Gravity Vehicle C

Locked
User avatar
sciolyperson1
Exalted Member
Exalted Member
Posts: 1074
Joined: April 23rd, 2018, 7:13 pm
Division: C
State: NJ
Pronouns: He/Him/His
Has thanked: 529 times
Been thanked: 601 times
Contact:

Re: Gravity Vehicle C

Post by sciolyperson1 »

chessbucket wrote: September 11th, 2019, 7:19 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.
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.
SoCal Planning Team & BirdSO Tournament Director
WW-P HSN '22, Community MS '18
Sciolyperson1's Userpage
User avatar
lindsmaurer
Member
Member
Posts: 48
Joined: May 16th, 2018, 11:57 am
Division: C
State: OH
Has thanked: 2 times
Been thanked: 3 times

Re: Gravity Vehicle C

Post by lindsmaurer »

Does anyone have any ideas on how to keep the vehicle going straight when going down the ramp?
Solon HS Captain
DMAH
Sassy #137
1-3 placements: 58
Medals + ribbons: 109

Fossils: X/2/3
Code: 2/1/10
Sounds: 1/2/11
Detector: 1/2/X
Circuits: 8/X/X
Gravity: 7/X/X
GLM: X\X\X
User avatar
windu34
Staff Emeritus
Staff Emeritus
Posts: 1383
Joined: April 19th, 2015, 6:37 pm
Division: Grad
State: FL
Has thanked: 2 times
Been thanked: 40 times

Re: Gravity Vehicle C

Post by windu34 »

killer225whale wrote: September 13th, 2019, 11:41 pm
PM2017 wrote: September 10th, 2019, 10:20 pm
windu34 wrote: September 8th, 2019, 11:09 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.
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).
Boca Raton Community High School Alumni
University of Florida Science Olympiad Co-Founder
Florida Science Olympiad Board of Directors
[email protected] || windu34's Userpage
killer225whale
Member
Member
Posts: 31
Joined: November 23rd, 2009, 9:28 pm
Has thanked: 0
Been thanked: 0

Re: Gravity Vehicle C

Post by killer225whale »

windu34 wrote: September 15th, 2019, 12:01 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.
User avatar
PM2017
Member
Member
Posts: 524
Joined: January 20th, 2017, 5:02 pm
Division: Grad
State: CA
Has thanked: 23 times
Been thanked: 13 times

Re: Gravity Vehicle C

Post by PM2017 »

killer225whale wrote: September 15th, 2019, 8:19 am 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.
West High '19
UC Berkeley '23

Go Bears!
User avatar
windu34
Staff Emeritus
Staff Emeritus
Posts: 1383
Joined: April 19th, 2015, 6:37 pm
Division: Grad
State: FL
Has thanked: 2 times
Been thanked: 40 times

Re: Gravity Vehicle C

Post by windu34 »

PM2017 wrote: September 15th, 2019, 4:27 pm
killer225whale wrote: September 15th, 2019, 8:19 am 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.
You could also use springs and store the additional energy in that.
Boca Raton Community High School Alumni
University of Florida Science Olympiad Co-Founder
Florida Science Olympiad Board of Directors
[email protected] || windu34's Userpage
User avatar
mnoga
Member
Member
Posts: 142
Joined: March 19th, 2015, 6:12 pm
Division: C
State: CA
Has thanked: 2 times
Been thanked: 8 times

Re: Gravity Vehicle C

Post by mnoga »

lindsmaurer wrote: September 14th, 2019, 7:43 am Does anyone have any ideas on how to keep the vehicle going straight when going down the ramp?
Use a rail or guide system. I will not get into specifics, but there are many possible implementations and you can get clues by observing train systems, monorail systems, ski jumping and bobsled competitions, just to name a few.
Lorant
Member
Member
Posts: 62
Joined: February 18th, 2019, 2:18 pm
Division: C
State: FL
Has thanked: 2 times
Been thanked: 1 time

