#robotics Logs

Feb 13 2018

12:05 AM rue_: at their upper rated voltage, servos usually aren't stable
12:09 AM rue_: you might be better off to run a switching supply to bring it down a volt or two, which also decreases your input current
12:09 AM rue_: so, what guage wire are you using for the 20A lines? 18?
12:09 AM rue_: you do know it should be about #12?
12:09 AM rue_: I also know you didn't read my servo howto
12:09 AM rue_: +- the drive method, their not drawing a continious 3A
12:09 AM AchiestDragon: yea , was running 6 of 5/6v 3a bec egulators 1 per leg but there dipping out on load need one per servo idealy 18 of them is a bit ott
12:10 AM rue_: you use a 1-2ms pulse to control them?
12:10 AM AchiestDragon: yea
12:12 AM rue_: I wonder how long they take to melt at 100% load
12:14 AM AchiestDragon: there only cheep £3.00 ones , they have not melted its the onboard logic chip thats fryed on them resistor regulaton for a 3.3v to 5v device so it works in the 4.5v to 7.2v range
12:15 AM rue_: no, the motors will burn up or generate enough heat to melt the case
12:15 AM rue_: the heat usually melts the gears via the motors shaft first
12:15 AM AchiestDragon: not had that happen , the motor loads are good and there metal geared
12:16 AM rue_: so if 1 motor pulls 3A, how much do 2 motors pull?
12:17 AM rue_: cause, the pulses aren't simotanious
12:17 AM AchiestDragon: 6a if the same load
12:17 AM rue_: unless your trying to kill soemthing
12:18 AM rue_: no, the drive pulses start at different times
12:18 AM AchiestDragon: not all servos should be full oad all the time
12:18 AM rue_: do you know when the drive pulse starts to the motor?
12:20 AM AchiestDragon: no , but again some may as theres 3 separate adruinos driving 6 servos each
12:22 AM rue_: http://ruemohr.org/~ircjunk/tutorials/elex/hobbyservo/servo101.html
12:22 AM rue_: the motor drive pulse starts when the control pulse ends
12:23 AM rue_: http://ruemohr.org/~ircjunk/tutorials/elex/hobbyservo2/p1080888.jpg
12:23 AM rue_: servo drive current sensor
12:24 AM rue_: keybaord isn't really that bad, its the camera...
12:24 AM rue_: http://ruemohr.org/~ircjunk/tutorials/elex/hobbyservo2/p1080887.jpg
12:24 AM rue_: the top trace is the motor drive current detect, the bottom trance is the control pulse
12:24 AM rue_: so that servo is at about 60% load
12:25 AM rue_: did you know an stm32 can drive up to 88 servos?
12:25 AM rue_: before you need to start compromising resolution
12:27 AM AchiestDragon: maybe but i have pots on each joint for pid control so need an analog in for each pwm out
12:29 AM rue_: you didn't want to tap the servo thats on the 2.5V reference in the servo?
12:29 AM AchiestDragon: the pots (with metal d shafts) also work quite well removing the need for servos with 2 output shafts
12:30 AM rue_: indeed
12:30 AM rue_: the pot in the servo runs off a 2.5V reference supply in the chip
12:31 AM rue_: they use the cutest little smd mosfets in those for the bridge...
12:34 AM AchiestDragon: if i tapped into the servo pot then i would then need servos with 2 output shafts or a second shaft bearing an mount
12:34 AM rue_bed: why
12:36 AM rue_bed: or do you mean the pot is an integral bearing in the design of the joint
12:36 AM rue_bed: like my hexapod
12:36 AM AchiestDragon: https://drive.google.com/file/d/1JOmX1tFKtqB2a8Q7nXeF4LjW7pb6mfzs/view?usp=sharing
12:36 AM AchiestDragon: yea
12:36 AM rue_bed: wow konquerer just shows a white page
12:37 AM rue_bed: ah nice
12:37 AM rue_bed: you could make a dummy joint
12:37 AM rue_bed: er, pivot
12:37 AM rue_bed: I mean, if its already made then whatever
12:38 AM rue_bed: you print the controller too?
12:38 AM AchiestDragon: just as easy to use a pot that i can wire to easy without having to also drill holes in servos for extra wires
12:39 AM rue_bed: what sensros do you have on the feet?
12:39 AM rue_bed: and what did you design it in?
12:43 AM AchiestDragon: switches well the foot is 2 halves with a spring and some contacts so it works as a switch and with a +-60 degree actuation angle
12:43 AM rue_bed: http://ruemohr.org/%7Eircjunk/robots/frankenhex/p1090368.jpg
12:43 AM rue_bed: I still need to work out all the offsets and scalings for that one
12:43 AM rue_bed: cool
12:43 AM rue_bed: I have NO idea if it can walk
12:43 AM rue_bed: I half expect the servos will catch fire just trying to stand still
12:44 AM AchiestDragon: same :)
12:44 AM rue_bed: usb joystick?
12:44 AM AchiestDragon: yea
12:44 AM rue_bed: heh
12:45 AM rue_bed: what did you use for the joystick gimbal, is it printed?
12:46 AM AchiestDragon: adruino nano , the joysticks are https://www.ebay.co.uk/itm/262958540470
12:47 AM rue_bed: eeek $12
12:47 AM rue_bed: 4axis!?
12:47 AM * rue_bed segfaults
12:47 AM AchiestDragon: 3 and a button
12:51 AM AchiestDragon: https://github.com/achiestdragon/leggie/tree/master/USBjoystick1
12:52 AM AchiestDragon: got to add output to the other serial port so could use a serial to rf link module rather than wired over usb
12:59 AM AchiestDragon: i still have the fealing i may need to reprint the legs a bit shorter
01:13 AM Jak_o_Shadows: They are pretty nice sticks
01:14 AM rue_bed: I was keeping the segment I did pretty short
01:14 AM Jak_o_Shadows: The x, y axis are spring loaded? The z is not?
01:14 AM rue_bed: I think it'll have to keep them tucked in
01:14 AM AchiestDragon: the x,y and z are all spring loaded
01:15 AM Jak_o_Shadows: Remove the z twist on one of em?
01:15 AM Jak_o_Shadows: for throttle/
01:17 AM AchiestDragon: lol ,, one is x,y walk dir with z being turn , the other is x y body tilt and z hight ,, i may remove the spring on z hight
01:20 AM Jak_o_Shadows: oh yeah.
01:20 AM Jak_o_Shadows: that works too
07:18 AM squirrel1 is now known as veverak