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Unread 27-12-2010, 21:55
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Re: Hypothetical Situation - Stairs

1. The wheels you speak of are probably the 8" AndyMark wheels, either the FIRST, FIRST slick, Plaction, etc. and the 8" IFI wheels

2. The IFI wheels use the same tread as the AndyMark Plaction wheels (Actually, they can use either, the difference is minor between wedgetop and roughtop, and you can get both from AndyMark or IFI, but the Roughtop tends to have more usable life).

3. Why not just use 8 Plaction wheels (or other wheels with roughtop tread) in a dropped center 8wd?
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Unread 27-12-2010, 22:16
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Smile Re: Hypothetical Situation - Stairs

Also, keep in mind, that you could modify some snowmobile treads. Team 1091 did that, last season, and we had some excellent success with traction and manueverability. We could easily navigate over the bumps, and by gearing down, we lost some speed, but we weren't pushed around.
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Unread 27-12-2010, 22:18
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Re: Hypothetical Situation - Stairs

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Originally Posted by Karthik View Post

In 2006, our use of tank treads had very little to do with climbing the ramps that were on the field. We went with the treads because we felt we could get more traction by taking advantage of the longer contact patch between the tread and the carpet. Granted, this does seem a bit odd considering the equation for traction has no surface area component. When you're dealing with two surfaces that interlock in the way carpet and roughtop tread do, the traditional model for evaluating traction doesn't exactly apply. Regardless, we chose treads because we wanted that robot to be immovable, the benefit of climbing the ramp was an added bonus. Again, the complexity, maintenance and cost could not have been justified just for climbing when a much simpler solution could have sufficed.
Did you have any issues with the tank treads coming off while in use or have suggestions that you guys used? I noticed that is was a common issue for team 195 and during a few drive train lessons have heard that treads have problem staying on track. Your 1114, 1503, and 1680's robots are some of the top tread robots in my honest opinion.
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Unread 27-12-2010, 22:34
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Re: Hypothetical Situation - Stairs

I have a question: what kind of legal servos are able to support a 100+ lb robot? Would pneumatics or other parts be necessary to support such a robot?
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Unread 27-12-2010, 22:41
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Re: Hypothetical Situation - Stairs

Go go gadget Packbot?
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Unread 27-12-2010, 22:41
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Re: Hypothetical Situation - Stairs

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Originally Posted by davidthefat View Post
I have a question: what kind of legal servos are able to support a 100+ lb robot? Would pneumatics or other parts be necessary to support such a robot?
I don't understand your question. What kind of application are you using to use them in? Which robot are you referring to?
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Unread 27-12-2010, 23:11
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Re: Hypothetical Situation - Stairs

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Originally Posted by davidthefat View Post
I have a question: what kind of legal servos are able to support a 100+ lb robot? Would pneumatics or other parts be necessary to support such a robot?
The Answer:

ANY

If you gear it enough


But id be faster if you used a more powerful motor such as a CIM or Fisher-Price.
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Unread 27-12-2010, 23:18
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Re: Hypothetical Situation - Stairs

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Originally Posted by davidthefat View Post
I have a question: what kind of legal servos are able to support a 100+ lb robot? Would pneumatics or other parts be necessary to support such a robot?
Perhaps a gearbox, geared for torque, with an encoder on the output. You could use a P loop to control the position.

You could use a ratchet device to support the robot most of the time, only releasing it when you want to change postion.
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Unread 27-12-2010, 23:31
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Re: Hypothetical Situation - Stairs

Or a worm gear. That would probably provide all of the reduction you would need.

I would probably mix a pair of encoders, a gyro (maybe) and an inclinometer. The encoders would determine wheel speed and distance, the gyro would (as usual) determine rotational velocity (Although you might have to do some stuff to keep it sensing correctly, or just use it when in a known orientation), and the inclinometer would detect the ground. An accelerometer *might* work but would be affected by the robot's forward velocity. A weight on a pot would work as well, but would have weight to it (and weight is always a bad thing).


