#robotics Logs

Sep 05 2020

04:37 AM rue_mohr: how about one like (larger of course) ...
04:43 AM rue_mohr: http://ruemohr.org/~ircjunk/robots/arm10/p1110088.jpg
04:43 AM rue_mohr: its parallel....
04:43 AM rue_mohr: not too many other redeeming qualities really...
12:31 PM i-make-robots: rue_mohr well there are a few challenges: grip with the right force and don't burnout the motor. it's not hard to grip with a servo, tho it's usually not enough to pick up more than a few grams. also servos working hard to maintain grip tend to overheat and burn out.
12:32 PM rue_mohr: yep, less you make your own servos, but are you running steppers on that arm?
12:32 PM i-make-robots: our latest is this, based on a 3-jaw chuck. https://www.instagram.com/p/CEscMkgjnBd/
12:33 PM rue_mohr: do you want to stay with stepper based?
12:33 PM i-make-robots: yeah, we're running steppers at every linkage.
12:33 PM i-make-robots: with cycloidal reducers.
12:33 PM rue_mohr: did you find a way to make them yourself, or you going commercial?
12:33 PM i-make-robots: ourselves
12:33 PM i-make-robots: several iterations
12:34 PM rue_mohr: good show
12:34 PM i-make-robots: they're only about 60% efficient.
12:34 PM rue_mohr: I remember you were having issues with the plantary
12:34 PM rue_mohr: hmm
12:34 PM i-make-robots: i don't believe I've ever attempted planetaries. they've always had too much slop, right from the start.
12:35 PM i-make-robots: although I saw a gearbox that claimed 6 arc seconds backlash. they had tapered planetary gears.
12:35 PM i-make-robots: the axial pre-load reduced the backlash a lot.
12:36 PM rue_mohr: oh which one did I do it on...
12:36 PM rue_mohr: I did one with belts...
12:37 PM rue_mohr: ... hmm
12:37 PM rue_mohr: its not here
12:37 PM rue_mohr: wow
12:38 PM rue_mohr: it was only like 25 years ago
12:38 PM rue_mohr: the fingers were actuated along a slider
12:39 PM rue_mohr: a belt went around them
12:39 PM rue_mohr: each finger was attached to the other side of the belt
12:39 PM rue_mohr: i-make-robots, does that draw a bit of a picture?
12:39 PM rue_mohr: same movement you have, but a bit more slim
12:40 PM rue_mohr: what was I going to do on the new one...
12:40 PM rue_mohr: http://ruemohr.org/~ircjunk/robots/arm6/p1070916.jpg
12:41 PM rue_mohr: :) didn't actuate them yet
12:44 PM Tom_L: what happened to that big wire frame hexapod you were making?
12:44 PM rue_mohr: its still taking up 1/4 of the work table
12:45 PM rue_mohr: I havn't been able to correct the overload boards yet
12:45 PM rue_mohr: they trip too fast, they need a filter
12:45 PM rue_mohr: that was the issue, they tripped after 1 pwm pulse
12:46 PM rue_mohr: I did, after all, make them fast
12:46 PM Tom_L: way overloaded
12:46 PM rue_mohr: no
12:46 PM rue_mohr: the pwm pulses are individually over the 1A/motor limit
12:46 PM rue_mohr: but the average is much lower
12:46 PM rue_mohr: muuuuch lower
12:46 PM rue_mohr: but my cutouts are fast...
12:47 PM rue_mohr: enough to trip on just 1 pwm pulse over an amp
12:48 PM Tom_L: huh
12:49 PM rue_mohr: thats kinda what I said
12:49 PM rue_mohr: the current feedback is quite lot impedance, so filtering it right it a trick
12:49 PM rue_mohr: quite low
01:18 PM rue_mohr: jukebox is fighting
01:18 PM rue_mohr: apache wont allow the cgi scripts to run...
01:18 PM rue_mohr: they work tho, this is a bonus
01:31 PM i-make-robots: we tried these ideas: https://www.instagram.com/p/CEj8LmrDMjY/
01:32 PM i-make-robots: in v1, belt that moves to fingers. each finger grabs a different side of the rail.
01:33 PM i-make-robots: in v2, two screws. when the fingers touched the screws would keep turning and the whole hand bends in a curve.
01:33 PM i-make-robots: in v3, 2 jaw chuck.
01:34 PM i-make-robots: I have other ideas inspired by pro model grippers.
01:42 PM rue_mohr: the screw one would also be painfully slow
01:47 PM i-make-robots: bbl
01:47 PM i-make-robots: a single, larger thread down the center of two rails and only one moving finger might be a better way
01:48 PM i-make-robots: another is the nut pushes a triangle block that forces two fingers to move orthogonally.
01:48 PM i-make-robots: that's one of the more common schunk designs.