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Unread 03-12-2003, 22:03
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Re: Top Speed

Hey, Brandon, can we give his mentors bad reputation via this post?
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Unread 03-12-2003, 22:47
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Re: Top Speed

Quote:
Originally Posted by M. Krass
Hey, Brandon, can we give his mentors bad reputation via this post?
DONT DO THAT!!!

They have a good reason, something about those acurrsed copyright/patent laws...
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Unread 05-12-2003, 18:35
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CVT ... I Disagree

This is the only subject to date that I somewhat disagree with Dr. Joe. Team 217 used the CCT in 2002 (see whitepapers) and, once it was working (I know we blew 2 regionals), was a definite advantage. I do agree, in part, with Joe on the cost aspects of the design and the initial risk, but the benefit is there along with the cool factor (I.E. Inspiration). I had never seen our students more excited than when the CCT went out on the field and worked. With the things we learned from the first year, I wouldn't be suprised if we used the CCT (refined, of coarse) again in 2004.

Having a CVT is not a "must have", but a "cool to have"

-Paul
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Unread 11-12-2003, 20:13
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Re: Top Speed

how does... 11 ft. per sec... with 416 lbs of torque per inch ... (on high).... and 4 ft. per sec.. with 960 lbs of torque per inch (on low) sounds... would you like to call that a fast bot with good torque?
  #35   Spotlight this post!  
Unread 11-12-2003, 21:53
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Re: Top Speed

One of the best ways that i use to evaluate speed is just to go out to a big, open space with a tape measurer, and measure out how far it goes in 10 seconds...it just sort of puts it in perspective
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Unread 11-12-2003, 23:25
Jay Lundy Jay Lundy is offline
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Re: Top Speed

We've been experimenting with a fast robot with an offset center wheel. We did it for the smaller turning radius (less resistance to turning), and we did it rather than the omniwheels because we were worried about being too easy to push sideways.

Anyway, it sure is fast, and with our transmission it can be fast and weak or slow and strong, but we have run in to one big problem: it is nearly impossible to control.

When we turn the robot, it only turns on the center wheels, and it flies at about 1 rev / s. That may sound good but it makes it impossible to control. Luckily they improved the controller this year, so we're working on a positioning system, most likely with the 300 deg / s gyro from Analog Devices (with increased range) and optical encoders on the wheels (at least, that's what I'd like to do).

If we can get it working, I'm hoping to create a control system where the driver pushes the joystick in a certain direction and the robot turns to that same orientation and drives forward with a speed proportional to the joystick's distance from center. We may also experiment with other ways of driving.

Basically, my point is: speed is good, but make sure you design something that can be controlled by a human.
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Unread 12-12-2003, 10:10
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Re: Top Speed

Quote:
Originally Posted by Jay Lundy

When we turn the robot, it only turns on the center wheels, and it flies at about 1 rev / s. That may sound good but it makes it impossible to control. Luckily they improved the controller this year, so we're working on a positioning system, most likely with the 300 deg / s gyro from Analog Devices (with increased range) and optical encoders on the wheels (at least, that's what I'd like to do).
Hmm...does it only turn on the center wheel?
If it was able to steer using the other four, i would recommend that the center wheel be used for quick turns ie. push a button and you get an immidiate 90* turn left or right. But if you could get it so that it steers the way you describe, it should be pretty neat. I think that i know a trig equation that could help you out, but i dont know if it would work with the "C" language(im a pbasic kind of guy).
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Unread 12-12-2003, 17:07
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Re: Top Speed

I would try closing the steering loop with the yaw rate sensor that FIRST supplies - It may seem slow, but you very seldom need to spin your bot around quickly

and the fact that your bot can turn that quickly, means you have a lot of gain available, which will allow you to close the loop with the yaw rate sensor and have the response be very tight

this is one of those concepts that are hard to explain - to be very accurate and precise, you system needs to be powerful - more powerfull than necessary for the task you are trying to perform

then you can use a large amount of negative feedback, and the response will be quick to your commands - not that it will turn quickly, but that it will quickly do exactly what you are commanding it to do.

so if you move the stick slightly, and want the bot to turn very slowly, it will immediately begin to turn very slowly, and it will continue to move very slowly at the same precise speed, no matter what gets in its way (other bots, obsticals)

to put it another way, you must have great strength in order to be gentle.
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Unread 13-12-2003, 23:17
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Re: Top Speed

Quote:
Originally Posted by Raul
I will say that if we decided to use more powerful motors (the Chips instead of the FP’s) then we could bump up our top speed accordingly. This is why 25’s Evil Machine, which used 6 motors for their drive, was effective at a higher top end speed. But yeah, at those speeds, the drive control sensitivity is very high and thus difficult to control the robot.

