Electric Vehicle C

[bearasauras]

Does this seem really obvious to everyone? I just received a response from SOINC, and it basically said that it was a stupid question because the rules are clear, without actually clarifying which of the two meanings was correct. Am I just being stupid, or is it reasonable to think that "leading" could be interpreted as "furthest down the track" rather than "front of the vehicle"?

In general, yes I think it's pretty obvious. Leading means the front relative to the direction of motion.

Assume a car was aiming at the target point in a way that was traditional last year which would have the dowel rod in front and the direction of motion. But if leading means, as Chalker writes, front relative direction to motion would it be a construction violation if a car placed like this was able to slide to the left or right since the dowel road would not be in the front of the car in that left/right direction of motion?

The FAQ and answer was just posted here

Q: How is "leading part of the vehicle" defined? Is it the forward-most part in the direction of the vehicle's travel or the closest part to the Target Point?
A: The "leading part of the vehicle" is the forward-most part in the direction of the vehicle's travel.

[windu34]

I've hit a road bump in my idea for dynamic steering. Has anyone has success with using a servo to steer off the centerline and return while retaining millimeter precision? What are your thoughts on top 6 at Nats scores? Is fixed steering the way to go?

[HandsFreeCookieDunk]

I've hit a road bump in my idea for dynamic steering. Has anyone has success with using a servo to steer off the centerline and return while retaining millimeter precision? What are your thoughts on top 6 at Nats scores? Is fixed steering the way to go?

I too have had precision issues with dynamic steering (although I just have my two drive wheels on separate motors). That being said, fixed steering has its own issues of having to align both the axle and the vehicle itself to particular angles at the competition whereas with dynamic steering you can at least program that stuff ahead of time.

I'm on a fairly new team, so I don't think I'm qualified to talk about Nat-level EVs.

[laidlawe18]

The experience that I have with servos which is from robot arm, is that they are good for applications like that where you twist a knob until you see that the servo has moved far enough. In EV, there's no human feedback loop and I don't think you'd get nearly the level of precision required. That said, a stepper motor is probably what you're looking for, because they can go to and maintain angles to the precision of ~0.1 degrees.

[Bazinga+]

The problem with stepper motors is they don't have absolute position. What I mean by that is once you turn the vehicle off and back on you can't reproduce a previous position since all positions are relative to the position of the stepper motor. As for servos, I definately agree that they are not precise enough. I calculated that you need about .1 mm precision on how you move the axle which is beyond what a servo can achieve consistently and reproduce well. I believe fixed steering is the best option and have had a lot of success with that after coming up with a very nice steering mechanism. I definately recommend thinking about good mechanical steering designs, which is what i believe will be most prevalent at nationals.

[RJohnson]

One way to overcome the absolute position problem with stepper motors is to create a physical stop (straight forward would probably work best) and then always reset the robot to that stop before the stepper motor changes the angle.

With regards to HandsFreeCookieDunk, I think that the fastest vehicles, with the bonus, will need to be aligned to specific angles at the competition irrelevant of whether or not the steering is dynamic or static. If you start straight ahead, you have to take a longer path, turning more steeply to get through the cans, so it'll slow you down. So for a Nats level EV, I think it's more about whether or not a motorized steering system can get you there more accurately than manually adjustable steering.

[windu34]

Ive been trying to use a digital brushless servo (very high quality) and feed it signals in the microsecond format in order to get more precision, but it has to be completely in sync with the encoder I am using to measure distance if I want the vehicle to end up exactly where it started (on the centerline). I have one motor controlling rear wheels and the servo is at the front to control steering. I might try to implement a fixed steering system using gears and a high resolution encoder to give me the angle precise to the thousandth's degree instead of my dynamic system because I wont have to worry about receiving interrupts from the distance encoder and attempting to sync with the servo position thus making things much easier. I don't think building a good fixed system is difficult, I'm more so worried about lining it up with the target at competition.
How are you guys aiming your vehicle?

[Bazinga+]

Ive been trying to use a digital brushless servo (very high quality) and feed it signals in the microsecond format in order to get more precision, but it has to be completely in sync with the encoder I am using to measure distance if I want the vehicle to end up exactly where it started (on the centerline). I have one motor controlling rear wheels and the servo is at the front to control steering. I might try to implement a fixed steering system using gears and a high resolution encoder to give me the angle precise to the thousandth's degree instead of my dynamic system because I wont have to worry about receiving interrupts from the distance encoder and attempting to sync with the servo position thus making things much easier. I don't think building a good fixed system is difficult, I'm more so worried about lining it up with the target at competition.
How are you guys aiming your vehicle?

I use a Lazer and a target with a line on it. The car needs to be aimed towards a point 2x the distance from the centerline to center of cans so we place the target there and direct the laser towards it. I've used scopes and sights on the past but laser is much more accurate and reproducible.

[Private Wang Fire]

Ive been trying to use a digital brushless servo (very high quality) and feed it signals in the microsecond format in order to get more precision, but it has to be completely in sync with the encoder I am using to measure distance if I want the vehicle to end up exactly where it started (on the centerline). I have one motor controlling rear wheels and the servo is at the front to control steering. I might try to implement a fixed steering system using gears and a high resolution encoder to give me the angle precise to the thousandth's degree instead of my dynamic system because I wont have to worry about receiving interrupts from the distance encoder and attempting to sync with the servo position thus making things much easier. I don't think building a good fixed system is difficult, I'm more so worried about lining it up with the target at competition.
How are you guys aiming your vehicle?

How do you think the fixed system can be made precise enough? I did some math and it seems as if your angle needs to be <.5 the adjust between even the regional distances. I know you can get the angle precisely with the encoder but wouldn't this be small enough to have every run messed up due to mechanical error with your vehicle? 0.5 degrees offset is a close estimate the difference between 0.5m distance increments w/ max wheelbase.

[Bazinga+]

Ive been trying to use a digital brushless servo (very high quality) and feed it signals in the microsecond format in order to get more precision, but it has to be completely in sync with the encoder I am using to measure distance if I want the vehicle to end up exactly where it started (on the centerline). I have one motor controlling rear wheels and the servo is at the front to control steering. I might try to implement a fixed steering system using gears and a high resolution encoder to give me the angle precise to the thousandth's degree instead of my dynamic system because I wont have to worry about receiving interrupts from the distance encoder and attempting to sync with the servo position thus making things much easier. I don't think building a good fixed system is difficult, I'm more so worried about lining it up with the target at competition.
How are you guys aiming your vehicle?

How do you think the fixed system can be made precise enough? I did some math and it seems as if your angle needs to be <.5 the adjust between even the regional distances. I know you can get the angle precisely with the encoder but wouldn't this be small enough to have every run messed up due to mechanical error with your vehicle? 0.5 degrees offset is a close estimate the difference between 0.5m distance increments w/ max wheelbase.

For the record, the system I use (fixed steering) allows me <.01 degree precision, and have been successful with it, so fixed steering is certainly viable.