing, they overlap the flange, so the bearing can’t come back out of the hole. Looking down the axle, the flange now locks the bearing from moving in/away from you (because its catching the edges of the ¼ x ¼ hole), and it locks the bearing from moving out/toward you, because its catching the retaining strips.

Now, here’s the key difference in this setup, and the one shown in your link. The advantages of what I’m about to describe are small (unless your axle is seriously not straight and/or the planes of your bearings are way off being parallel and vertical to the axle)- this alone won’t make ‘the winning difference.’ But if you put enough little, advantageous differences together, they can add up to a measurable, positive difference. For a live axle, in the perfect case, your axle is perfectly straight, and the bearings are perfectly parallel, and perpendicular to the axle; the friction is that designed into/inherent in the bearings. However, if the bearing planes are not parallel, and/or if the axle is not perfectly straight, and if the bearing alignments are.....locked down- anchored in a way that the bearing can’t move – like in the setup you’re showing- then you get some amount of binding, and flexing of the axle; friction is higher, the vehicle slows down faster than it would with ‘ideal” alignment. You can see this effect if you set up a little test jig- a piece of board as wide as the distance between your bearings. On that, glue on a couple of strips that are the width of your bearings. Mount them on the top of the board, at and along the edges, so they are parallel. So, if you take your axle, with the wheels attached, and put it across these strips, the bearings will ride on top of the strips. On top of those strips, on one side of the axle, on each side, glue a little block butting up against the bearing. Then across the axle from each bearing, glue down another holder block. When you glue these second blocks on, slip a piece of paper in between the bearing and the block. Position the block so that with the paper shim in place, its nice and snug against the bearing. Pull the paper out, and you’ll have 2-3 thousandths of an inch free-play. Now spin the axle up. Looking down on the bearings, unless you’re incredibly lucky and you’re axle is perfectly straight, you will see the bearings wobble.

So, you want the bearing locations “fixed’- where the bearing can’t move fore and aft, so you don’t get....”steering wander”, but you also want the (plane of) the bearing to be able to wobble around the axis of the axle. Here’s how we got both.
Bearing o.d. is ¼”, bearing width is 1/18th”, bearing holder plates are 1/8th thickness, flanges on one side of the bearings. Bearing holder holes are ¼” square (mark, cut/grind to close, then carefully work with a little file-file; check, fit, file some more, check fit, etc., etc.-till you get a nice snug fit. The inside edges of the bearing hole will be flat, and will fit flat against the flat outside of the bearing’s outer race; the bearing will essentially not be able to wobble. Now, from the side of the bearing holder plate away from the flange, using your little, file you want to taper the hole; file away the edge that’s away from the flange. Angle doesn’t matter much, say 20 degrees. As you file more, the edge of your cut will move toward the flange side. File till on the flange side you still have a little un-filed material, say 1/32nd to 1/64th. Be careful not to file/cut into the edge of the hole on the flange side. When you’ve done all 3 sides, on your flange side, your hole, the hole will still be the exact ¼ x ¼ you started with; on the other side, it will be more like 5/16ths x 5/16ths. Because you left the flange side of the hole alone, the bearing will still fit snugly. But, now, because the bearing is only riding on the thin edge, it can wobble.

Two things to finish up. The flange retainer strips I mentioned earlier have to have enough clearance in the cut-out that overlaps the flanges (some more careful file work), so that when the bearing wobbles there is room- thee flange is not pinned against the bearing holder plate. The thickness of a piece of paper- 2-3 thousandths is plenty. Put the bearing on a nice hard surface, laying on one face; put a little piece of paper on top (piece of a sticky-note works nicely). Push your bearing retainer strip, with the lip overlapping the flange, down- with file, adjust the depth to your lip so that when the lip is in contact with the flange, the face of the block is solidly in contact with the plate the bearing is sitting on. Last bit is to do your top retainer strip. It’s also out of 1/8th thick lexan, like ¼” x ¾”. In the middle one edge of it, about ¼” wide, taper the edge like you’ve done to the other 3 sides of the bearing hole. That way, when you glue it across the top of your bearing holder hole, you have a 4-sided, ¼ x ¼ hole; bearing can’t move fore and aft, or up and down, but it can wobble......

And,
“On a different topic, what types of metals are you using for the axles? I've been using Zinc threaded rods that I've found at HomeDepot. They also have stainless steel, but it's about 5 times more expensive.”
On the front – a live axle- with both wheels attached to the axle- we use 1/8th titanium; weight and stiffness.
On the rear – a dead axle- bearings in the wheels – we use 1/8th” carbon fiber.

Hope this helps.

Does anyone have any ideas on an elastic method to help propel our vehicles?

