Lynx 6 questions (Absolute novice)

Lynxmotion Robot Arms
1

I’m new to the forum and to robotics so please go gently with me. Also, apologies in advance if I am asking questions which have been answered elsewhere or which should be posted on a different section of the forum.

I can only ask my questions in laymans terminology as I don’t yet fully grasp the concept of dof or know the techie way to ask what I want to know but, in essence, I am looking to do the following.

I need a robotic arm where the first joint both swivels and pivots on 1 axis - I am happy that the Lynx 6 seems to be able to do this.

I need the second joint, presumable this is called the elbow, to pivot on 1 axis - I am also happy that the Lynx 6 seems to be able to do this.

The third joint, however, is where my uncertainty lies. In my project, I need it to both swivel and pivot on 2 axes. (I.e., Up, down, left, right, rotate left, rotate right.) My initial guess from looking at the videos of the Lynx 6 that I have found is that the third joint is able to swivel and pivot on 1 axis as well as pick things up with the grabber but that it doesn’t have the full range of movement I require. (I.e., It can move up, down, swivel left and swivel right but it can’t move left and right.)

Any answers will be gratefully received and, if I am not able to do what I want with the Lynx 6, any modifications I can make to the standard model or alternative product suggestions which do what I am looking for would be very appreciated.

My second question is more one of principle than concerning a specific product. Supposing a robotic assumes a particular position and the power to the arm is cut. Is there a mechanism/technique which can be employed using, say, hydraulic dampers or something else to cause the arm to maintain its position rather than simply slumping under the weight it is carrying? My project involves making the arm assume a particular position which it maintains for several hours before returning to the docked position and I need to be sure that if the power to it is cut it will maintain that position, even if it is carrying a little weight.

Thanks in advance for any replies.

2

Worm gears are one way to make an arm hold position without power. You’d have to custom design your own arm though. The original mechanical Radio Shack Armatron used worm gears.

Another idea would be to have some kind of locking mechanism for each axis/joint. The locking mechanism would have to be custom made.

For low-power support applications it’s hard to beat a fixed stand. Can you redefine the task such that you set down the item being manipulated when the arm powers down?

If there are a limited number of places where the item being manipulated can be gripped it’s still likely to be easier (and less expensive) to design a fixed stand than to custom design an arm with locking mechanisms or worm gears.

You might be able to build your third joint using the low profile axis to provide the swivel, and then regular brackets to make the second and third degrees of freedom.

Can you tell us more about your application?

Have Fun!

3

If I’m thinking of the right sort of dampeners, I’m not sure that they’ll hold it.

The pneumatic ones that I’m familiar with (the ones on your front door) only slow the shutting.

Perhaps, instead of a worm gear, you could use ratcheting gears.
(I’m not sure if that’s the proper term for it.)

You know, the thingers that go “CLACK-CLACK-CLACK-CLACK” when you use a drill on a low torque setting?

4

First off, thanks for the reply. Worm gears, having looked them up on google, seem like something that might be a solution for me. Is it feasible to use worm gears in a swivel mechanism as well at the left/right, up/down axes such that the arm would be unable to move in any direction once a position has been assumed? I can see in my mind’s eye how it would work on the first 2 axes but not for the swivel. The application for my arm would require it to be mounted on a vertical as opposed to a horizontal surface so I would need to be able to swivel, say, 20 degrees from the vertical and have it maintain that position if the power was cut.

This was more along the lines of how I imagined it could work but it sounds a little more cumbersome and, presumably, while the arm is in motion the lock wouldn’t be engaged so if the power failed during a motion the arm could still fall. Am I correct in my assumption?

This isn’t really a feasible solution for my project. The arm needs to do all the work independent of any stands or such like.

This isn’t really an issue for me. The connection between the arm and the item being manipulated is already defined and is very simple to implement.

That looks like a sensible solution to me. Am I correct in assuming that it isn’t really possible to add a third degree of freedom to the standard joint on the Lynk 6? (Of course, this presumes that my understaing of that joint having only 2 dof by default is correct.(up/down, swivel left/swivel right))

Is there a particular ‘regular bracket’ that you could recommend if I was to try to go down the route of using the lpa and 2 regular brackets to provide my 3 dof’s?

I’d love to but at the moment I have to keep the specifics fairly close to my chest as this is a prototype for a potential commercial venture I have had an idea for. I would hasten to add that I am not a company trying to freeload and sponge info off of an enthusiast’s site, just a regular bloke with an idea that could potentially evolve into a business and I want to build a prototype to discover if my idea is actually feasible.

I will, and thanks once again for your help.

Likewise, Nick, thanks for your reply. What you have said here has confirmed my initial thoughts. I need something to hold the arm, not simply slow it, but being a complete novice I had no idea how what I wanted to do was achievable.

I am keen to discover as many different alternative ways of achieving my objective as possible and that potentially sounds like another alternative. Do you know if it is possible to implement these kinds of gears such that they don’t make a loud audible noise? My potential application is in an environment when noise needs to be kept to a minimum.

5

Please excuse my ignorance. I have been giving some further thought to the idea of using worm gears for my project and the more I think about it the more it seems to make sense. I also can see now how worm gears would be a workable solution to the swivel as well as the pivot degrees of freedom on the joints of my arm.

Any further replies/ideas would be gratefully received.

6

I’ve looked at doing this a couple times, that is using worm gears for servo replacement, and it always seems like the right angle thing makes the servo huge. Also worm gears are not especially efficient at like 45 to 55% from what I have seen. Still if you can come up with a good configuration I for one would love to see (use) it. :slight_smile:

7

I’ve never seen a ratcheting gear that didn’t make that sound.

Also, I’ve given it a bit more thought, and it doesn’t seem like it would be a good choice.

Your servos would have to be strong enough to ‘clack’ the gear, but the force of gravity acting on the joint would have to be too weak to make the gear ‘clack’.

Unless you’re using a huge amount of reduction on your servos, then I highly doubt that this would be possible.