Gravity Vehicle C

AngelMB
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Re: Gravity Vehicle C

Postby AngelMB » September 11th, 2019, 7:47 pm

I don't know if this is appropriate to put here but I wanted to get other's opinions on this:

Why would they make the distance so long? 12 meters?!?!

This may be unique to my situation but the way our team does building events is the kids do it 99% at home. Most building and testing time is done on weekends and over breaks, which is conveniently when school tends to be closed, so we can't use a hallway or anything like that to test. We don't do scioly as a club after school or during school. Where do you guys test? I've thought about a community center but having to keep transporting builds can 1) increase the chances of something breaking in transport, and 2) constantly changing testing surfaces and locations can introduce confounding variables when ur trying to get sub 5cm accuracy. For MTV, we had a continuous stretch of 8m in the common area of my house, so we always had a constant variable that didn't affect runs differently. with the 12 meter distance this year, it's a different story. I apologize if I sound like I'm whining, venting, and/or ranting but having a constant test surface has always proved to be a must in my experience.
I have had success using the hallway of a local university, maybe if you have a local university you could do the same? Like you suggested, a community center with sufficient space could be used. I would also suggest asking the other members of your team to see if they have space in their house or have a club house in their community that could be used for testing. I've also done that in the past and had a good time connecting with other teammates as a result. In general, I would just say look for any good floor and take advantage of any time you have to test. Although it may be annoying to have to set up multiple tracks, having to test on multiple floors should allow you to be able to tell how your vehicle's runs will differ on different types of floors for different competitions.
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Re: Gravity Vehicle C

Postby Things2do » September 11th, 2019, 8:08 pm

I utilize a hallway in a climate-controlled storage unit building. The cracks are about 13m apart, but it was only 1/2 the necessary track width last year. I just started on one side and let my car curve back to that side, and ignored the half of the Rules track that my car never touched...
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Re: Gravity Vehicle C

Postby windu34 » September 11th, 2019, 9:43 pm

I don't know if this is appropriate to put here but I wanted to get other's opinions on this:

Why would they make the distance so long? 12 meters?!?!

This may be unique to my situation but the way our team does building events is the kids do it 99% at home. Most building and testing time is done on weekends and over breaks, which is conveniently when school tends to be closed, so we can't use a hallway or anything like that to test. We don't do scioly as a club after school or during school. Where do you guys test? I've thought about a community center but having to keep transporting builds can 1) increase the chances of something breaking in transport, and 2) constantly changing testing surfaces and locations can introduce confounding variables when ur trying to get sub 5cm accuracy. For MTV, we had a continuous stretch of 8m in the common area of my house, so we always had a constant variable that didn't affect runs differently. with the 12 meter distance this year, it's a different story. I apologize if I sound like I'm whining, venting, and/or ranting but having a constant test surface has always proved to be a must in my experience.
As others have mentioned, there are plenty of places to test. I have heard of things as crazy as testing scrambler at Walmart at 1am. All you need to find is a smooth floor - friction coefficients are not wildly different and gravity vehicle is one of the slower vehicle events (compared to scrambler, EV). Community centers, university hallways, random stores (if you can get permission, it can be an option), it goes on and on.
As for transporting, yeah its not ideal. I suggest putting the ramp on wheels for convenience.
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Re: Gravity Vehicle C

Postby lindsmaurer » September 12th, 2019, 7:50 am

Hi, I'm new to this event and had a few questions:

What are the vehicle and ramp supposed to be made out of?

Any resources on how to build a release mechanism?

How is the machine held vertically in the starting position? Does the release mechanism hold it up?

Any tips on how to get the vehicle to move as slowly as possible while still reaching as close to the target as possible?

Thanks!
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4. Why would you want it to move as slowly as possible? Speed is important!
I'm guessing you (Annabelle) notice the lower score for faster time. This event is scored such that the lowest score wins, so you want the fastest time possible.
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Re: Gravity Vehicle C

