2011 design

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2011 design

Post  David Smith on Mon Oct 17, 2011 9:42 pm

If we were to redesign the robot based on what we know, lets look at some things.
1114 had to turn around to pick up the tub and hang it, we did not.

Our arm should have been faster, would it be possible and stay in the weight?
Arm is probably more vunerable to damage during the match.
More stress on arm focrum.

A fork lift allows you to be closer to the rack I think therefore driver input, left and right turns are less sensitive.
One motor for all the way up I think where we used two and now three.

mechanically, advantage forklift.
Weight I am not sure.
If our arm was faster and did not hunt the advantage would be arm
as to the game play.

Your comments please.


David Smith

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Re: 2011 design

Post  kenneth on Thu Oct 20, 2011 1:19 am

1114's forklift was close to the centre of mass of the robot so turning for them would not have caused much swaying. They could also do zero radius turns quickly and easily with a simple tank drive.
For our pivoting single bar arm, our speed is limited by a few factors:
-how much the arm jerks the robot when it pivots up fully
-how much precision we can achieve for the middle rack
-how much space we have to package our arm
Our current arm's speed can be increased by adding more counterbalance but dampening and accurate positioning becomes an issue. Another way to elevate the jerking would be to move the centre of mass of the robot closer to the front, but we dont have any spare weight to play with currently.

An advantage to the forklift is that its motion is always perpendicular to the motion of the robot and therefore have minimal effect on eachother's motion.

An simpler and lighter alternative to the forklift was done by 842:https://www.youtube.com/watch?v=cYP4pshmW3k
They had a virtual 4 bar linkage and it was the only one this year I am aware of. It is extremely simple with fewer moving parts and has less mass. This design doesnt really need dampening or alot of power to move because of its lack of weight.
This arm with a roller claw among other things would have been a competitive robot.

Also, using 2 joysticks to control the robot, especially the way they are currently spaced, is actually extremely awkward. 1114 and 2056 use corded ps3 or 360 controllers which are significantly more ergonomic and anthropometrically correct. The folding board everything is mounted to is also heavy and difficult to carry, 1114 carries a laptop and 2 controllers. On a ps3 or 360 controller there are 2 analog sticks, 2 analog triggers and 12 practical buttons to use compared to 2 joysticks and 10 practical buttons we can use with our current control scheme.
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Re: 2011 design

Post  David Smith on Thu Oct 20, 2011 10:47 pm

842 had a very interesting arm design.
Without seeing more it looks to me that there would need to be another pivot at the wrist to pick up off the floor and to stay in the start dimensions at the start.. Can this be evenly counter balanced through out the entire range of motion. I am not sure but I do not think so because there is not always the same amount of arm at all times on either side of the fulcrum. I am curious about the force needed to turn it and how it changes as it rotates. How even is it?

The main arm turns about 180 degrees where our arm turned about 130 degrees ( i'm guessing) which means we would need more power depending on how it is weighted and more speed.

Less position switches are needed.

Because it turns 180 a ram could not be used to act as a shock if needed.

Do you have more info on there final robot assembly.

Just looked at their web site. I saw some final pics. This design would not of given us the flexibility to try different mini bot launchers .

That is one major advantage the we had with all the space in the middle of the robot free.

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Re: 2011 design

Post  kenneth on Fri Oct 21, 2011 12:08 am

Their arm is the equivilent of a parallel 4 bar linkage, it would scribe a circle if they spin it 360 degrees, they dont need a wrist because of this, there is a good shot at about 1:50:
https://www.youtube.com/watch?v=VWtNLg6GpW4&feature=related

I dont think their motion would be as fluid as a forklift but the setup does weigh considerably less. Because it is a virtual 4-bar linkage it cannot be counterbalanced as far as I know. if we anted dampening we could use a rotary pneumatic actuator which was allowed this year:
http://www.fabco-air.com/pdf/rotary_web.pdf
Unfortunately they are heavy.

They might not have needed as much power because the mass of their claw was not extended out on a long arm like ours, their lengths looked to be about half as long. The motor driving 842's arm wouldnt necessarily need more power because of the difference in weight compared to ours.

The key advantage to their arm design was weight and simplicity.
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