#robotics Logs

Feb 24 2015

05:53 AirForce590 hey
05:54 AirForce590 anyone?
05:54 AirForce590 deshipu:
06:03 veverak deshipu: lookas awesome
09:26 rue_more bah, I cant see youtube videos unless their enbedded
09:33 shipu en-beds his
10:30 LiohAu_ can anybody explain what this means "It is a dual motor driver specifically optimized for use in radio controlled vehicles." in this page : http://www.robotshop.com/en/sabertooth-dual-12a-regenerative-motor-driver.html ?
10:31 LiohAu_ hm.
10:31 LiohAu_ wrong key, I hope nobody answered too fast :(
10:34 deshipu LiohAu_: so, which word is unclear?
10:35 LiohAu_ why a motor driver is more suited for RC
10:35 LiohAu_ than another
10:36 deshipu LiohAu_: it takes PPM signal, I think
10:36 deshipu or PWM
10:36 LiohAu_ while other motor drivers uses ?
10:37 deshipu they can use anything, from I²C, serial, to even USB
10:38 deshipu they are usually just boards with an H-bridge and a microcontroller on board
10:44 LiohAu_ deshipu: my link was only a motor driver, so there's no controller, right?
10:44 LiohAu_ no microcontroller I mean
10:45 deshipu LiohAu_: well, there is a microcontroller on the board to take the signal you take and turn into signal for the h-bridge, but it's pre-programmed for that purpose and you can't (shouldn't) really reprogram it
10:46 LiohAu_ hm, so what's the point of buying motor driver board only, instead of buying the motor controller directly if that adds a microcontroller ?
10:48 deshipu the fact that it has a microcontroller is an irrelevant implementation detail
10:48 deshipu you can't use it for your purposes
10:51 LiohAu_ yes I understood this (since you said that I shouldn't reprogram it). But I would like to understand the point of buying a motor driver board instead of buying a motor controller ?
10:52 LiohAu_ If you buy a motor controller board, there's only 1 microcontroller right? if you buy a motor driver board, there's one that you can't use (only talk to), and another one that you need to talk to the motor driver.
10:53 deshipu I'm not sure what's the difference between driver and controller here
10:53 deshipu I use the terms interchangeably
10:54 deshipu they put the uc there to be able to have several modes and better control over some things -- like the overheat/overcurrent protection, etc
13:02 paul2520 http://spectrum.ieee.org/tech-talk/robotics/artificial-intelligence/building-ai-to-play-by-any-rules
13:28 deshipu that is all nice and well, but we need the specialized insects, not the metal humans
13:41 paul2520 why not both?
13:43 paul2520 also that article doesn't talk about metal humans... AI would almost certainly be used to some degree in specialized insects
14:09 deshipu it talks about the difference
14:10 deshipu and why not?
14:10 deshipu because we are instictivelly mortally afraid of metal humans
14:13 deshipu as a species, I mean
15:05 paul2520 deshipu: well, they mention that they're paraphrasing a sci fi author
15:06 paul2520 and I would disagree, I don't think we're instinctively afraid of metal humans. I mean, unless we somehow percieve them as predators or just because they're unnatural. but computers are unnatural and I think many people have gotten used to them
15:13 veverak paul2520: we are afraid of thinks that resembles us and are not us
15:13 veverak laptop doesn't resembler humab
15:13 veverak *human
15:13 veverak but metal human body doe :)
15:13 veverak *does
15:22 deshipu the uncanny valley
15:27 veverak nah
15:28 veverak force me somebody int ofinishing that god damn piece of !!!!!
15:28 veverak deshipu: made my robot smaller
15:28 paul2520 okay, that's fair
15:28 paul2520 I've heard of the uncanny valley
15:28 paul2520 interesting ideas
15:29 deshipu veverak: the rover?
15:30 veverak yeah
15:30 deshipu veverak: why?
