pic: Team 2980 Open Source Robot

[eedoga]

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[Chris is me]

This looks neat. Are you building this for 2013, or as an off season thing?

I'm a little confused as to why there is both a tri-wheel and articulating system. Don't they both accomplish the same thing?

[Nuttyman54]

Originally Posted by Chris is me

This looks neat. Are you building this for 2013, or as an off season thing?

I'm a little confused as to why there is both a tri-wheel and articulating system. Don't they both accomplish the same thing?

This is part of their 2013 climbing mechanism. If I understand correctly, the wheels ride on either side of the corner pipe, allowing the robot to "drive" up it. The tri-wheels are used to get over the rung vertices sticking out. If you look at the geometry of how tri-wheels work, a suspension system is necessary to keep the wheel(s) in contact with the driving surface at the same distance apart during the transition.

[eedoga]

I think part of the issue is that you are not seeing the whole picture.


The robot has two of the system you are looking at at a 90 degree angle to eachother with the wheels coming together in a V-shape. The bottom of the v is where the pole is of the corner of the pyramid hopefully will be. It is our hope that as the robot drives up the pole the wheels will sort of grip the pole. with the original design the triwheels were meant to rotate around the cross beams. We realized shortly after we selected this design that the triwheels would bind up as soon as they came to an obstacle and tried to rotate because the arm length is longer when the wheels rotate down then when the wheels are flat. So...we came up with the idea of having the wheels on articulating arms so that they can move up and out allowing them to rotate around. In this way we hope to drive over the cross beams and have the wheels rotate around them.

It is our hope that articulating the wheels will also allow the wheels to drive over the cross beams without tilting the robot over backwards.

Fingers crossed. :-)

Hope this helps clear things up a bit.

Edoga

[Jeffy]

I very much like this idea, but every time I toyed with it I ran into one issue.

Traction. How do you plan to stay "glued" to the diagonal pole? It would seem that without both a radical CG and SUPER sticky material, it is not possible to get up at a 60 degree angle. What are you using to increase frictional force on the poles?

edit:
Found the answer:

Originally Posted by eedoga

I shortened the quote but I hope I didn't change the meaning at all.

Hey Paul, I hope it works too, The kids did a bunch of math and then ordered a specific rubber from McMaster Carr. A few sheets of it are here and to be honest it doesn't seam very sticky to me, but if I put any weight on the sheet it is relatively hard to slide across my counters. I'm hoping it is sticky enough, if not I hope we can find a way to find softer/stickier rubber in time.

We may have to go with a stinger or wheelie bar idea, and in I have an idea as to how we could maybe do it, I'll have to look at the cad drawings.

As for the room in the top of the robot, there is a bucket that goes there for dumping disks in the top of the tower.

Thanks for the advice, I'll share it with the kids!

Edoga

[Justin m]

Actual post below, sorry

[Jeffy]

Originally Posted by Justin m

Actually, our team discovered that when driving at the corner, the angle of the bars relative to the robot is slightly larger than 90 degrees

Is this a joke?

If not,
The angle compared to the direction of gravity is the defining factor for friction via normal force.

If so, you got me.

[Nuttyman54]

Originally Posted by Jeffy

Is this a joke?

If not,
The angle compared to the direction of gravity is the defining factor for friction via normal force.

If so, you got me.

I believe he's not talking about friction, but about the vertex that sticks out at each rung level. He is correct that those vertices (which is 90 degrees projected in the ground plane) is larger than 90 degrees in the the plane normal to the corner poles.

That being said, I don't think this design relies on the corners being 90 degrees, they simply chose 90 as their angle between the climbing wheels. They should roll over the vertices regardless.

[eedoga]

So...we decided to go with magnets. We found 110 lb electromagnets on the interwebs, and the current plan is to use three of them to hold the robot down onto the pole. This should create enough "normal force" to allow the wheels to drive up the pole. the current design uses three electromagnets. two at either end, and one in the middle on Nylon straps that are just short of the pole. The magnets would then pull the robot down compressing the springs slightly. As the robot drives and reaches the cross beams the electromagent would be turned off allowing it to pass over the cross beam. with the other two magnets holding the robot down. the magnet would then be reactivated on the other side.

My current concerns...
- The battery getting hot from running the electromagnets.
- Adding three spike relays to our current cramped electronics board
- Having the magnets stick to things other than the pole
- Electrical issues stemming from having such powerful magnets in close proximity to everything else...
- the rules on electromagnets which I haven't looked up yet myself, but the team seams to think are A-OK...

Edoga

[Justin m]

Originally Posted by eedoga

I think part of the issue is that you are not seeing the whole picture.


The robot has two of the system you are looking at at a 90 degree angle to eachother with the wheels coming together in a V-shape. The bottom of the v is where the pole is of the corner of the pyramid hopefully will be. It is our hope that as the robot drives up the pole the wheels will sort of grip the pole. with the original design the triwheels were meant to rotate around the cross beams. We realized shortly after we selected this design that the triwheels would bind up as soon as they came to an obstacle and tried to rotate because the arm length is longer when the wheels rotate down then when the wheels are flat. So...we came up with the idea of having the wheels on articulating arms so that they can move up and out allowing them to rotate around. In this way we hope to drive over the cross beams and have the wheels rotate around them.

It is our hope that articulating the wheels will also allow the wheels to drive over the cross beams without tilting the robot over backwards.

Fingers crossed. :-)

Hope this helps clear things up a bit.

Edoga

Actually, our team found that when looking at the angle the robot interacts with the pole, the angle is slightly larger than 90 degrees at the intersections.