Brainstorming: A swivel "waist" for a robot arm.

[Dan Linder]

The robot arm discussed in the other email thread is currently pointed straight ahead (90 degrees) of the robot chassis.  This means that the driver has to be able to come straight onto the object to pick it up - in many practice runs a piece would get lodged in a corner and they had to do some extra manuvering to get lined up.

As an upgrade we'd like to add a turntable of sorts.

Our first (albeit niave) attempt was to put the arm directly on top of the large servo, but that had two big problems: The splined shaft of the servo isn't big enough to balance the arm without using a small "table"+lazy susan arrangement.  Once we set that up, the arm was too high to do much good (we have a 30x30x30 cube limit, and the robot chassis we can't modify is about 4" to the top surface - a CeenBot for those who are interested).

I've looked at making a turntable out of a metal gear (roughly 3" diameter) and have the servo drive a smaller gear to provide some degree of movement.

Before we plunk down some cash to gerry-rig a turntable (2.5" 80T gear/turntable, 20T servo gear, turntable base = ~$40), does someone else have another ideas?

DanL

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[Rob Townley]

Never really built a robot but if you still end up using cables ....   A nephew purchased a trick bicycle for $25 last month.  The handlebars rotate 360°, 720°, ∞ ° even with the cables.  Normally, the cables limit how far the front wheel will turn.  If your team is already looking for bicycle cables, might have em look at a bike with ∞ rotation handlebars.  These would not have gear teeth and not sure how easy to add-on teeth yourself. 

Could a universal joint from the front end of a upullit car be made to work?  Maybe the spinning shaft changes the length of the cables?  Probably much more expensive and complicated. 

$40 sounds like a steal, however. 

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[Stephen Beck]

A while back (probably 2 years ago) I left a full pan-and-tilt security camera at the space. I'm sure the camera has disappeared by now but if it is still there you should take a look at it. I thought the method by which it achieved rotation and tilt was pretty awesome. I have another one at my house if you would like to play with it.

On Apr 2, 2014 10:53 AM, "Dan Linder" <d...@linder.org> wrote:

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[Kevin Fusselman]

I believe that this camera is still in the parts closet, top shelf, righthand side, near the back.

[Dan Linder]

I've been a long-time-lurker so this might get me to come out of my shell and come down...assuming it's open. :)

If not, could I say "pretty please" and have someone take a couple of photos of it and send them to me?

The mention of the universal joint got me to thinking about an alternative I might experiment with.  If I took some small/light U-Joints (more the size of a socket set), hopefully much more "loose" it might be possible to move each joint by pulling on one side with a cord and pull the other side back with a spring.  It would mean two servos per joint, but it would give great flexibility.  Though we might have to go up to the high-torque (higher cost) servos...

Dan

[Eric J. Kaplan]

The Makery will be open by about 10a on Saturday, until at least 4p. And again on Wednesday at 5:30p. 

As they say on the game show: "Come on down!"

Sent from Eric's iPhone