Raul
Acctually Raul, team 25 only used 4 motors for our drive, like alot of other teams, we used the Drills in conjunction with CIMs, it was our gearbox that gave us the higher speeds..... who knows what could happen next year

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Unread 14-12-2003, 00:07
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Re: Top Speed

Hmm. We just stick with what we know. We didn't have very good tools at our disposal...
Anyway, Last year we used the 2 Cims at an 18:1 ratio on a chain system with tank style drive and it worked great. We had a final top speed of about 8.5 - 9fps and I can't remember the torque exactly, but we had no problems pushing bots around. In fact during one of our final matches, we spent the whole time taking 435 (RoboDogs) virtually out of the match by pushing them around. It was cool.
I think the CIMs 18:1 at 40A is a good balance between speed and torque for a stable system. Throw in the strength of chain drive and a good chassis, and you've got a pretty good drive.
We've redesigned the drive a bit and plan to use the modified design this season. (So scouts, you already know what to expect for our upcoming drive !)
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Unread 14-12-2003, 02:30
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Re: Top Speed

Quote:
Originally Posted by Sachiel7
I think the CIMs 18:1 at 40A is a good balance between speed and torque for a stable system. Throw in the strength of chain drive and a good chassis, and you've got a pretty good drive.
Just a heads up for future posting for everyone (not picking on ya Sachiel):

ALWAYS POST WHEEL DIAMETER! 18:1 with a 4" diameter wheel is totally different than with 8" diameter. (Even a one inch difference can be up to a 25% different gear ratio!)

And with all due respect to Sachiel, I'll disagree and refer to my previous thoughts that you can't be both competitively* quick and strong with only one pair of motors and a single speed transmission. Though it might be a good balance, max pushing force or max speed must have compromised in that design.

Matt


* I definite competitive as a max speed greater than 10 feet per second, and having a maximum applied force of 150 lbs.
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Unread 14-12-2003, 13:02
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Re: Top Speed

well actually you can be effective if you are quick, and dont have a low gear ratio

if you work out the physics, when you get your bot moving fast and ram another bot, you apply far more force and energy than you could by trying to push them, no matter how much you gear down or how much traction you have

need a simple example? take a common nail and try to push it into a 2x4 with a hammer - push on it as hard as you want

the lift the hammer a few inches and tap the hammer on the head of the nail -it doenst take much energy at all cause you are storing up kinetic enegy as the hammer speeds up, and releasing it ALL on the impact.
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Unread 14-12-2003, 14:01
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Re: Top Speed

Sorry about that. We used 8" wheels.
We didn't really use impact force for our pushing. We pushed bots from a low impact speed. I'm sure it helped, but it wasn't our "source of force".

In my defense,
My big thing is you have bots out there with 2 speed transmissions that shift from 5 fps to 35fps. In what sense do you need all that speed? Even if it was 10fps, you're planning on clearing the field in less than 6 seconds? I do understand the need for speed, but I think there is a line somewhere in there.
If you can find a good balance between torque and speed then I usually stick with it. We didn't sacrifice much torue in that design, I'm trying to dig up our spec sheet to put some numbers up. But we had just enough speed and torque we needed to get the job done. Isn't that the key?
I can understand teams who think having a torque and speed shifting transmission would be good. It can be, but why slam the drive with more torque needed than the task requires? Why give it so much speed when it doesn't need it?
I like youre definition of a competitive drive train. I pretty much agree with it. Although, depending upon which region you're coming from, things might be different. In our region (VA) most bots top speed was 7fps or less. They were also running off of drills or lesser equivalent. So, we topped them with our speed without shifting, and their torque, apparently.
Our key is just to maintain the KISS principle; if we have a drive that has the speed and torque we require for our tasks, why take it over the edge?
Also, remember, we wouldn't be able to construct a shifting transmission if we wanted to anyway, as our resources have been very low.
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Unread 16-12-2003, 22:10
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Re: Top Speed

Quote:
Originally Posted by KenWittlief
another scientist, Giordano Bruno, was burned at the stake, for asserting space was infinite, and that other suns and solar systems, and earth like planets existed.
Some folks say that "space" is finite but unbounded (like the surface of a sphere is finite yet unbounded as a 2D analog). I was just thinking that poor Bruno may have toasted for nothing.

Probably off topice but that hit me as funny.
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