#robotics Logs

Feb 10 2019

01:22 AM mrdata-: if they drift, they need to be calibrated
01:45 AM rue_shop1: no its pieze
01:45 AM rue_shop1: piezo, you cant get an absolute anything from them
01:45 AM rue_shop1: ok, I got the talking library working for arduino, thats halarious
03:55 AM mrdata-: for a pressure sensor, you have a membrane separating the test gas from a known amount of gas
03:55 AM mrdata-: you calibrate it by subjecting it to a known pressure
03:56 AM mrdata-: or a sequence of known pressures
03:58 AM mrdata-: if that membrane is a metal plate that is a variable distance from a base plate based on the pressure
03:58 AM mrdata-: then your capacitance gives you a reading
03:59 AM mrdata-: of course the plates will experience an attractive force when you charge the cap
04:00 AM mrdata-: which will move the plate i guess, but it isnt completely free to move because the known amount of gas builds up in pressure as well
04:01 AM mrdata-: so it should be possible to calibrate
04:02 AM mrdata-: rue_shop1, ^
04:14 AM rue_mohr: I can just do a sweep of pressure on it
04:14 AM rue_mohr: the signal on the plates is at 20Mhz, so mechanical stuff wont be an issue
04:15 AM rue_mohr: I'm interested to know how much signal I'll get
12:25 PM DrunkenDwarf: Hi all. I have a question about Hexapods. I do simple linear robotics at work, but never tried anything articulated. I've been watching clips of Orwel (https://www.youtube.com/watch?v=IAX3vwjZ4m4) and the freedom of movement is beautiful, I noticed it has 3 joints per leg rather than 2. Nearly every other hexapod I've seen has 2 joints. Is there an advantage to 3 joints? I'm wondering if theres much a 3
12:25 PM DrunkenDwarf: jointed leg could do that a 2 jointed one could not to justify the extra cost/power consumption/IK complexity.
01:03 PM mrdata-: DrunkenDwarf, how many joints per leg do crabs have? or other creatures
01:03 PM mrdata-: nature can guide us
01:04 PM mrdata-: it's a matter of degrees of freedom
01:07 PM Elleo: 1/13
01:07 PM Elleo: oops
01:08 PM polprog: ive got like 12
01:08 PM mrdata-: hip, knee, ankle, ...
01:08 PM polprog: toes
01:08 PM mrdata-: shoulder, elbow, wrist, ...
01:09 PM mrdata-: along one digit, how many joints back to the spine?
01:09 PM mrdata-: the human hand is complex though
01:10 PM mrdata-: should we count bones inside the hand and foot?
01:11 PM mrdata-: cnc machines need at least 3 axes
01:11 PM mrdata-: but six-axis machines exist
01:50 PM DrunkenDwarf: mrdata-, crabs have 3 per leg, as do spiders. But most robotic hexapods have 2, which says to me that that's enough for 6 legged movement. one of my requirements through is to position my hexapod over an object at a set distance with the first section of leg held completely horizontal. With a customary 2 jointed leg I'm not sure whether one movable pivot point is enough to stabilise on uneven terrain.
03:07 PM rue_mohr: life!
03:09 PM deshipu: spiders and crabs actually have 4-5 degrees of freedom per leg
03:10 PM deshipu: nature is wasteful
03:10 PM deshipu: you can't have a properly walking (without slipping) robot in a spider configuration with just 2 degrees per leg
03:10 PM deshipu: because you can't move the leg in a straight line then
03:12 PM DrunkenDwarf: I may have been misleading to be honest, when I say it has 2 joints, the shoulder joint had 2 axis of rotation, with a single axis of rotation on the "elbow" joint
03:14 PM DrunkenDwarf: as an example of what im talking about: 3 Joints (inc. bi-direction shoulder): https://www.youtube.com/watch?v=X5PeB-5fWGM ... whereas 2 joints (inc. bi-directional shoulder): https://www.youtube.com/watch?v=byzP9QiFadI
08:40 PM rue_shop1: :/ the pressure sensor works, but doesn't put out enough signal
08:57 PM Tom_L: op amp?
08:57 PM rue_mohr: no, its not over the noise, not worth it
08:57 PM rue_mohr: I could try it with a larger disc, but ~
08:57 PM rue_mohr: I got fittings for 1/2" 3/4" and 1"
08:58 PM rue_mohr: it DID take me like 4 hours to make the test
08:58 PM Tom_L: time well spent?
08:59 PM rue_mohr: meh, I learned things
08:59 PM Tom_L: how much pressure are we measuring?
08:59 PM rue_mohr: I needed to make round discs, so I did the sandwich-in-wood trick
08:59 PM Tom_L: oil pressure sensor from an automobile
09:00 PM rue_mohr: for 10c?
09:00 PM rue_mohr: I need 94 of them
09:01 PM Tom_L: you need 94 reliable of them
09:07 PM rue_mohr: http://ruemohr.org/~ircjunk/projects/presureSensor/slide.htm
09:07 PM rue_mohr: didn't have any dowel }:/
09:08 PM rue_mohr: one of the dics slipped and I couldn't get them down to the size I wanted
09:08 PM rue_mohr: I THINK the trick is actaully to put sandpaper between them.. no, that would be bad too.... hmmm
09:09 PM rue_mohr: ugh, dont feel like fixing the spelling...
09:09 PM Tom_L: double back tape
09:11 PM Tom_L: what's the hole for?
09:11 PM rue_mohr: air and wire
09:11 PM rue_mohr: the middle disk is sealed
09:11 PM rue_mohr: its the stator if you will
09:12 PM rue_mohr: the idea is that it'll bow ) ever so slightly with the pressure
09:12 PM Tom_L: wood will rust your lathe
09:12 PM Tom_L: clean it
09:12 PM rue_mohr: it would help if I gave it a concentric stamp
09:12 PM rue_mohr: yep, its all cleaned off
09:13 PM rue_mohr: wood is a fire hazard too, so I clean that up pretty quick
09:15 PM rue_mohr: ok, was still logged in, fixed spelling