Re: Gravity Vehicle C

Post by Lorant »

windu34 wrote: September 15th, 2019, 5:09 pm
PM2017 wrote: September 15th, 2019, 4:27 pm
killer225whale wrote: September 15th, 2019, 8:19 am 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.
You could also use springs and store the additional energy in that.
Is there a way to use a spring to slow down the progress of the wingnut across the threaded rod without locking it up? I'm just thinking, if you don't use two springs, or even if you do, one is bound to be marginally stronger than the other, putting the wingnut at an angle relative to the threaded rod should lock it up quite quickly shouldn't it? Is there a way to get around this?
I build. A lot.
Boca Raton High School.
Events: Boomi, Gravity Vehicle, Wright Stuff.
Incomplete Userpage
User avatar
lindsmaurer
Member
Member
Posts: 48
Joined: May 16th, 2018, 11:57 am
Division: C
State: OH
Has thanked: 2 times
Been thanked: 3 times

Re: Gravity Vehicle C

Post by lindsmaurer »

Lorant wrote: September 17th, 2019, 7:31 pm
windu34 wrote: September 15th, 2019, 5:09 pm
PM2017 wrote: September 15th, 2019, 4:27 pm
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.
You could also use springs and store the additional energy in that.
Is there a way to use a spring to slow down the progress of the wingnut across the threaded rod without locking it up? I'm just thinking, if you don't use two springs, or even if you do, one is bound to be marginally stronger than the other, putting the wingnut at an angle relative to the threaded rod should lock it up quite quickly shouldn't it? Is there a way to get around this?
First of all, wingnuts don't lock up quite that easily, as long as you have the right wingnut. Second, why not put a spring around the threaded rod so that the wingnut is centered on the spring? It may still be at a slight angle, but again, wingnuts need quite a bit of force to lock up.
Solon HS Captain
DMAH
Sassy #137
1-3 placements: 58
Medals + ribbons: 109

Fossils: X/2/3
Code: 2/1/10
Sounds: 1/2/11
Detector: 1/2/X
Circuits: 8/X/X
Gravity: 7/X/X
GLM: X\X\X
User avatar
windu34
Staff Emeritus
Staff Emeritus
Posts: 1383
Joined: April 19th, 2015, 6:37 pm
Division: Grad
State: FL
Has thanked: 2 times
Been thanked: 40 times

Re: Gravity Vehicle C

Post by windu34 »

lindsmaurer wrote: September 18th, 2019, 5:12 am
Lorant wrote: September 17th, 2019, 7:31 pm
windu34 wrote: September 15th, 2019, 5:09 pm
You could also use springs and store the additional energy in that.
Is there a way to use a spring to slow down the progress of the wingnut across the threaded rod without locking it up? I'm just thinking, if you don't use two springs, or even if you do, one is bound to be marginally stronger than the other, putting the wingnut at an angle relative to the threaded rod should lock it up quite quickly shouldn't it? Is there a way to get around this?
First of all, wingnuts don't lock up quite that easily, as long as you have the right wingnut. Second, why not put a spring around the threaded rod so that the wingnut is centered on the spring? It may still be at a slight angle, but again, wingnuts need quite a bit of force to lock up.
Agreed, the difference in force shouldnt be enough to lock it up, and this approach could be a good option. The idea with moving the center of gravity was to accomplish two things: optimize potential energy at the beginning and prepare the vehicle for braking. While it may be too complicated for most competitors, the benefits may be larger than many of us suspect, and I think it could very well be worth looking into for those with experience building high-tier devices already. Having springs in parallel with the wingnut could certainly be a good option to slow the device down, and Im curious to hear how it works out
Boca Raton Community High School Alumni
University of Florida Science Olympiad Co-Founder
Florida Science Olympiad Board of Directors
[email protected] || windu34's Userpage
Locked

Return to “Gravity Vehicle C”

Who is online

Users browsing this forum: No registered users and 2 guests