15:30 deshipu veverak: size is not such a big deal for wheeled robots
15:30 veverak deshipu: bigger thing was too cmoplicated
15:30 veverak so I switched form rc-motor + gearbox to '360 servo'
15:31 veverak made everything smaller and makes the first prototypes cheaper
15:31 deshipu nice
15:31 veverak when I remove all bugs from 'small one' I will than switch to real thing :)
15:32 deshipu good plan :)
15:33 veverak yeah
15:33 deshipu also, with smaller size you don't have to care for inertia so much
15:34 veverak yeah
15:34 veverak everything is simpler!
15:34 veverak :D
15:34 veverak and I am also doing a lot of changes to the library code
15:34 veverak :/
15:35 deshipu fail fast, fail often :)
15:35 veverak yeah
15:44 paul2520 veverak: you're making a rover? awesome!
15:45 veverak http://letsmakerobots.com/parametric-robot-rover
15:45 veverak this is the state
15:45 veverak some time ago
15:45 veverak :D
16:19 Loshki deshipu: "#robotics is my life"..."that may be, but it doesn't have to be mine too". That's hilarious, you're here far more than I am.
16:19 deshipu Loshki: I do everything better than you ;)
16:20 Loshki deshipu: not quite *everything* :-)
17:32 paul2520 veverak: sweet!
18:03 veverak http://i.imgur.com/2Z5sBgl.png
18:03 veverak actual state
18:04 deshipu how do you attach the axle to the chassis?
18:05 veverak deshipu: geared wheels: big bearing
18:05 veverak (or bearing-alternative)
18:05 veverak front: just screw
18:05 veverak fron wheels got bearings inside of them
18:05 veverak *front
18:05 deshipu I see
18:06 deshipu and no wheels in the middle?
18:06 deshipu I guess not needed at this size and weight
18:06 veverak yeah, not in this version :)
18:06 veverak deshipu: it's two gearboxes and two row of wheels - less complicated
18:06 veverak :)
18:07 deshipu I thought you are using servos?
18:07 veverak yeah
18:07 veverak so no gearbox
18:07 veverak the bigger one got gearbox
18:07 deshipu ah, ok
18:07 veverak now I only need to finish the chassis, eletronics will be on top
18:08 deshipu what's the brains?
18:08 veverak arduin for testing I suppose?
18:08 veverak :D
18:08 veverak deshipu: for the bigger one I plan to put arduino nano inside
18:08 veverak and add i2c or SPI connector somewhere on the chassis
18:08 veverak and make the chassis waterproof
18:09 veverak :)
18:09 veverak or maybe BT
18:09 deshipu did you think about the sensors?
18:09 veverak yeah
18:10 deshipu you might need some chassis changes for things like bumpers
18:10 veverak deshipu: 'small' chassis won't bother
18:10 veverak bigger one will got mountings for that
18:11 deshipu looking forward to seeing it irl on a photo
18:11 veverak https://cloud.veverak.org/public.php?service=files&t=5d75d5963e0af05110de5528beb6e3f5
18:11 veverak you get the idea...
18:11 veverak :D
18:11 JT-Shop I have a ramps 1.4 rated at 24vdc. Is there a chart or formula for stetting the pots on the A4988?
18:11 JT-Shop setting
18:11 Tom_itx Triffid_Hunter how do you go about setting the current limit on the ramps boards?
18:12 JT-Shop hi Tom_itx
18:12 Tom_itx hi
18:12 JT-Shop the steppers are rated at 1.8A 1.8ohm 3.2 mH induction
18:13 Tom_itx yeah but you're using a chopper drive too aren't you?
18:13 Tom_itx same idea as the geckos
18:13 JT-Shop me?
