Gravity Vehicle C

knightmoves
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Re: Gravity Vehicle C

Postby knightmoves » October 3rd, 2019, 2:38 pm

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
...and how reliably are you able to set the start position and angle each time? If you can design your ramp to be less sensitive to exactly how you place the car on it, will you be better off?

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Re: Gravity Vehicle C

Postby PM2017 » October 3rd, 2019, 2:55 pm

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
...and how reliably are you able to set the start position and angle each time? If you can design your ramp to be less sensitive to exactly how you place the car on it, will you be better off?
I was thinking that to minimize error, a competitor might have a release mechanism involving two hooks (/whatever is used to release the car) constrained such that they only be pushed up or down vertically and such that if one hook is moved by a given amount, the other will have to move the same amount. That way, if the competitor is able to quickly disengage the hooks from the vehicle by pushing or pulling from underneath, using the pencil, the car would move the same way each time.
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Re: Gravity Vehicle C

Postby lindsmaurer » October 3rd, 2019, 4:16 pm



But how do you make sure that the guidance system is 100% straight? (or if not 100%, then better enough to warrant the extra effort?)
It doesn't have to be 100% straight As long as it is consistently released the same way each time. Once you have consistency, you can compensate for any imperfections when aiming I have no idea if a guidance system would be worth building, but I can definitely understand the thought process behind it and why it may be important in achieving consistent accuracy
Sorry, this is a pretty late reply, but then why do you even need a guidance system in the first place. If you would just adjust the direction of the ramp (which you would need to do anyways), it wouldn't make too much sense to make one.

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
In my opinion, it's harder to get it to start the same way since even a slight angle could throw it off course, but a guidance system makes it end the same every time, and is more consistent
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Re: Gravity Vehicle C

Postby sciolyperson1 » October 4th, 2019, 4:33 pm



But how do you make sure that the guidance system is 100% straight? (or if not 100%, then better enough to warrant the extra effort?)
It doesn't have to be 100% straight As long as it is consistently released the same way each time. Once you have consistency, you can compensate for any imperfections when aiming I have no idea if a guidance system would be worth building, but I can definitely understand the thought process behind it and why it may be important in achieving consistent accuracy
Sorry, this is a pretty late reply, but then why do you even need a guidance system in the first place. If you would just adjust the direction of the ramp (which you would need to do anyways), it wouldn't make too much sense to make one.

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
I don't think multiple hooks are necessary, as long you set it up consistently each time, even if it consistently goes to the right or left or whatever, it should be fine.

Kinda like my buggy for '18, it always curved a tiny, tiny bit to one side, so every time we ran the car, we'd tilt it consistently to the left a little bit so that it'd stay centered.
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Re: Gravity Vehicle C

Postby PM2017 » October 5th, 2019, 10:08 pm


It doesn't have to be 100% straight As long as it is consistently released the same way each time. Once you have consistency, you can compensate for any imperfections when aiming I have no idea if a guidance system would be worth building, but I can definitely understand the thought process behind it and why it may be important in achieving consistent accuracy
Sorry, this is a pretty late reply, but then why do you even need a guidance system in the first place. If you would just adjust the direction of the ramp (which you would need to do anyways), it wouldn't make too much sense to make one.

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
In my opinion, it's harder to get it to start the same way since even a slight angle could throw it off course, but a guidance system makes it end the same every time, and is more consistent
With gravity working to pull the car straight, this really shouldn't be an issue. From our experience with this event being a trial at socal last year, the alignment of the ramp really makes all the difference. The alignment of the car relative to the ramp was almost nonissue. (My memory could be spotty -- I was more worried about studying for astronomy and finalizing my mission possible those last two weeks than the part of the team working on trial events!)
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Re: Gravity Vehicle C

Postby Tendan » October 6th, 2019, 1:24 pm


Sorry, this is a pretty late reply, but then why do you even need a guidance system in the first place. If you would just adjust the direction of the ramp (which you would need to do anyways), it wouldn't make too much sense to make one.

