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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.

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.

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.

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!

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.

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.

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

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"

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 .

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 .

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