David - about servos - They are weak motors with built-in logic to steer to a certain position, and work the same as a motor, Victor, and pot. Except they are weak. With a CIM or Fisher-Price as the motor, you have significantly more power, which with gearing means you can drive whatever load you must drive faster. Any motor can move the load, but a more powerful (not necessarily a higher/lower free speed or stall torque, but output power, measured in Watts) motor can perform the task faster.
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Unread 28-12-2010, 14:49
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Re: Hypothetical Situation - Stairs

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Originally Posted by BrendanB View Post
Did you have any issues with the tank treads coming off while in use or have suggestions that you guys used? I noticed that is was a common issue for team 195 and during a few drive train lessons have heard that treads have problem staying on track. Your 1114, 1503, and 1680's robots are some of the top tread robots in my honest opinion.
We had issues beyond belief. We were throwing treads all over the place. Most of the time we were snapping them rather than just having them fall off. This post discusses the issues a bit:

http://www.chiefdelphi.com/forums/sh...94&postcount=5

My the end of the season we had the belt trapped so it couldn't find a way to slide off. Unfortunately this really cut down our efficiency so our robot was slower than we hoped. Definitely not an ideal situation.
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Unread 28-12-2010, 15:26
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Re: Hypothetical Situation - Stairs

In 2004 we happened upon a simple, robust, and fast method for climbing the stair. We put drop down ramps made of UHMW plastic on the front of the robot and had 4 large knobby pneumatic tires. The ramps would start the match folded up and would drop down and latch into place, giving the front face of the robot a sloped leading edge that would be just above the top of the step, sort of like an amphibious car.

To climb the stair the driver would simple turn the robot to face the stair and apply throttle. The ramps would lift the nose and when the front tire hit the stair’s edge it would climb onto it. Because the robot would high center between the wheels, we put UHMW plastic strips on the frame so we could glide across until the rear wheels would engage. To get down from the platform we would just drive off and bounce a bit. It was not a finesse move and required the robot to tip about 30-45 degrees, so you needed a relatively low CG. I don’t think we ever tried, but I think we could have climbed multiple stairs if there was a good edge to bite into like in 2004.

This method served us very well and was very KISS, perhaps the KISSiest

Jay
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Unread 27-12-2010, 18:22
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Re: Hypothetical Situation - Stairs

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Originally Posted by Teched3 View Post
If I remember the game correctly, WPI (Team 190) had a great platform climber, went around a goal obstruction, and hung on a bar, all autonomously. Can't wait to see the new game. Speculation is generally fruitless, but can be fun for some.
The 190 robot also had across it, 4 sets of wheels, instead of just two. As it climbed up, parts of the robot were over hanging off the platform, and the robot could be supported by wheels in the center of the robot.

Also, this design worked well when it was able to get up on the platform in auto. I saw a few matches they were in where they did not make it up onto the platform. This posed a problem, as the robot could not turn well.

Just remember, many great designs have also had a major drawback.

A perfect example of this is finals match 2 from the championship of 2002. SPAM 180 beat 71 to the center goal, and knocked them out of the way. Without the goals secured to itself, not all that much they could do. http://www.thebluealliance.net/tbatv/match/2002cmp_f1m2

Not to move this off topic, but just remember there are always tradeoffs to be made. How you deal with the game elements and field is up to you.
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Unread 28-12-2010, 12:56
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Re: Hypothetical Situation - Stairs

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Originally Posted by Dave Scheck View Post
Check out our Encore promo video from that year to see more details.

Again, that was a different challenge with only a single step to deal with.
This is in my top 5 FRC Promo videos, I show this to students everytime they even think about making a promo video !
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Unread 27-12-2010, 14:16
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Re: Hypothetical Situation - Stairs

I'd probably approach the 6" stairs with a tank tread design as well. Perhaps only to climb - wheels could provide the regular movement.
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Unread 27-12-2010, 14:39
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Re: Hypothetical Situation - Stairs

A very fast and exciting way would be for a robot that had the ability to shift is CG very high (approximatley 3feet or higher), and then take a run at the platform and let the physics of momentum do the work.
Of course this strategy could literally turn into a trainwreck...
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