This is, of course, assuming the vehicle starts moving the same way each time. (I guess the mechanism for getting this to happen -- like multiple hooks that are released at the same time -- would be a guidance system of sorts, but I had thought we were talking about something like rails.)
In my opinion, it's harder to get it to start the same way since even a slight angle could throw it off course, but a guidance system makes it end the same every time, and is more consistent
With gravity working to pull the car straight, this really shouldn't be an issue. From our experience with this event being a trial at socal last year, the alignment of the ramp really makes all the difference. The alignment of the car relative to the ramp was almost nonissue. (My memory could be spotty -- I was more worried about studying for astronomy and finalizing my mission possible those last two weeks than the part of the team working on trial events!)
With my car, it seems that the alignment that really matters is the car with the target. The ramp can be crooked, but so long as the car is lined up with the target, everything should work out. That being said, the answer could be relative to the car and ramp being used.
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Re: Gravity Vehicle C

Postby megrimlockawesom » October 7th, 2019, 9:37 am

On the wiki site, it keeps mentioning that the propulsion system puts a great deal of stress on the vehicle. Why is that the case?
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Re: Gravity Vehicle C

Postby Tendan » October 8th, 2019, 1:39 pm

On the wiki site, it keeps mentioning that the propulsion system puts a great deal of stress on the vehicle. Why is that the case?
It may be referring to an inclined plane style ramp, in which the stress would occur when the car hit the floor. Correct me if I'm wrong, but I think a curved ramp should make the strain on the chassis so negligible that there would be no need to reinforce it unless it's something like balsa.
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Re: Gravity Vehicle C

Postby kendreaditya » October 9th, 2019, 7:54 pm

I was wondering what forces could make the car, while going down the ramp, move away from the surface of the ramp in the x-direction (if x was parallel to the ground)? I was thinking it could be the center of gravity of the car in the x-direction. In other words, the CG is too high above the car. Would this be a reason why my car does this?

Another question, (physics noob), in my opinion, the inertia of the wheel shouldn't affect the exit velocity of the car at the bottom of the ramp by too much. So I think it would be better to use smaller wheels, which increase accuracy, rather than using the 2 3/8 in wheels. So what would be the advantages of using the 2 3/8 in wheels overusing the smaller like 1.5 in wheels?

Also, I tried doing some math, and the max time is 1.81 sec (starting at the top of the ramp). Starting .75 m above would cause the time to only decrease by around .281 sec (this is in the ideal world). The effect will probably be more prominent in the real world so let's just say .5 sec. How will making the CG to the front of the car differ the accuracy of the car? Would this only negatively affect skidding (which is positive)?

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Re: Gravity Vehicle C

Postby MadCow2357 » October 10th, 2019, 5:58 am

I was wondering what forces could make the car, while going down the ramp, move away from the surface of the ramp in the x-direction (if x was parallel to the ground)? I was thinking it could be the center of gravity of the car in the x-direction. In other words, the CG is too high above the car. Would this be a reason why my car does this?

Another question, (physics noob), in my opinion, the inertia of the wheel shouldn't affect the exit velocity of the car at the bottom of the ramp by too much. So I think it would be better to use smaller wheels, which increase accuracy, rather than using the 2 3/8 in wheels. So what would be the advantages of using the 2 3/8 in wheels overusing the smaller like 1.5 in wheels?

Also, I tried doing some math, and the max time is 1.81 sec (starting at the top of the ramp). Starting .75 m above would cause the time to only decrease by around .281 sec (this is in the ideal world). The effect will probably be more prominent in the real world so let's just say .5 sec. How will making the CG to the front of the car differ the accuracy of the car? Would this only negatively affect skidding (which is positive)?
Alright I'm a freshman so please don't hate on my bad physics, but I'll try to answer to the best of my abilities.

1. When you mean parallel to the ground, do you mean parallel to the direction of the track, or parallel to the width of the track? If you mean the latter, mass placement does indeed impact the "drift" towards the side. If you mean the former, it is possible that your CG is too high above the car. If it's too high, your car will have tendencies to "pop wheelies", so a little bit in front of the back axle should be the optimal mass placement. Mark Rober goes over this in his Pinewood Derby video.

2. Yes, I think you're correct in saying that smaller wheels will be beneficial. However, imo it's not for the "accuracy" - smaller wheels usually have less mass and therefore less rotational inertia. The heavier wheels are, the more force is required in order to get them spinning. However, if you think about it, smaller wheels will have to rotate more in order to travel the same distance, which makes the friction between the axles and the bearings/bushings a bigger factor. The accuracy you speak for a smaller wheel is pretty much irrelevant if you calibrate to fractions of a wheel rotation.

3. Can't really answer that one, it's way over my head :lol:
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