I’m trying to decide between the Lynx 6 and the SES arm for my mobile, autonomous robot project. The two deciding factors for me are the lifting capacity and the gripper abilities. I assume the greater lifting capacity of the SES is due to its more powerful servos? If so, can I simply order the Lynx 6 with the same servos as the SES–at least for the shoulder rotation?
I like the gripper on the Lynx 6 because of its wider opening–2" versus the 1.25" on the SES’s little gripper. I’d prefer even wider so that it could pick up a soda can which is wider than 2"–is this possible? For example, how wide is the grip opening on the Lynxmotion Robot Hand–the dimensions don’t seem to be posted alongside the part (productID=438–the forum software won’t let me post the link…)
Any other thoughts or experience comparing these two arms would be appreciated!
I can’t give you a side-by-side comparison, as I don’t have an SES arm, but…
The maximum grip opening on my Lynx-6 arm is 2.25 inches. The depth of the finger-pad portion of the grip is 1 inch though, so grabbing something like a soda can would require a bit of modification at best.
Another VERY important factor to consider is that the Lynx “C” gripper (as used on the Lynx-6 arm) and the “A” gripper (as used in the Lynx-5) both use MICRO servos for the gripper mechanism. These servos have limited available torque due to their micro-sized design, so even if you were to provide a modified claw design that was large enough to wrap around a can, your lifting ability would be a bit limited, probably to being able to pick up empty cans. I haven’t actually done any testing to verify this, or to determine the maximum grip force that the micro servos can supply before they start to skip teeth, so I can’t give you anything more than guesswork on that point.
Thanks for the replies. That’s a really good point about the limited gripper strength due to the micro servo. And I should have specified I am only interested in lifting empty cans so weight wouldn’t be much of an issue there. The heaviest object I have in mind right now is a tennis ball, which I would plan to “scoop” up by sliding the Lynx 6 style gripper underneath while partly open, then tilting backward before lifting. I weighed a tennis ball to be about 2 ounces.
The grip servo on my Lynx-6 extends about one inch below the plate that serves as the body of the gripper. When the gripper is positioned so that it is parallel to the ground, this servo projects about 1/2 inch below the lowest point of the wrist bracket mechanism, placing the centerline of the fingers at about 1.125" above the floor when the servo’s case is held flat against the ground. This may or may not be seen as an issue when it comes to picking up tennis balls.
You may look at installing the gripper rotated 180 degrees from the normal orientation, with the servo on top, and the gears on the bottom. In this orientation, the fingers of the gripper are less than 3/4 of an inch off of the ground when it’s held parallel with the surface. You can get closer than that if you go with a Lynx-5 type of orientation without the wrist rotation servo, since it’s that rotation bracket that bottoms out. I’d guesstimate that you might be able to get down to less than 1/2" from the ground with an inverted gripper and no rotation mount.
That’s a great tip about the scooping–thanks! BTW, is it possible to mount a standard servo, instead of the micro servo, on the gripper to actuate the opening and closing? The assembly guide points out there is a weight penalty but is it mechanically possible to do this anyway?
Nope. The cutout, mounting holes, and mechanism are sized specifically for a micro servo, and any modification for use with a standard-sized servo would pretty much require the whole mess to be re-engineered.
Many yonks ago, Lynx used to have a large gripper that was essentially a scaled-up version of the current “C” gripper. I only ever saw it attached to the front of a Lynx Hexapod 6 (Pre “extreme” model), but it looks to have been mechanically similar to the current gripper design.
<time passes, links are clicked>
Found it!
It was referred to as the “big grip”, and if I recall correctly, I think it was just about big enough to grab a soda can at its full-open position. you can see it mounted to the front of a 12 DOF Hexapod in a handful of projects here].
If you are picking up light weight objects like an empty aluminum drink can, you could probably very easily make wider jaws that attach to the normal jaws. These would extend beyond the normal jaw and would not be fully closed when the normal jaw is closed. The advantage of this setup is the extensions probably could be made simply with a couple of popcicle sticks and hot glue, and easily removable when desired (plus being very light weight).
Thanks Seamus for the clarification regarding the gripper servos for the “C” gripper. And great idea zoomcat for extending the gripper jaws.
I have one of the SES style grippers on hand (“Little Gripper”) and it takes a standard servo nicely. (Seems to be designed for it rather than a micro servo.) And it has plenty of surface area to attach some extensions to the jaws. These could even be offset toward the ground to make for easier scooping. The inner flat grip surfaces are also nicely suited to attaching force sensor strips. So I guess the SES arm would be the better choice for me unless there is a good reason to use a Lynx 6 arm but swap out the gripper.
