High Speed Braking

dcambrid
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Re: High Speed Braking

Post by dcambrid » April 28th, 2016, 6:02 am

When you say motor braking are you just setting the speed to 0 or reversing the speed for a few ms? We saw something similar to what you describe, we used a loop to reduce the speed every 5ms/10ms down to zero and we noticed a slight turn to the left which looked like skidding. The only explanation I came up with was that our driving gear is on the left side of the axle and could be causing the left wheels to slow just slightly quicker than the right. From searching online I believe the term is Torque steering which you sometimes see in rear wheel drive vehicles. We also saw a similar curve the other direction when speeding up quickly. Now our vehicle is slower than yours (2.5/2.6 secs) and brushed so not sure if that helps any. In the end ours was very consistent so we just planned for it to happen and lined up our vehicle to compensate. If you are just suddenly going from top speed to 0 you will likely skid at the speed you are going. Have you tried a more gradual slow down? We found the controlled slow down to be the most consistent.

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Re: High Speed Braking

Post by windu34 » April 28th, 2016, 8:47 am

dcambrid wrote:When you say motor braking are you just setting the speed to 0 or reversing the speed for a few ms? We saw something similar to what you describe, we used a loop to reduce the speed every 5ms/10ms down to zero and we noticed a slight turn to the left which looked like skidding. The only explanation I came up with was that our driving gear is on the left side of the axle and could be causing the left wheels to slow just slightly quicker than the right. From searching online I believe the term is Torque steering which you sometimes see in rear wheel drive vehicles. We also saw a similar curve the other direction when speeding up quickly. Now our vehicle is slower than yours (2.5/2.6 secs) and brushed so not sure if that helps any. In the end ours was very consistent so we just planned for it to happen and lined up our vehicle to compensate. If you are just suddenly going from top speed to 0 you will likely skid at the speed you are going. Have you tried a more gradual slow down? We found the controlled slow down to be the most consistent.
Our vehicle travels backwards so we usually are accelerating right up to the 8.5m line and then brake. While it doesn't really matter how far our vehicle travels while braking, we don't know for sure that there will be an unobstructed path beyond the target point so we are trying to brake as quickly as possible and if needed, adjust the length of our acceleration if there is an obstruction. Our axle connecting the rear wheels is one solid piece (no differential) and the length/distances are equal. We are not skidding, I have adjusted the delay in the loop so that it does not skid as far as I can tell, but ill take another loop at it
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Re: High Speed Braking

Post by Bazinga+ » April 28th, 2016, 9:46 am

windu34 wrote:
dcambrid wrote:When you say motor braking are you just setting the speed to 0 or reversing the speed for a few ms? We saw something similar to what you describe, we used a loop to reduce the speed every 5ms/10ms down to zero and we noticed a slight turn to the left which looked like skidding. The only explanation I came up with was that our driving gear is on the left side of the axle and could be causing the left wheels to slow just slightly quicker than the right. From searching online I believe the term is Torque steering which you sometimes see in rear wheel drive vehicles. We also saw a similar curve the other direction when speeding up quickly. Now our vehicle is slower than yours (2.5/2.6 secs) and brushed so not sure if that helps any. In the end ours was very consistent so we just planned for it to happen and lined up our vehicle to compensate. If you are just suddenly going from top speed to 0 you will likely skid at the speed you are going. Have you tried a more gradual slow down? We found the controlled slow down to be the most consistent.
Our vehicle travels backwards so we usually are accelerating right up to the 8.5m line and then brake. While it doesn't really matter how far our vehicle travels while braking, we don't know for sure that there will be an unobstructed path beyond the target point so we are trying to brake as quickly as possible and if needed, adjust the length of our acceleration if there is an obstruction. Our axle connecting the rear wheels is one solid piece (no differential) and the length/distances are equal. We are not skidding, I have adjusted the delay in the loop so that it does not skid as far as I can tell, but ill take another loop at it
As I said before, if you start braking at 8.5 meters and you accelerate as fast as you can up to 8.5 meters, you will need exactly that distance to stop(so the best you can do is stop at 17 meters of you really are accelerating as fast as you can), and it seems like you are able to stop before 17 meters, so that means you could accelerate even faster. So I recommend accelerating faster for the first like 5 or 6 meters and decelerating right after.
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Re: High Speed Braking

Post by windu34 » April 28th, 2016, 7:22 pm

Bazinga+ wrote: As I said before, if you start braking at 8.5 meters and you accelerate as fast as you can up to 8.5 meters, you will need exactly that distance to stop(so the best you can do is stop at 17 meters of you really are accelerating as fast as you can), and it seems like you are able to stop before 17 meters, so that means you could accelerate even faster. So I recommend accelerating faster for the first like 5 or 6 meters and decelerating right after.
I figured it out today. I can brake in three meters without fishtailing coming right off a 1.5ish run
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