Postby killer225whale » September 13th, 2019, 11:41 pm

This brings up an interesting point of discussion: would it be possible to move the center of mass during the run of your vehicle? In the ready to run position, Id estimate wanting about 90% of the mass in the rear, but after the vehicle has descended down the ramp, it is more advantageous to have about 60-70% of the mass in the rear to prevent significant understeer and to aid in uniform braking. Perhaps it is possible to actually have the center of mass MOVE during the run. This could potentially be done near the end of the run (after 6-7 meters have been traveled) as a means of reducing vehicle speed. I envision a simple string wrapping around an axle after a certain distance has passed that moves the center of mass forward.
Food for thought. Id be interested to hear others' perspectives on this.
Legality aside, this seems a bit complicated from a technical perspective, because you'd need to have some sort of latch that starts off closed (otherwise the mass would simply slide down when in the ready-to-run). I think it definitely can be done, though. (also I don't know about the legality of this, but could it perhaps hit part of the ramp on the way down that opens the latch? Even if legal, I'm not sure it would be viable because it would take out a large chunk of momentum if not executed very well down, and have to be able to accomodate the dowel, which would likely mean assymetry, in which case any imperfection would mean the car could slightly swerve, causing some major accuracy issues)

The other issue is how much friction the moving mass would have. I wonder if you could build the whole vehicle around a linear slide as a chassis.

IDK how rational this is, but I think that much mass shifting on a vehicle should be pretty scary. OTOH, it would be pretty epic lol.

These thoughts are not fully fleshed out but I'm sort of sleepy, so we'll see what sort of glaring mistakes I've made tomorrow...
If you wanted to use some movable mass to slow down your vehicle, you can't just move the CoM forward - you'd have to move the CoM to a higher height (i.e. convert some of your kinetic energy back into gravitational potential energy.) You might be able to do this by having a heavy mass on some kind of pivot, and a string would pull it up beyond a certain point.

Seems mechanically complex though, as the mass would have significant momentum, and could cause your vehicle to jerk. Additionally, you'd need to be able to lift the mass without causing the driving axle to lock up. If that axle locks up, then there would be no lifting of the mass, and all you did was (full) brake earlier than intended.

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Re: Gravity Vehicle C

Postby sciolyperson1 » September 14th, 2019, 7:36 am

I don't know if this is appropriate to put here but I wanted to get other's opinions on this:

Why would they make the distance so long? 12 meters?!?!

This may be unique to my situation but the way our team does building events is the kids do it 99% at home. Most building and testing time is done on weekends and over breaks, which is conveniently when school tends to be closed, so we can't use a hallway or anything like that to test. We don't do scioly as a club after school or during school. Where do you guys test? I've thought about a community center but having to keep transporting builds can 1) increase the chances of something breaking in transport, and 2) constantly changing testing surfaces and locations can introduce confounding variables when ur trying to get sub 5cm accuracy. For MTV, we had a continuous stretch of 8m in the common area of my house, so we always had a constant variable that didn't affect runs differently. with the 12 meter distance this year, it's a different story. I apologize if I sound like I'm whining, venting, and/or ranting but having a constant test surface has always proved to be a must in my experience.
We tested in a variety of locations last year and the year before that: the middle school's small/large gym, upper hallway, and hs's aux/main gym and a hallway. Make sure to take a look at flooring, the wood planks on the gym floor tend to not be straight, but the paint (like on the edge of the basketball court for example) does seem to be. In addition, linoleum tiles also aren't always straight. We tried avoiding areas like our MS's gyms because it was usually very dirty and full of holes, so make sure you don't run your vehicle over flooring like that.
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Re: Gravity Vehicle C

Postby lindsmaurer » September 14th, 2019, 7:43 am

Does anyone have any ideas on how to keep the vehicle going straight when going down the ramp?
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Detector Building
Fossils
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Re: Gravity Vehicle C

Postby windu34 » September 15th, 2019, 12:01 am

This brings up an interesting point of discussion: would it be possible to move the center of mass during the run of your vehicle? In the ready to run position, Id estimate wanting about 90% of the mass in the rear, but after the vehicle has descended down the ramp, it is more advantageous to have about 60-70% of the mass in the rear to prevent significant understeer and to aid in uniform braking. Perhaps it is possible to actually have the center of mass MOVE during the run. This could potentially be done near the end of the run (after 6-7 meters have been traveled) as a means of reducing vehicle speed. I envision a simple string wrapping around an axle after a certain distance has passed that moves the center of mass forward.
Food for thought. Id be interested to hear others' perspectives on this.
Legality aside, this seems a bit complicated from a technical perspective, because you'd need to have some sort of latch that starts off closed (otherwise the mass would simply slide down when in the ready-to-run). I think it definitely can be done, though. (also I don't know about the legality of this, but could it perhaps hit part of the ramp on the way down that opens the latch? Even if legal, I'm not sure it would be viable because it would take out a large chunk of momentum if not executed very well down, and have to be able to accomodate the dowel, which would likely mean assymetry, in which case any imperfection would mean the car could slightly swerve, causing some major accuracy issues)

The other issue is how much friction the moving mass would have. I wonder if you could build the whole vehicle around a linear slide as a chassis.

