Braking

User avatar
MTV<=>Operator
Member
Member
Posts: 138
Joined: February 8th, 2019, 12:41 pm
Division: C
State: NY
Has thanked: 8 times
Been thanked: 4 times

Braking

Post by MTV<=>Operator » September 5th, 2019, 5:28 pm

In terms of braking, what type of system is everyone thinking about using? So far, since the vehicle has at least 0.5 meters to slow to a stop, I was thinking of using a wingnut system but with a spring to avoid skid.

On another note, how would one ensure that there is sufficient play between the wingnut and the threaded rod so as to avoid friction? Do you get a wingnut with a slightly larger ID than the diameter of the rod? Would using a plastic wingnut help reduce friction as well?

Sorry for all the questions, but I am trying to help our build coordinator compile a list of parts for a mass order for all 3 of our teams.
THHS '21 Builder Cult Member
2017-2018
2018-2019
2019-2020: GV (9 YUSO, 5 Regional), Detector (8 YUSO, 7 Regional), WS (10 Regional), PPP
2020-2021 Events/ Yosemite
Vehicle Design / 1
WICI / 3
Circuits /--
Machines /--

AngelMB
Member
Member
Posts: 16
Joined: June 3rd, 2018, 12:04 pm
Division: C
State: FL
Has thanked: 2 times
Been thanked: 0

Re: Braking

Post by AngelMB » September 5th, 2019, 10:09 pm

MTV<=>Operator wrote:
September 5th, 2019, 5:28 pm
In terms of braking, what type of system is everyone thinking about using? So far, since the vehicle has at least 0.5 meters to slow to a stop, I was thinking of using a wingnut system but with a spring to avoid skid.

On another note, how would one ensure that there is sufficient play between the wingnut and the threaded rod so as to avoid friction? Do you get a wingnut with a slightly larger ID than the diameter of the rod? Would using a plastic wingnut help reduce friction as well?

Sorry for all the questions, but I am trying to help our build coordinator compile a list of parts for a mass order for all 3 of our teams.
I'll be using a wingnut braking system as well, for my first vehicle at least. I don't believe using a larger ID than the diameter of the rod would work out well. Personally, I had problems with one of my MV last year where the wingnut was too big for my threaded rod and ending up sliding across the rod rather than travelling across its threads essentially making the brake useless. Also the pitch size of the wingnut and the rod may not line up leading to a nonfunctional brake.

I do like your idea of using a spring to try to slow down your vehicle after the 8.5 m mark. I had a similar idea for my vehicle and will probably end up using a spring for my first vehicle. You may wish to purchase a kit containing multiple springs of different sizes and spring constants seeing as you don't know exactly what you need to slow down. Your spring will need to be rigid to withstand constantly being expanded, but not too rigid as to take too much kinetic energy away from your vehicle. Remember, you still need to travel 0.5 - 3.5 meters past that 8.5 m mark and want to ensure you have enough momentum to make it all the way.

To reduce friction, I would suggest making sure your threaded rod is as straight as possible (try to limit the bending of this axle as it can lead to enormous amounts of friction if bent) and to ensure that the axle is clean. You may wish to lubricate your axle as well if friction does appear to be a problem there. I suggest using a relatively thicker (6-8 mm diameter) threaded rod to prevent the risk of bending, this is definitely doable seeing as there isn't nearly as much of a weight constraint as there was with MV last year.

As for plastic wingnuts, I don't have the most experience with them, but I don't imagine friction decreasing a significant amount by using plastic over metal, I may be wrong here though. I'm going to stick with metal wingnuts.
Boca High '20

2020 Events
Boomi, Circuits, Detector, Gravity

Nats Placements 2019
Mission - 1st
Circuits - 7th
Mousetrap - 23rd

iwonder
Admin Emeritus
Admin Emeritus
Posts: 1115
Joined: May 10th, 2011, 8:25 pm
Division: Grad
State: TX
Has thanked: 0
Been thanked: 0

Re: Braking

Post by iwonder » September 6th, 2019, 5:54 am

Some sort of light oil will help friction, and while threads do have different 'fits', going a size up won't help much. If it's too tight you could run a tap through the wingnut a few times and probably get it to fit a little more loose. If you go plastic you can 'break in' the wingnut by running it up and down the shaft a few times, but you'll probably need to replace it as it wear out.

Depending on how you use the springs they might bind in the threads of the rod. I've also seen teams use rubber washers to prevent the skidding.
'If you're the smartest person in the room, you're in the wrong room' - Unknown

User avatar
Unome
Moderator
Moderator
Posts: 4285
Joined: January 26th, 2014, 12:48 pm
Division: Grad
State: GA
Has thanked: 181 times
Been thanked: 59 times

Re: Braking

Post by Unome » September 6th, 2019, 10:17 am

iwonder wrote:
September 6th, 2019, 5:54 am
Some sort of light oil will help friction, and while threads do have different 'fits', going a size up won't help much. If it's too tight you could run a tap through the wingnut a few times and probably get it to fit a little more loose. If you go plastic you can 'break in' the wingnut by running it up and down the shaft a few times, but you'll probably need to replace it as it wear out.

