Vehicle Thickness

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Re: Vehicle Thickness

Postby invisiblebanana » March 15th, 2019, 1:47 pm

For those of you with 10-20 cm thick vehicles, isn't that too thin to implement a wingnut brake that can rewind to 12 meters?
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Re: Vehicle Thickness

Postby builder83 » March 15th, 2019, 6:54 pm

invisiblebanana wrote:For those of you with 10-20 cm thick vehicles, isn't that too thin to implement a wingnut brake that can rewind to 12 meters?


Quite easy unless your using like 2 inch diameter wheels. Use 4 inch wheels and you could probably make it 8cm! Really gets more the the question of losing accuracy left/right at some point. I saw quite a few cans smucked last week.

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Re: Vehicle Thickness

Postby MadCow2357 » March 15th, 2019, 7:05 pm

builder83 wrote:Quite easy unless your using like 2 inch diameter wheels. Use 4 inch wheels and you could probably make it 8cm! Really gets more the the question of losing accuracy left/right at some point. I saw quite a few cans smucked last week.

Wdym losing accuracy left/right?
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Re: Vehicle Thickness

Postby builder83 » March 15th, 2019, 8:15 pm

MadCow2357 wrote:
builder83 wrote:Quite easy unless your using like 2 inch diameter wheels. Use 4 inch wheels and you could probably make it 8cm! Really gets more the the question of losing accuracy left/right at some point. I saw quite a few cans smucked last week.

Wdym losing accuracy left/right?


Just meant that the narrower the buggy becomes the more an adjustment compounds its steering. You could build a battery motorcycle 3 cm wide but but good luck steering it! I didnt try a buggy under 10 cm though so I will differ to those who have tried. Anybody try anything ridiculously thin with any consistant accuracy?

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Re: Vehicle Thickness

Postby Tendan » March 16th, 2019, 9:18 am

invisiblebanana wrote:For those of you with 10-20 cm thick vehicles, isn't that too thin to implement a wingnut brake that can rewind to 12 meters?

We have our lead screw running from the back of the vehicle to the front. The motor drives the screw at the rear, and a pair of bevel gears join the lead screw to the front axle to drive the front wheels.

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Re: Vehicle Thickness

Postby SPP SciO » March 18th, 2019, 8:49 am

Tendan wrote:
invisiblebanana wrote:For those of you with 10-20 cm thick vehicles, isn't that too thin to implement a wingnut brake that can rewind to 12 meters?

We have our lead screw running from the back of the vehicle to the front. The motor drives the screw at the rear, and a pair of bevel gears join the lead screw to the front axle to drive the front wheels.


Image Something similar to this? My students showed me this, but it looks costly to invest in at this point in the season - that's a lot of parts that need to be perfectly compatible. They had originally tried building a narrower car early in the season, but ran into the same problem with running out of thread space for the wingnut on the longer runs. Part of the problem also was using a lead screw rather than a typical hardware store threaded rod; the different thread spacing had a noticeable effect.
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Re: Vehicle Thickness

Postby MadCow2357 » March 18th, 2019, 9:24 am

SPP SciO wrote:
Tendan wrote:
invisiblebanana wrote:For those of you with 10-20 cm thick vehicles, isn't that too thin to implement a wingnut brake that can rewind to 12 meters?

We have our lead screw running from the back of the vehicle to the front. The motor drives the screw at the rear, and a pair of bevel gears join the lead screw to the front axle to drive the front wheels.


Image Something similar to this? My students showed me this, but it looks costly to invest in at this point in the season - that's a lot of parts that need to be perfectly compatible. They had originally tried building a narrower car early in the season, but ran into the same problem with running out of thread space for the wingnut on the longer runs. Part of the problem also was using a lead screw rather than a typical hardware store threaded rod; the different thread spacing had a noticeable effect.

Oh c'mon! And I was really hoping I was the only one who thought of this...

Any reason why the two axles are connected?
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Re: Vehicle Thickness

Postby SPP SciO » March 18th, 2019, 11:48 am

MadCow2357 wrote:Oh c'mon! And I was really hoping I was the only one who thought of this...

Any reason why the two axles are connected?


That's not a diagram of an actual battery buggy, just a "design idea" picture you see when you check out bevel gears at servocity, so I'm not sure what function they were going for. I'd be interested to know how using the bevel gears to move the wingnut parallel to the overall direction of movement would play out. Those servocity gears are designed to fit the 1/4" D shafting, which would need to be modified to fit a typical 1/4" threaded rod. It would be able to trip a switch, but can it effectively lock up the wheels at the same time? Also, is it correct to assume that the gear ratio will change the linear distance traveled by the wingnut? That's interesting for accuracy purposes - maybe if the distance is "stretched out" to 2x as long as usual, it's easier to set the wingnut with a ruler, rather than counting rotations. I hope you experiment and keep us posted
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Re: Vehicle Thickness

Postby invisiblebanana » March 18th, 2019, 5:01 pm

SPP SciO wrote:
MadCow2357 wrote:Oh c'mon! And I was really hoping I was the only one who thought of this...

Any reason why the two axles are connected?


That's not a diagram of an actual battery buggy, just a "design idea" picture you see when you check out bevel gears at servocity, so I'm not sure what function they were going for. I'd be interested to know how using the bevel gears to move the wingnut parallel to the overall direction of movement would play out. Those servocity gears are designed to fit the 1/4" D shafting, which would need to be modified to fit a typical 1/4" threaded rod. It would be able to trip a switch, but can it effectively lock up the wheels at the same time? Also, is it correct to assume that the gear ratio will change the linear distance traveled by the wingnut? That's interesting for accuracy purposes - maybe if the distance is "stretched out" to 2x as long as usual, it's easier to set the wingnut with a ruler, rather than counting rotations. I hope you experiment and keep us posted


You could always use a 1:1 gear ratio for the bevel gear if you're concerned with accuracy.