IDK how rational this is, but I think that much mass shifting on a vehicle should be pretty scary. OTOH, it would be pretty epic lol.

These thoughts are not fully fleshed out but I'm sort of sleepy, so we'll see what sort of glaring mistakes I've made tomorrow...
If you wanted to use some movable mass to slow down your vehicle, you can't just move the CoM forward - you'd have to move the CoM to a higher height (i.e. convert some of your kinetic energy back into gravitational potential energy.) You might be able to do this by having a heavy mass on some kind of pivot, and a string would pull it up beyond a certain point.

Seems mechanically complex though, as the mass would have significant momentum, and could cause your vehicle to jerk. Additionally, you'd need to be able to lift the mass without causing the driving axle to lock up. If that axle locks up, then there would be no lifting of the mass, and all you did was (full) brake earlier than intended.
Correct me if I am wrong on this, but my line of thinking is the following:
An independent, movable mass on the vehicle is traveling at the same velocity as all of the other components on the vehicle. If a string were to be attached to the axle and this mass and the string were to wrap around the axle and pull the mass, the string would have to exert a tensional force on the mass because the mass would be accelerated from zero in the vehicles reference frame. An equal and opposite force must be exerted at a distance from the center of rotation of the axle, resulting in a moment (torque) being applied opposite of the angular velocity vector of the axle, thus reducing its angular velocity. Since the mass is being moved a given distance within the car's reference frame, work is being done on the mass by the angular motion of the axle.

Interested to hear your thoughts. I think the difference here is you were looking at the vehicle as a single system from an outside reference point (say from an observer).
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Re: Gravity Vehicle C

Postby killer225whale » September 15th, 2019, 8:19 am

Correct me if I am wrong on this, but my line of thinking is the following:
An independent, movable mass on the vehicle is traveling at the same velocity as all of the other components on the vehicle. If a string were to be attached to the axle and this mass and the string were to wrap around the axle and pull the mass, the string would have to exert a tensional force on the mass because the mass would be accelerated from zero in the vehicles reference frame. An equal and opposite force must be exerted at a distance from the center of rotation of the axle, resulting in a moment (torque) being applied opposite of the angular velocity vector of the axle, thus reducing its angular velocity. Since the mass is being moved a given distance within the car's reference frame, work is being done on the mass by the angular motion of the axle.

Interested to hear your thoughts. I think the difference here is you were looking at the vehicle as a single system from an outside reference point (say from an observer).
You are correct that as the vehicle accelerates the mass from the vehicle's frame of reference, it will exert a braking force on the Vehicle. You're forgetting that the same has to happen to decelerate the mass from the vehicle's reference. Unless your mass can continue on a different velocity indefinitely (i.e. detach from the vehicle and continue flying off), then that reduction in speed of your vehicle will only be temporary.

The amount of kinetic energy in your Vehicle remains constant (ignoring any losses). You may have accelerated the mass briefly, but at the end of the run, the mass must be at the same speed as the vehicle. The mass will likely hit some kind of hard-stop, and just transfer that extra energy back to the vehicle.

So yes, if you look at the Vehicle as a closed system, at the end of the run, kinetic energy has to be 0. If you haven't stored any of that kinetic energy in something (like elastic or gravitational potential), then it all must have been dissipated as heat by your brakes.

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Re: Gravity Vehicle C

Postby PM2017 » September 15th, 2019, 4:27 pm

So yes, if you look at the Vehicle as a closed system, at the end of the run, kinetic energy has to be 0. If you haven't stored any of that kinetic energy in something (like elastic or gravitational potential), then it all must have been dissipated as heat by your brakes.
Actually, magnets might (emphasis on the might) be a feasible idea, that solves latch issue we mentioned earlier. If you take kinetic energy from the vehicle as a whole, store it as potential energy in magnets, you could decelerate the vehicle, while also moving the mass to the front, making the braking more accurate.
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