Arm Placement on Bot?

[Po-ser]

I'm sure this topic has been discussed somewhere before, but I can't find it (big thanks if someone can redirect me!). My team has been discussing the placement of the arm on our robot for this year's game. Because of a certain impossible-to-describe design (my best attempt: "the arm swings over in front of the chassis sideways sort of" ), we think our chassis would be more stable COG-wise if we placed the arm all the way over to the right corner. I looked back and found this photo of wildstang from 2005:

http://www.chiefdelphi.com/media/img...4e5d9752_l.jpg

And was told that they had a hard time driving, since they had to aim for tetras with the corner of their robot. Could someone who's driven that bot or a similar one tell me if it's true? Also, are there any other notable pros/cons for putting an arm off to the side as opposed to in the center?

Edit** Actually, the more I look at it, the more I think I've got my facts wrong. That arm definitely looks like it's in the center. Question rephrased: Are there bots that have had their arms placed off the side in the past. If so, how do they drive?

Sorry again if this has already been discussed somewhere!

[Simon Strauss]

IF you are considering either loading or placing tubes onto the goal from the side of your robot like i think you are, the main issue i see is the increase in difficulty when lining up with your target. Unless you are running an omni directional drive base (which i probably would know about if you were) you need to think of the differences in parking a car head on vs. parallel with the street. Even if you arnt loading from the side and are simply mounting your arm offset to increase space for a ramp i still see the issue of that because your arm is not in the center of your drive base you will be forced to take multiple attempts at lining up with either a spider leg or a tube.

[MrForbes]

Originally Posted by Po-ser

Because of a certain impossible-to-describe design (my best attempt: "the arm swings over in front of the chassis sideways sort of" )

My reply has more to do with the design process you are using, than with arm location....but I've been telling the team members that if they have an idea for how to do something on the robot, they NEED to make a sketch/drawing of it, so we can all see if it is a feasible idea. If you can only describe it, but cannot draw it on paper, then don't expect to be able to build it. I've been getting good results, we have some almost feasible designs on paper!

Give it a try, draw the robot with your proposed arm, showing it in 3 views (top, side, front), and perhaps an isometric sketch if there are still questions. Also show the arm in several positions in each view, such as in the "stowed" position, and reaching a ring that's laying on the floor, and reaching a ring that you're hanging on each of the 3 levels on the rack, and in maximum extended position in each direction to see if it fits in the virutal 72" x 72" box.

Don't get too involved with making a perfect drawing with all the details worked out, that is for a bit later when you have a workable concept down.

Also consider using graph paper to get a feel for making sketches to scale.

[Po-ser]

Oh, we've got the idea down pat! I was just afraid to disclose the details and had no way to elegantly phrase the concept. Here's a crude drawing of the idea:

http://rassi.ath.cx/stuypulse/view_p...=Week-1&id=G11

[Jeff Rodriguez]

Are you talking about an arm like this?
http://invisiblerobot.com/robotics/r...4/p1050258.jpg

That is team 116's 2005 frobot. I would suggest talking to someone from tha team.

[Elgin Clock]

Originally Posted by Po-ser

Oh, we've got the idea down pat! I was just afraid to disclose the details and had no way to elegantly phrase the concept. Here's a crude drawing of the idea:

http://rassi.ath.cx/stuypulse/view_p...=Week-1&id=G11

Do you plan on taking your arm past the point shown in your 3rd view?
Also, I hope you are using the wide configuration when you do this - meaning the dimension of the chassis from wheel to wheel shown in this picture should be your widest allowable limit.
Tipping is always possible and will happen even when manipulating something as lightweight as a tube.

Also, to get maximum arm height you can start your purple arm piece more in the configuration of the second view but still inside the invisible limit box of the starting position. Just a thought.

[Po-ser]

Originally Posted by Elgin Clock

Do you plan on taking your arm past the point shown in your 3rd view?
Also, I hope you are using the wide configuration when you do this - meaning the dimension of the chassis from wheel to wheel shown in this picture should be your widest allowable limit.
Tipping is always possible and will happen even when manipulating something as lightweight as a tube.

Also, to get maximum arm height you can start your purple arm piece more in the configuration of the second view but still inside the invisible limit box of the starting position. Just a thought.

The idea was not to take it past the point shown in the third view.

To have the best ramp configuration, we're looking more towards a long 'bot. That's why I'm a little skeptical of the large, swinging arm, even if it would be lightweight. But I suppose that we'd have even more trouble if the arm were placed square in the middle as opposed to off to the side.

And that's true, about maximizing height. I should have thought of that.

Thanks for the advice!

[Elgin Clock]

Originally Posted by Po-ser

The idea was not to take it past the point shown in the third view.

Very good thought. Even the lightest arm would be very unstable at those heights and the weight of the arm itself when going past that point would make tipping an almost certainty.

Originally Posted by Po-ser

To have the best ramp configuration, we're looking more towards a long 'bot. That's why I'm a little skeptical of the large, swinging arm, even if it would be lightweight.

Also a valid concern on your part, even having an arm go up to the point on the 3rd view when the width is very short may pose a problem. The frame is not as wide, and the wheels are your only means of contact on the floor as far as stability goes.

Horray for design challenges.

Good luck in coming up with something effective.
It looks like a good plan so far.