Competitive Times for Nationals

[jcmarcus0816]

Thats a combination of time and accuracy. The time score is the time in seconds multiplied by 2. The accuracy score is the distance from the target point in cm multiplied by 4. The total score is the sum of both values, and a bonus of -25 points if you make centerline bonus.

We are discussing time score, so I was essentially asking if anyone has seen cars that cover the distance in 2 seconds or less.

Would be sheer luck to have a 2 second car be sub 2 cm accuracy. Not to peel out the car would need to be heavy, and then there would be big skid issues.

That's not true at all whatsoever. If you have a heavy car with a consistent braking system, it is definitely possible to avoid skid issues as well.
NOTE: This is just my theory, as I am sure that if I really wanted to, I could push my times down.

Actually with a more massive car it would skid more. Think about inertia, that is directly related to mass, if something has no mass it should stop instantly so to reduce skidding you need to reduce inertia or mass.

[jcmarcus0816]

Addionally, weight does NOT result in skid issues. It may increase momentum, but it also increases normal force and I found that I could control skid quite well despite the heavy device (2-3 kg's). There are plenty of little things such as cleaning the floor, "conditioning" you tires, and adjusting weight distribution that can have large effects on reducing skid.

I'll definitely bring a Swiffer then ! I was told today by the high school coach that weight does not increase skid. He said that the heavier a vehicle was, the less skid there would be. Is that true? Also, how do you "condition" your wheels?

I don't think that is right, like I said im my last post the more mass you have the more inertia and the harder it is to stop, thus it skids more.
To reduce skidding you really need to increase the time the car takes to stop or decrease the speed.

[MadCow2357]

Addionally, weight does NOT result in skid issues. It may increase momentum, but it also increases normal force and I found that I could control skid quite well despite the heavy device (2-3 kg's). There are plenty of little things such as cleaning the floor, "conditioning" you tires, and adjusting weight distribution that can have large effects on reducing skid.

I'll definitely bring a Swiffer then ! I was told today by the high school coach that weight does not increase skid. He said that the heavier a vehicle was, the less skid there would be. Is that true? Also, how do you "condition" your wheels?

I don't think that is right, like I said im my last post the more mass you have the more inertia and the harder it is to stop, thus it skids more.
To reduce skidding you really need to increase the time the car takes to stop or decrease the speed.

Yeah I think the same thing. I am building a CF and 3D printed battery buggy that will be a lot lighter. I can always add weight later, so...

[shrewdPanther46]

My partner and I have had similar experience with windu's perspective... with a heavier car its skidding less

imo, i think it has more to do with the distribution rather than the total mass.

Define the chances of skidding as the distance required to brake (because if anyone really wanted to, they could always brake way earlier obv)

so lets do some quick maths
W=E
F*D=1/2*m*v^2
μ*mg*D=1/2*m*v^2

As you can see, the work required to stop the vehicle as well as the braking force that can be applied vary directly with the mass of the vehicle, so in theory, it would just cancel out and mass would not play a role.

HOWEVER, this is with disregard to the acceleration of the car at the beginning. Now, one may argue that the power to weight ratio on lighter cars will allow it to accelerate quicker than a heavier car. Its just Newton's second law. Yet, there is a necessity for a significant downforce on our cars as they are really light for the speeds they are moving at, and thus, the grip advantage provided by distributing weight on the drive axle will provide that downforce needed to accelerate efficiently. Its all about balance

But at the same time, on such a small scale, none of this really matters imo. But more mass is certainly safer, because with that downforce, your chances of skidding are less even if your speed is decreasing (especially with varying coeff. of friction on different floors, you never know)

So, I would just go with personal experience and experiment stuff that works well for your car

[shrewdPanther46]

Sorry for double posting.

I'll definitely bring a Swiffer then ! I was told today by the high school coach that weight does not increase skid. He said that the heavier a vehicle was, the less skid there would be. Is that true? Also, how do you "condition" your wheels?

I don't think that is right, like I said im my last post the more mass you have the more inertia and the harder it is to stop, thus it skids more.
To reduce skidding you really need to increase the time the car takes to stop or decrease the speed.

Yeah I think the same thing. I am building a CF and 3D printed battery buggy that will be a lot lighter. I can always add weight later, so...

Yes, you are going to have to add weight to it just as a heads up. I also suggest you work with your old car and play with the distribution on the back of your car (which is bouncing up and down or something lol). You need more downforce/traction. Put weight on it and just give it a try. It will be very, very difficult for you (or anyone for that matter) to fully construct and test a CF and 3d printed buggy starting 2.5 weeks ish before a big competition..

[MadCow2357]

Sorry for double posting.

I don't think that is right, like I said im my last post the more mass you have the more inertia and the harder it is to stop, thus it skids more.
To reduce skidding you really need to increase the time the car takes to stop or decrease the speed.

Yeah I think the same thing. I am building a CF and 3D printed battery buggy that will be a lot lighter. I can always add weight later, so...

Yes, you are going to have to add weight to it just as a heads up. I also suggest you work with your old car and play with the distribution on the back of your car (which is bouncing up and down or something lol). You need more downforce/traction. Put weight on it and just give it a try. It will be very, very difficult for you (or anyone for that matter) to fully construct and test a CF and 3d printed buggy starting 2.5 weeks ish before a big competition..

I have all of the CAD files done, and all of the parts have came in. I might not get too much testing done, but I'll try I guess.

[builder83]

Comparing a heavier electric vehicle brake system to battery buggy is a moot point. Remember that they could take their sweet time braking well past the target point (to reduce skid) and back up.

[shrewdPanther46]

Comparing a heavier electric vehicle brake system to battery buggy is a moot point. Remember that they could take their sweet time braking well past the target point (to reduce skid) and back up.

We can always brake earlier too, it is just that we would be paying the price of time instead, so i dont understand your point.

[windu34]

Also, reading back, I am pretty sure conditioning wheels is analogous to just cleaning them so there isnt a lot of dirt on them.

No Im not just referring to cleaning them. I used belt conditioner https://www.amazon.com/CRC-05350-Belt-C ... B000M8PZB4 which actually softened the wheels and dramatically increased friction for ~3-4 minutes after each application.

Comparing a heavier electric vehicle brake system to battery buggy is a moot point. Remember that they could take their sweet time braking well past the target point (to reduce skid) and back up.

This is true, however there were VERY FEW teams at nationals that did this and I am pretty certain 1st, 3rd, and 6th did NOT back up and I think Solon (4th?) also did not.

[shrewdPanther46]

What are your thoughts on my mass theory windu34? I recall there were similar discussions in the past. I'm curious to see what you think