High Speed Braking

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High Speed Braking

Post by windu34 » April 27th, 2016, 6:14 pm

I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
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Re: High Speed Braking

Post by Bazinga+ » April 27th, 2016, 6:53 pm

windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
You need the same amount of distance to accelerate as to deccelerate, and if these problems are only present during decceleration, then you just need to decrease the rate at which the vehicle slows down (ideally it should be speeding up half the travel, and slowing down the rest).
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Re: High Speed Braking

Post by HandsFreeCookieDunk » April 27th, 2016, 6:58 pm

windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
Someone else might have to correct me if I'm wrong, but I believe that fishtailing will only occur in rear wheel drive vehicles, so maybe you could turn your vehicle around and reverse the direction of the motor so it becomes front wheel drive.

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Re: High Speed Braking

Post by windu34 » April 27th, 2016, 7:09 pm

HandsFreeCookieDunk wrote:
windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
Someone else might have to correct me if I'm wrong, but I believe that fishtailing will only occur in rear wheel drive vehicles, so maybe you could turn your vehicle around and reverse the direction of the motor so it becomes front wheel drive.
I believe you are correct, but Id really rather not change my vehicle seeing as how nationals is rapidly approaching. I was actually considering a parachute-like apparatus controlled by a servo that could help slow the vehicle, but if there is something simpler to implement, Id rather take that route.
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Re: High Speed Braking

Post by windu34 » April 27th, 2016, 7:10 pm

Bazinga+ wrote:
windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
You need the same amount of distance to accelerate as to deccelerate, and if these problems are only present during decceleration, then you just need to decrease the rate at which the vehicle slows down (ideally it should be speeding up half the travel, and slowing down the rest).
Do I though? I feel like there should be a way to rapidly brake using a brake curve or changing the way/rate I apply the brake.
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Re: High Speed Braking

Post by Chris_L » April 27th, 2016, 7:16 pm

windu34 wrote:
Bazinga+ wrote:
windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
You need the same amount of distance to accelerate as to deccelerate, and if these problems are only present during decceleration, then you just need to decrease the rate at which the vehicle slows down (ideally it should be speeding up half the travel, and slowing down the rest).
Do I though? I feel like there should be a way to rapidly brake using a brake curve or changing the way/rate I apply the brake.
Why don't you make the rear wheel axle longer, making the vehicle wider? And then add more weight to the very back? That could solve ur problem of the back brake fishtailing? Maybe I'm wrong though but that's my intuition.
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Re: High Speed Braking

Post by Bazinga+ » April 27th, 2016, 7:19 pm

windu34 wrote:
Bazinga+ wrote:
windu34 wrote:I have been having some trouble with braking my vehicle. My run time is about 1.5s and I'm using a brushless setup. I have been having some trouble with the vehicle "fishtailing" and curving when the vehicle starts to decelerate. The vehicle brakes using the motor which is located in the rear. We have tried adding weight above the rear wheels, increasing the coefficient of friction between the wheels and the floor, as well as lowering the brake power, but all have not had a significant impact on the problem described. The vehicle travels straight during the acceleration period, it is only near the end of the braking that the vehicle experiences this effect. Any suggestions? Thanks
You need the same amount of distance to accelerate as to deccelerate, and if these problems are only present during decceleration, then you just need to decrease the rate at which the vehicle slows down (ideally it should be speeding up half the travel, and slowing down the rest).
Do I though? I feel like there should be a way to rapidly brake using a brake curve or changing the way/rate I apply the brake.
Nope. The maximum decelerating force is equal to the friction coefficient times the weight of the car pushing down in the wheels. It is physically impossible to decelerate more rapidly than that using the wheels. Not sure if you are still using a wingnut breaking system, but if you are, you will need to implement a spring break, so the car slows down continuously rather than immediately and completely. If you are using the motor to break, I advise to use timing to your advantage, and time it so the time it takes for the motor to get to full speed is the same as to get back to a complete stop. Other fixes won't( correction, shouldn't ) work since you are decelerating too fast.
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Re: High Speed Braking

Post by windu34 » April 27th, 2016, 7:33 pm

Bazinga+ wrote: Nope. The maximum decelerating force is equal to the friction coefficient times the weight of the car pushing down in the wheels. It is physically impossible to decelerate more rapidly than that using the wheels. Not sure if you are still using a wingnut breaking system, but if you are, you will need to implement a spring break, so the car slows down continuously rather than immediately and completely. If you are using the motor to break, I advise to use timing to your advantage, and time it so the time it takes for the motor to get to full speed is the same as to get back to a complete stop. Other fixes won't( correction, shouldn't ) work since you are decelerating too fast.
I am no longer using the wingnut braking system and am using the motor. If I were to do that, I would have to sacrifice my time score by at least .4 seconds which would result in 25% more points than I intend on scoring. There must be another way to do this that we have not thought of. Maybe a way to apply friction to the front axle during the braking time and keeping it friction-less during acceleration.
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Re: High Speed Braking

Post by windu34 » April 27th, 2016, 7:33 pm

Chris_L wrote:
Why don't you make the rear wheel axle longer, making the vehicle wider? And then add more weight to the very back? That could solve ur problem of the back brake fishtailing? Maybe I'm wrong though but that's my intuition.
How would making the rear wider help?
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Re: High Speed Braking

Post by Bazinga+ » April 27th, 2016, 7:54 pm

windu34 wrote:
Bazinga+ wrote: Nope. The maximum decelerating force is equal to the friction coefficient times the weight of the car pushing down in the wheels. It is physically impossible to decelerate more rapidly than that using the wheels. Not sure if you are still using a wingnut breaking system, but if you are, you will need to implement a spring break, so the car slows down continuously rather than immediately and completely. If you are using the motor to break, I advise to use timing to your advantage, and time it so the time it takes for the motor to get to full speed is the same as to get back to a complete stop. Other fixes won't( correction, shouldn't ) work since you are decelerating too fast.
I am no longer using the wingnut braking system and am using the motor. If I were to do that, I would have to sacrifice my time score by at least .4 seconds which would result in 25% more points than I intend on scoring. There must be another way to do this that we have not thought of. Maybe a way to apply friction to the front axle during the braking time and keeping it friction-less during acceleration.
It should be possible to fine tune your car so you have a solid break and don't sacrifice any time. Right now your car is more or less sliding to a stop, which is the maximum deceleration you can have. If you fine tune it so it degenerates just a bit less rapidly than it currently is you will have about the same time and improved accuracy. So just play around with the rate if breaking, and find the optimal balance between accuracy and speed.
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