Under the rules, that's not allowed- no stored energy that contributes to the energy of the vehicle- only what you get by rolling down the ramp...See rule 3.c.

[Cheese_Muffin_Man]

Getting back on a couple questions from Illusionist:

“Based on your description, I'm envisioning something like this: http://woodgears.ca/gear/bearing_mount2.jpg , where the wood piece is as thick as the bearing (the outside faces of the bearing are flush with the outside faces of the wood).
Now with a design like that, how do you prevent the bearing from slipping out of the holder? The image I've linked to above shows a a screw used to tighten the wood and grasp the bearing. Any other options? A couple self-threading set screws coming in from the top and bottom of the wooden holder might be able to be used.”

What we’re using is sort of like that. We’re using flanged bearings- there is a little lip around one edge of the outer bearing race- its on the order of 1/64th” thick, w/ a radius about 1/64th bigger than the race. So when the bearing goes into a ¼” hole- a ¼” square hole- the flange catches the edges, and stops the bearing from going on through the hole. Then on two sides, we run little retaining strips- out of 1/16th” thick lexan, ¼” x ½”. Along one edge, there’s a little cut-out. The cross section of that cut-out is a little bigger than 1/64th x 1/64th”, like a few thousandths bigger. So, when you glue two of these strips onto the bearing carrier plate, with the cut-out edge against the bearing, they overlap the flange, so the bearing can’t come back out of the hole. Looking down the axle, the flange now locks the bearing from moving in/away from you (because its catching the edges of the ¼ x ¼ hole), and it locks the bearing from moving out/toward you, because its catching the retaining strips.

Now, here’s the key difference in this setup, and the one shown in your link. The advantages of what I’m about to describe are small (unless your axle is seriously not straight and/or the planes of your bearings are way off being parallel and vertical to the axle)- this alone won’t make ‘the winning difference.’ But if you put enough little, advantageous differences together, they can add up to a measurable, positive difference. For a live axle, in the perfect case, your axle is perfectly straight, and the bearings are perfectly parallel, and perpendicular to the axle; the friction is that designed into/inherent in the bearings. However, if the bearing planes are not parallel, and/or if the axle is not perfectly straight, and if the bearing alignments are.....locked down- anchored in a way that the bearing can’t move – like in the setup you’re showing- then you get some amount of binding, and flexing of the axle; friction is higher, the vehicle slows down faster than it would with ‘ideal” alignment. You can see this effect if you set up a little test jig- a piece of board as wide as the distance between your bearings. On that, glue on a couple of strips that are the width of your bearings. Mount them on the top of the board, at and along the edges, so they are parallel. So, if you take your axle, with the wheels attached, and put it across these strips, the bearings will ride on top of the strips. On top of those strips, on one side of the axle, on each side, glue a little block butting up against the bearing. Then across the axle from each bearing, glue down another holder block. When you glue these second blocks on, slip a piece of paper in between the bearing and the block. Position the block so that with the paper shim in place, its nice and snug against the bearing. Pull the paper out, and you’ll have 2-3 thousandths of an inch free-play. Now spin the axle up. Looking down on the bearings, unless you’re incredibly lucky and you’re axle is perfectly straight, you will see the bearings wobble.

So, you want the bearing locations “fixed’- where the bearing can’t move fore and aft, so you don’t get....”steering wander”, but you also want the (plane of) the bearing to be able to wobble around the axis of the axle. Here’s how we got both.
Bearing o.d. is ¼”, bearing width is 1/18th”, bearing holder plates are 1/8th thickness, flanges on one side of the bearings. Bearing holder holes are ¼” square (mark, cut/grind to close, then carefully work with a little file-file; check, fit, file some more, check fit, etc., etc.-till you get a nice snug fit. The inside edges of the bearing hole will be flat, and will fit flat against the flat outside of the bearing’s outer race; the bearing will essentially not be able to wobble. Now, from the side of the bearing holder plate away from the flange, using your little, file you want to taper the hole; file away the edge that’s away from the flange. Angle doesn’t matter much, say 20 degrees. As you file more, the edge of your cut will move toward the flange side. File till on the flange side you still have a little un-filed material, say 1/32nd to 1/64th. Be careful not to file/cut into the edge of the hole on the flange side. When you’ve done all 3 sides, on your flange side, your hole, the hole will still be the exact ¼ x ¼ you started with; on the other side, it will be more like 5/16ths x 5/16ths. Because you left the flange side of the hole alone, the bearing will still fit snugly. But, now, because the bearing is only riding on the thin edge, it can wobble.