My design also uses the ServoCity aluminum channel, and the wingnut brake locks up the wheels decently. Sometimes it pushes the wingnut into the ball bearing hub a little bit so the wheels don't really turn in any direction, but a little bit of force fixes it. The gears also fit my 1/4 in threaded rod perfectly, but idk about if it'll fit everyone's.

Madcow: Are you also using the ServoCity channel and bevel gears? And I guess the bevel gears are connected to ensure that the vehicle will completely stop moving once the wingnut locks up, but it seems a little unnecessary.

I think we'll see many designs like that at nats :)
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Re: Vehicle Thickness

Postby Tendan » March 18th, 2019, 6:02 pm

SPP SciO wrote:
Tendan wrote:We have our lead screw running from the back of the vehicle to the front. The motor drives the screw at the rear, and a pair of bevel gears join the lead screw to the front axle to drive the front wheels.


Image Something similar to this? My students showed me this, but it looks costly to invest in at this point in the season - that's a lot of parts that need to be perfectly compatible. They had originally tried building a narrower car early in the season, but ran into the same problem with running out of thread space for the wingnut on the longer runs. Part of the problem also was using a lead screw rather than a typical hardware store threaded rod; the different thread spacing had a noticeable effect.

Our setup is a bit simpler than that, but it's the same idea. The main differences are:
1. Our setup has the motor driving one pair of wheels, instead of the two pairs that the example would be powering.
2. We are using a 1:1 gear ratio.
3. Our support structure is made up of one solid 3D printed piece.
4. A lead screw runs between the motor and gears. It would sort of be where the long axle is in the picture.

The gears we found are on servocity for $30 for 2. If you have spare bearings and access to a 3D printer, you shouldn't have to buy much else to be able to replicate the idea in the photo without having to buy all of the structural parts and additional bearings. That being said, if your team doesn't have a member proficient in 3D modeling, it might be better to buy the support structure too.

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Re: Vehicle Thickness

Postby MadCow2357 » March 18th, 2019, 6:19 pm

invisiblebanana wrote:Madcow: Are you also using the ServoCity channel and bevel gears? And I guess the bevel gears are connected to ensure that the vehicle will completely stop moving once the wingnut locks up, but it seems a little unnecessary.

Might be, might not be... if we qualify, you'll see at nats. ;)
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Re: Vehicle Thickness

Postby invisiblebanana » March 18th, 2019, 6:23 pm

hmmm... :?:

I think that's a yes ;)
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Re: Vehicle Thickness

Postby MadCow2357 » March 18th, 2019, 8:01 pm

invisiblebanana wrote:hmmm... :?:

I think that's a yes ;)

#misleadingpeople ;)
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Re: Vehicle Thickness

Postby SPP SciO » April 8th, 2019, 10:14 am

Sharing this here (with student permission) in case it helps inspire anyone else. They ran on Saturday, and placed 37th - terrible! But a teachable moment!

https://drive.google.com/file/d/1MlfzGXuOg6gSrvnymvin_GnUOQNBbVMD/view?usp=sharing This picture captures the basic essence of their device - they wound up tacking on a piece of sponge to the brake switch, and hanging a 200g weight off the side of the chassis to cut down on the wild skidding.

https://drive.google.com/file/d/1BY-reu88SieJhl8Jeu3_GqXiWvfBKZnl/view?usp=sharing This is a video of the BB in action "as intended"

What really nailed them at competition was the dowel. Apparently, they took the dowel off to fit the car in their carry case, but when they reattached it, they used a screw in a different hole, meaning the dowel was no longer leading (slightly behind the front wheel). They took so much time trying to fix this issue and only got in one run during the 8 minutes. There was also too much space between the switch and the wingnut (too thick of a foam piece, or the switch shifted positions on them) so when the switch was activated, the wheels failed to lock, and the car just coasted to a stop far away from the target. 1300 points and tier 3 = 37th at NYSSO.

Major take-aways:
1. Don't start an ambitious re-design without enough time to work out all the bugs. "Don't practice until you get it right, practice until you can't get it wrong." If they had this bevel gear idea in the middle of November instead of the middle of March, there wouldn't have been so many band-aid fixes that piled up.
2. Don't get tiered. As a coach, I feel a little guilty - I could have easily done an impound walk-through with them and hopefully noticed the dowel situation. But, that was their job. Get someone else to objectively evaluate your vehicle for violations. I would hope at Nationals everyone will be Tier 1 though!
3. Remember that improving accuracy is worth more points than improving the gap. It wasn't very hard to hit the "gap ceiling" - they were pretty comfortable hitting a 30cm gap every time, and probably could have gone to 20cm with little risk. But, even if they had an additional month to test, I don't think the steering and distance calibrations were fine enough to reliably get closer than 20cm from the target.

Anyway - take it or leave it - this was just our experience from the weekend! I personally love this event, since it's the one that got me hooked on SciO back when I was a student competitor. Fun to do, fun to coach, and fun to watch! Good luck to everyone who still has at least one more BB run left this season!
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Re: Vehicle Thickness

Postby AugustW » April 12th, 2019, 8:25 pm

How do you get it less than 20cm. Do you use wingnut to stop, because I do, and that is the narrowest I can get it with having enough room for the wing nut to reach 12 meters distance. I used wingnut and counting revolutions. Do you have any other ideas of how to brake. Also, is there electric vehicle in high school? Still active?


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