Depending on how you use the springs they might bind in the threads of the rod. I've also seen teams use rubber washers to prevent the skidding.
Oh hey you're back!
Userpage
Chattahoochee High School Class of 2018
Georgia Tech Class of 2022

Opinions expressed on this site are not official; the only place for official rules changes and FAQs is soinc.org.

User avatar
CPScienceDude
Exalted Member
Exalted Member
Posts: 354
Joined: December 12th, 2018, 2:40 pm
Division: C
State: IN
Pronouns: He/Him/His
Has thanked: 139 times
Been thanked: 80 times

Re: Braking

Post by CPScienceDude » October 6th, 2019, 5:14 pm

This is my first time on a vehicle event, and I was wondering what the difference is between having the braking system on the front axle or back axle.
Captain of CPSO

Assassinator 139 and 147
2021 events: Astronomy, Chem Lab, Ornithology, Machines, Gravity Vehicle, and Forensics

About Me!
Image

knightmoves
Member
Member
Posts: 318
Joined: April 26th, 2018, 6:40 pm
Has thanked: 2 times
Been thanked: 27 times

Re: Braking

Post by knightmoves » October 7th, 2019, 12:11 pm

CPScienceDude wrote:
October 6th, 2019, 5:14 pm
This is my first time on a vehicle event, and I was wondering what the difference is between having the braking system on the front axle or back axle.
Do you own a bicycle? If you compare stopping with the front brake only and stopping with the rear brake only, what is the difference? Try it (somewhere safe!) and see.

When you brake, the friction of the tires against the floor applies a force in the backward direction, to slow you down. This force is beneath the center of mass of your car / bike, so you have a moment about the center of mass that tends to rotate the front of the vehicle downwards. That's why when you brake hard in a car / bike, it tends to want to stand up on its nose.

So as you brake, because of this turning moment, more of the car's weight is carried by the front wheels than by the back wheels. Assuming a constant coefficient of friction, that means you get more braking from the front wheel than the back wheel.

User avatar
CPScienceDude
Exalted Member
Exalted Member
Posts: 354
Joined: December 12th, 2018, 2:40 pm
Division: C
State: IN
Pronouns: He/Him/His
Has thanked: 139 times
Been thanked: 80 times

Re: Braking

Post by CPScienceDude » October 7th, 2019, 12:54 pm

knightmoves wrote:
October 7th, 2019, 12:11 pm
CPScienceDude wrote:
October 6th, 2019, 5:14 pm
This is my first time on a vehicle event, and I was wondering what the difference is between having the braking system on the front axle or back axle.
Do you own a bicycle? If you compare stopping with the front brake only and stopping with the rear brake only, what is the difference? Try it (somewhere safe!) and see.

When you brake, the friction of the tires against the floor applies a force in the backward direction, to slow you down. This force is beneath the center of mass of your car / bike, so you have a moment about the center of mass that tends to rotate the front of the vehicle downwards. That's why when you brake hard in a car / bike, it tends to want to stand up on its nose.

So as you brake, because of this turning moment, more of the car's weight is carried by the front wheels than by the back wheels. Assuming a constant coefficient of friction, that means you get more braking from the front wheel than the back wheel.
So, would it be more beneficial to have the breaking mechanism in the back because of how the timing works? Because, to me, it sounds like having the break in the front will cause for more sudden stop, and thus has more potential for skidding. Though, if you have it in the back, the front may drift, causing for the final stopping position of the car to be skewed. I may be way over analyzing this, but I just want to be sure I'm not making any rookie mistakes
Captain of CPSO

Assassinator 139 and 147
2021 events: Astronomy, Chem Lab, Ornithology, Machines, Gravity Vehicle, and Forensics

About Me!
Image

cool hand luke
Member
Member
Posts: 132
Joined: October 4th, 2016, 10:04 am
Division: B
State: TX
Has thanked: 0
Been thanked: 1 time

Re: Braking

Post by cool hand luke » October 7th, 2019, 2:31 pm

braking on a bike and braking on a car act very very differently if you lock up the rears. Bike - no problem. Car, "oh look there's the road behind me why am I looking backwards"

eatablechief21
Member
Member
Posts: 4
Joined: October 17th, 2019, 6:27 pm
Division: C
State: CA
Has thanked: 0
Been thanked: 0

Re: Braking

Post by eatablechief21 » October 17th, 2019, 6:34 pm

Can anyone give me some designs on how to build a wingnut braking mechanism. I'm new to the event and need a lot of help since I'm the only one doing it at our school :cry: .

User avatar
IvanGe
Member
Member
Posts: 199
Joined: September 29th, 2016, 1:56 pm
Division: C
State: NY
Has thanked: 0
Been thanked: 0

Re: Braking

Post by IvanGe » October 17th, 2019, 6:45 pm

eatablechief21 wrote:
October 17th, 2019, 6:34 pm
Can anyone give me some designs on how to build a wingnut braking mechanism. I'm new to the event and need a lot of help since I'm the only one doing it at our school :cry: .

Check out the scioly wiki page for Gravity Vehicle. There are some examples of braking systems on there. https://scioly.org/wiki/index.php/Gravity_Vehicle
gelinas 2016-2019, wmhs'22

nats '19:
5th - potions
5th - fossils
9th - buggy

Locked

Return to “Gravity Vehicle C”

Who is online

Users browsing this forum: No registered users and 1 guest