Two things to finish up. The flange retainer strips I mentioned earlier have to have enough clearance in the cut-out that overlaps the flanges (some more careful file work), so that when the bearing wobbles there is room- thee flange is not pinned against the bearing holder plate. The thickness of a piece of paper- 2-3 thousandths is plenty. Put the bearing on a nice hard surface, laying on one face; put a little piece of paper on top (piece of a sticky-note works nicely). Push your bearing retainer strip, with the lip overlapping the flange, down- with file, adjust the depth to your lip so that when the lip is in contact with the flange, the face of the block is solidly in contact with the plate the bearing is sitting on. Last bit is to do your top retainer strip. It’s also out of 1/8th thick lexan, like ¼” x ¾”. In the middle one edge of it, about ¼” wide, taper the edge like you’ve done to the other 3 sides of the bearing hole. That way, when you glue it across the top of your bearing holder hole, you have a 4-sided, ¼ x ¼ hole; bearing can’t move fore and aft, or up and down, but it can wobble......

And,
“On a different topic, what types of metals are you using for the axles? I've been using Zinc threaded rods that I've found at HomeDepot. They also have stainless steel, but it's about 5 times more expensive.”
On the front – a live axle- with both wheels attached to the axle- we use 1/8th titanium; weight and stiffness.
On the rear – a dead axle- bearings in the wheels – we use 1/8th” carbon fiber.

Hope this helps.

Does anyone have any ideas on an elastic method to help propel our vehicles?

Under the rules, that's not allowed- no stored energy that contributes to the energy of the vehicle- only what you get by rolling down the ramp...See rule 3.c.

I mean, how do you guys plan to transfer the gravitational potential energy into elastic devices?

[iwonder]

I don't see why anyone would transfer the potential energy into an elastic storage device, any particular reason? Remember that any extra step the energy has to take before it moves the vehicle is going to loose energy to inefficiencies.

[Cheese_Muffin_Man]

I don't see why anyone would transfer the potential energy into an elastic storage device, any particular reason? Remember that any extra step the energy has to take before it moves the vehicle is going to loose energy to inefficiencies.

But then how do you plan your vehicle to travel the 5-10 m?

[iwonder]

Let's go back to basics here

Assume that the vehicle falls 1 meter from the top of the ramp. Assume that it weighs 1 kg, and looses one joule per meter(this is probably unreasonably high) of energy to friction in the bearings.

When the vehicle sits at the top of the ramp, it has gravitational potential energy, calculated by GPE=(mass)(accel of g)(height), so we get GPE=(1)(9.8)(1), the vehicle starts off with 9.8 Joules of energy. When the vehicle goes down the ramp, regardless of the path it takes, it's GPE is transferred into kinetic energy. KE is given by the equation KE=(mv^2)/2, so KE=((1)(v^2)/2=9.8(the energy in the system, because the conservation of energy states that this will remain constant). So this means that the vehicle is rolling down the track with that much energy, and we've shown that it now has a velocity(4.427m/s to be exact). The only way the vehicle stops is through friction, if we said that it looses 1 joule of energy per meter, then after 9.8 meters the vehicle would come to a stop.

Now, since we know that the energy in the system is only lost through friction(or something similar), and we can't have any elastic device that is storing energy at the start of the run, transferring energy into an elastic device and out of the same device will, in a perfect system, result in the exact same amount of energy going to the wheels as it would have the traditional method, or, in the real world, would result in less energy in the system(because of losses) getting to move the vehicle forward than the traditional method.

Balsaman or one of the other coaches could probably explain better, but basically you just roll the vehicle off the ramp, and as long as you don't have too much friction, it'll go as far as you need, by adding some elastic device you only further complicate it. Remember, high level vehicles are able to travel upwards of 35 meters just by rolling down the ramp before friction slows them to a stop.

Also, if I completely misunderstood your question, sorry

[Balsa Man]

Yup, iwonder has it right. Your original question was how to use elastic (energy) to "propel" the vehicle.
First, by the rules, you can't. Second, gravity provides plenty energy to go way beyond 10 meters- there's no need, even if you could.
Do you, by chance mean how to use elastic to absorb energy - as in a braking system, so the brakes go on....progressively, instead of just slamming on, causing lockup and skidding??

[Cheese_Muffin_Man]

Let's go back to basics here

Assume that the vehicle falls 1 meter from the top of the ramp. Assume that it weighs 1 kg, and looses one joule per meter(this is probably unreasonably high) of energy to friction in the bearings.

