How do the grippers used in the Lynx arms deal with objects whose diameters/widths don’t correlate precisely to a point on the servo, or aren’t precisely known in advance? Do they have some kind of springs/shock absorbers buffering the actual gripper from the servo driving them? I’ll admit I’m a total servo virgin, but intiutively it seems like if you naively signaled the servo to close the gripper by (for instance) rotating to the 30-degree point, but solid resistance were encountered around the 34-degree point while rotating, you’d be in serious danger of burning out the motor, stripping the gears, or something comparably bad. But if you didn’t grip firmly enough, whatever it was you wanted to pick up would just slip through the grippers and fall.
The impression I’ve gotten so far is that low-cost robotic arms don’t seem to handle dynamic situations very well – the kind of situations where the arm, flanked by lots of sensors, would be expected to recognize and grab a variety of objects defined only loosely in advance by general rules, rather than operating in a “sealed” environment where the exact position and size of everything is presumed to be known in advance. Put another way, the difference between playing “Temple of Hanoi” knowing in advance EXACTLY where each tower is relative to the arm, the exact dimensions of each piece, and the exact location of each piece… vs expecting the arm to use its sensors to “look around” its immediate vicinity until it finds something resembling a Temple of Hanoi set, then using something like a CMUCam2+ mounted on it to determine its current state and solve it from that point forward.
Is that accurate? Or do grippers HAVE a certain amount of “springiness” in their grip to allow them to gracefully handle situations like that?
You are pretty much correct. Inexpensive servo based arms usually do not have built in feedback sensors to provide any environmental or conditional information to the controlling mechanism.
By some miracle, are the AX12 servos the right size to serve as drop-in replacements for the servos in the Lynx arms? Or at least the gripper? I know they’d need a totally different controller, but first and foremost they’d have to physically fit for me to even think about using them…
(sry for the double post) also i think the rubber on the gripper allows for quite a limited amount of springy-ness but if you really want to be able to gauge that, you can always hook up a pressure sensor on the gripper to allow the servo to stop closing when a certain pressure is detected, and if you really wanted to get technical, you could always hook the gripper servo up with an Open Servo thing, so that the servo would send the postion of the servo back to the mircro
that’s a nice little motor package (the AX-12) but it’s too bad they were so focused on selling their own bracket system and didn’t make it mechanically compatible (or have an adapter bracket even) with other standard servos.
I wonder if it’s possible to make a LM compatible bracket (from aluminum) that works with their servo mounting design. Be nice to have their level of electronics support in a mecchanically compatible form to the rest of my stuff. Hmm…
Seems that Styro-foam blocks are not a good item to move around, without creating some “foam gloves” for the grippers. Since stripping the gripper gears on these blocks I have decided to use sponge blocks for all future devleopment movements. Any Prototype “GLOVES” ideas would be appreciated.
We developed several videos of the L6 moving wood blocks. We limited the closed position to a value that could grip the blocks effectively and never had a problem with slippage or gripper servo gear breakage. However we encourage gripper experimentation and modification by the builders. We never intended the gripper on the L5 or L6 to be a perfect solution for every situation, but the robot kits do offer a stable, reliable, repeatable platform that can be modified to be suitable for most hobby applications.