18:13 Tom_itx yeah you
18:14 JT-Shop let me look up the gecko sheet
18:14 Tom_itx it uses resistors across a terminal
18:14 Tom_itx it's not gonna be the same
18:14 JT-Shop they use resistors across a terminal
18:14 JT-Shop and the stuff I've seen says set the pot to pin at some mV
18:15 Tom_itx rue_more hasn't gotten off work yet or he could probably help
18:15 Tom_itx he just finished building one
18:17 JT-Shop I just found this http://reprap.org/wiki/Pololu_stepper_driver_board
18:19 Tom_itx read the upgrades section
18:21 JT-Shop the resistor has 30C marked on it on my A4988
18:21 Tom_itx it makes the voltage divider easier to manage if you put a 51k there instead
18:21 Tom_itx apparently
18:21 JT-Shop had to use my microscope to read it lol
18:21 Tom_itx or 68k
18:21 Tom_itx heh
18:22 Tom_itx so with the 51k replacement at full swing of the pot the current is still gonna be around 2A
18:22 Tom_itx so it won't blow anything up
18:23 Tom_itx it would make adjustment easier probably... less sensitive
18:23 JT-Shop that's a pretty small part to try and change
18:23 Tom_itx that's not small!
18:23 Tom_itx :)
18:23 JT-Shop I just can't see me doing it lol
18:24 Tom_itx come on over and i'll swap em for ya
18:25 JT-Shop I'd love to but your a bit far
18:25 JT-Shop time to start dinner, thanks for the help
18:25 Tom_itx it'll work as is but you don't want to move the pot too far or it will overcurrent the drives and shut down the driver
18:25 Tom_itx http://wiki.xtronics.com/index.php/Resistor_Codes
18:26 JT-Shop I'll check what v-ref is and if it is close I'll go with that
18:26 Tom_itx k
18:26 Tom_itx you could put a meter in series with one of the windings
18:26 Tom_itx and check the current
18:27 JT-Shop max for my meter is 1A I think
18:27 Tom_itx oh
18:27 Tom_itx most have a 10A setting
18:28 JT-Shop your going to make me look huh
18:28 Tom_itx heh
18:28 Tom_itx the data sheet may have a table showing the vref / current relationship
18:28 Tom_itx allegro
18:29 JT-Shop yea add a 0 to that it's a Fluke 77 with 10A and 320mA
18:30 Tom_itx there's some math on that page showing the vref calcs i think
18:30 JT-Shop time for me to start dinner... yea
18:30 Tom_itx VREF max = (TrimpotMaxR/(TrimpotMaXR+R5)) x VDD = (100,000 / (100,000 + 20,000)) * 5 = 4.16V
18:30 JT-Shop Vref = 0.7A / 2 = 0.350V
18:31 Tom_itx just make sure whoever helps knows it's running 24v
18:31 JT-Shop ok
18:32 JT-Shop it's on 12v at the moment
18:32 JT-Shop just to be safe
19:04 AirForce590 yo, has anyone 3d printed a wheel or gearbox for parallax continuous rotation servos?
19:04 AirForce590 and if so, could I have the plans?
19:29 rue_more whats up?
20:33 Triffid_Hunter Tom_itx: actually I found the best way to smooth and cap the current limit was to stick a 1N4148 or similar signal diode across it
20:33 Triffid_Hunter Tom_itx: not only does it cap the current at about 1.5A (which is still above the driver's max given such a small PCB) but it also filters out a lot of supply noise, making the steppers quieter
20:33 Triffid_Hunter adding a ceramic capacitor between vref and ground also reduces noise noticeably
20:33 Triffid_Hunter that's for pololu's A4988 breakouts, other drivers may work differently
20:42 Tom_itx Triffid_Hunter where do you put the diode?
20:43 Triffid_Hunter across the adjust pot, so full scale is ~0.65v
20:43 Tom_itx hmm
20:43 Tom_itx i was trying to help JT-Shop get his set up
20:43 Tom_itx he's planning to build one and i suggested he get with you for some advice
20:44 Tom_itx did you change that resistor they suggested in that link above or leave it alone?
20:45 Tom_itx this http://reprap.org/wiki/Pololu_stepper_driver_board
20:45 Tom_itx that
20:46 Triffid_Hunter no I left it alone, adding diodes is a superior mod with a similar end goal
20:47 Triffid_Hunter gotta leave some current to keep the diode forward biased at a reasonable voltage, I don't want the thing to sit at 0.4v because the Vf is like 2uA
20:47 Triffid_Hunter current I mean, not Vf :/
20:50 Tom_itx he's a fairly early riser so maybe he can catch you in the mornings