When the vehicle sits at the top of the ramp, it has gravitational potential energy, calculated by GPE=(mass)(accel of g)(height), so we get GPE=(1)(9.8)(1), the vehicle starts off with 9.8 Joules of energy. When the vehicle goes down the ramp, regardless of the path it takes, it's GPE is transferred into kinetic energy. KE is given by the equation KE=(mv^2)/2, so KE=((1)(v^2)/2=9.8(the energy in the system, because the conservation of energy states that this will remain constant). So this means that the vehicle is rolling down the track with that much energy, and we've shown that it now has a velocity(4.427m/s to be exact). The only way the vehicle stops is through friction, if we said that it looses 1 joule of energy per meter, then after 9.8 meters the vehicle would come to a stop.

Now, since we know that the energy in the system is only lost through friction(or something similar), and we can't have any elastic device that is storing energy at the start of the run, transferring energy into an elastic device and out of the same device will, in a perfect system, result in the exact same amount of energy going to the wheels as it would have the traditional method, or, in the real world, would result in less energy in the system(because of losses) getting to move the vehicle forward than the traditional method.

Balsaman or one of the other coaches could probably explain better, but basically you just roll the vehicle off the ramp, and as long as you don't have too much friction, it'll go as far as you need, by adding some elastic device you only further complicate it. Remember, high level vehicles are able to travel upwards of 35 meters just by rolling down the ramp before friction slows them to a stop.
Thanks a ton. That clears a lot of things up.

Also, if I completely misunderstood your question, sorry

[Cheese_Muffin_Man]

Let's go back to basics here

Assume that the vehicle falls 1 meter from the top of the ramp. Assume that it weighs 1 kg, and looses one joule per meter(this is probably unreasonably high) of energy to friction in the bearings.

When the vehicle sits at the top of the ramp, it has gravitational potential energy, calculated by GPE=(mass)(accel of g)(height), so we get GPE=(1)(9.8)(1), the vehicle starts off with 9.8 Joules of energy. When the vehicle goes down the ramp, regardless of the path it takes, it's GPE is transferred into kinetic energy. KE is given by the equation KE=(mv^2)/2, so KE=((1)(v^2)/2=9.8(the energy in the system, because the conservation of energy states that this will remain constant). So this means that the vehicle is rolling down the track with that much energy, and we've shown that it now has a velocity(4.427m/s to be exact). The only way the vehicle stops is through friction, if we said that it looses 1 joule of energy per meter, then after 9.8 meters the vehicle would come to a stop.

Now, since we know that the energy in the system is only lost through friction(or something similar), and we can't have any elastic device that is storing energy at the start of the run, transferring energy into an elastic device and out of the same device will, in a perfect system, result in the exact same amount of energy going to the wheels as it would have the traditional method, or, in the real world, would result in less energy in the system(because of losses) getting to move the vehicle forward than the traditional method.

Balsaman or one of the other coaches could probably explain better, but basically you just roll the vehicle off the ramp, and as long as you don't have too much friction, it'll go as far as you need, by adding some elastic device you only further complicate it. Remember, high level vehicles are able to travel upwards of 35 meters just by rolling down the ramp before friction slows them to a stop.
Thanks a ton. That clears a lot of things up.


Also, if I completely misunderstood your question, sorry

Thanks a ton. That clears a lot of things up.

[Cheese_Muffin_Man]

Yup, iwonder has it right. Your original question was how to use elastic (energy) to "propel" the vehicle.
First, by the rules, you can't. Second, gravity provides plenty energy to go way beyond 10 meters- there's no need, even if you could.
Do you, by chance mean how to use elastic to absorb energy - as in a braking system, so the brakes go on....progressively, instead of just slamming on, causing lockup and skidding??

No, I did not. iwonder answered my question awesomely!

[illusionist]

This is about a specific scenario and how it relates to the rules. I realize all answers are simply opinions as they aren't posted on soinc.org, etc., etc.

The rules state that "competitors must release the vehicle by using any part of an unsharpened #2 pencil, with an unused eraser... to actuate teh release mechanism on the ramp... Competitors must not use the pencil to touch any part of the vehicle to start the run"

My plan is to use the ES-provided pencil to pull string that will in turn pull out another pencil on the ramp.

The rules state that "an" ES-provided pencil may be used. Is the intention behind this that you can only use one pencil, and that will be provided by the ES, or that there is no restriction about the number of pencils, but one of them must be the one that is provided by the ES?

Would using something like a wooden dowel instead for the second part that I described in my plan be legal under the rules? It serves the same purpose as the pencil though.

I know official clarifications don't open up on soinc.org until the 15th, so I came here to ask for opinions. I know that Mr. Anderson and Mr. Chalker stated that they didn't want to give clarifications on specific scenarios, so I won't take any responses to this as anything close to official.

Btw, thank you very much Balsa Man for the detailed description. It's definitely got me thinking of some new ideas.