#robotics Logs

Jul 06 2015

03:17 Jak_o_Shadows didn't end up needing to
03:17 Jak_o_Shadows success.
03:23 Jak_o_Shadows I get the feeling the bed isn't quite level. By the weird blobbing
03:23 Jak_o_Shadows course, that could be the temperature being dodgy
10:17 blib1 anyone here who has done gps based navigation?
12:32 SpeedEvil blib1: what do you mean
13:02 deshipu Snake Monster is still kicking: https://www.youtube.com/watch?v=UrjP3WB3VsY
13:50 blib1 I am trying to make waypoints on my 4-legged robot
13:50 blib1 are there any libraries that allow you to take a bot with 4 wheels and move it to a desired gps location?
13:54 SpeedEvil blib1: you mean you can't compute directions?
13:54 SpeedEvil Work out angle and distance, turn to angle, go distance
16:40 Orpheon blib1, you'll find sadly that gps doesn't have even nearly the resolution you need
16:40 Orpheon not precise enough
16:50 blib1 Orpheon: I agree
16:50 blib1 what do you use?
16:53 Orpheon blib1, right now, haven't done this
16:54 Orpheon the most straightforward but probably not easiest are colored markers that you then image-detect and triangulate your position out of
16:54 Orpheon hard mathematically, requires a lot of processing, but easy to relocate or extend once you got the base working
16:55 Orpheon another way would be to simply model your own movement and ignore the error
16:55 Orpheon works for small, local stuff
16:55 Orpheon there are models to combine the two above approaches, see Kalman filters etc
16:55 blib1 Orpheon: is there a layman introduction to kalman filters somewhere?
16:55 Orpheon egh
16:55 Orpheon idk
16:55 Orpheon what is "layman"?
16:55 Orpheon do you know matrix math?
16:57 blib1 yes
16:57 blib1 Orpheon: something simple
16:57 Orpheon do you want the walker to just follow a certain path?
16:57 Orpheon if so, I think easiest is to put tape on ground and then do line-following
16:57 Orpheon that's rather simple
16:58 Orpheon if you actually want a grid system...a not too complicated hack that could work would be placing appropriate colored markers, and just estimating your current position from movement data until you have at least two markers in sight, and when you have that triangulate and overwrite movement data
16:59 Orpheon hacky and might have some warping, but should mostly work
16:59 Orpheon (put markers on corners, for instance)
16:59 Orpheon Kalman gives you a way to balance between estimate from movement and estimate from vision mathematically "perfectly" assuming linear error
17:00 Orpheon you could also try placing strips of colored tape on floor
17:00 Orpheon not sure how well that would work
18:02 blib1 Hyratel1: how does one compute the total weight that a bot can carry?
18:02 Hyratel1 depends majorly on the bot
18:02 blib1 I've a 4" wheel right now, and am carrying around 10lb
18:02 blib1 maybe less
18:02 Hyratel1 you need to know your rolling friction as a function of total weight
18:02 blib1 Hyratel1: Rated Load: 4.5 kgf-cm (62.5 oz-in) x 4 motors
18:03 Hyratel1 solid plastic wheels/tires have a flat or nearly-flat coef
18:03 Hyratel1 pneumatic tires increase sharply with increasing payload
18:03 blib1 Hyratel1: https://www.servocity.com/html/5_4__off-road_robot_tires__595.html#.VZsD3_m6dvI - these tires
18:03 Hyratel1 so your rolling chassis might work fine with just its own weight, but add 50# and it might not be able to move
18:04 Hyratel1 put 50# on a trailer with hard wheels, and it can tow it without issue
18:04 blib1 how can I calculate how much weight it can carry ?
18:04 Hyratel1 that's too open a question
18:04 Hyratel1 I need more params
18:05 blib1 told you the motors. Wheels. distance between the wheels is 12"
18:05 Hyratel1 what shape is the footprint?
18:05 Hyratel1 square, long, wide?
18:06 Hyratel1 wider frames can turn better but have poor straight line stability
18:06 blib1 distance between left wheels = 12" . Distance between left and right wheel = 8"
18:06 Hyratel1 and I'm not much familiar with those tires
18:06 Hyratel1 ok so a slightly 'long' frame
18:06 Hyratel1 but I still don't know enough to just tell you
18:07 Hyratel1 does it sound like the motors are straining?
18:07 blib1 nope
18:07 blib1 Hyratel1: what else does one need to calculate weight carried by 4 wheeled bots?
18:07 Hyratel1 turning torque-friction
18:08 Hyratel1 front-rear weight distribution
18:08 Hyratel1 weight distribution influences the turning torque
18:08 Hyratel1 if it's dead-center, all four tires will "scrub" equally
18:09 blib1 turning torque-friction - I don't know. Weight distribution is equal.
18:09 Hyratel1 if it's rear-shifted, the front wheels will have less weight on them, giving them less traction, and your rear wheels will scrub less
18:09 blib1 at least you can assume so
18:10 Hyratel1 if the batteries are the biggest mass item, aside from the frame, you can use that to estimate your weight dist
18:11 Hyratel1 blib1, hope this helped
18:12 blib1 Hyratel1: indeed the batteries are the biggest mass item for now
18:12 Hyratel1 with your frame, it seems you'll have to determine the max payload experimentally
18:21 blib1 Hyratel1: so with hard wheels, one can carry a large payload?
18:21 blib1 what's your motor rated at? how do you carry 60lb?
18:31 Hyratel1 it doens't /carry/ 60lbs, it /is/ 60 lbs https://dl.dropboxusercontent.com/u/33593534/images/Robot/DSCN2011-1k2.jpg
18:31 Hyratel1 30 amps each
18:32 Hyratel1 12v
18:34 Hyratel1 blib1,
22:01 rue_shop3 zippo:/files/programming/c/resistor# ./a.out
22:01 rue_shop3 Vin
22:01 rue_shop3 R2
22:01 rue_shop3 Vout
22:01 rue_shop3 R1
22:01 rue_shop3 Voffset
22:01 rue_shop3 Top resistor: 10000
22:01 rue_shop3 Input low value: 0
22:02 rue_shop3 Output low value: 1.25
22:02 rue_shop3 Input high value: 30
22:02 rue_shop3 Output high value: 3.75
22:02 rue_shop3 Voffset is : 1.363636
22:02 rue_shop3 R1 is: 909.090942
22:02 rue_shop3 I wrote a program I did!
22:02 Jak_o_Shadows I levelled the 3d printer bed!
22:02 rue_shop3 :( I'm sorry to hear that
22:03 rue_shop3 you gonna try again?
22:03 Jak_o_Shadows haha. Nah, levelled, as in it is perpendicular to the hot-end now.
22:03 rue_shop3 aaah
22:03 rue_shop3 good stuff
22:04 Jak_o_Shadows I have slight z-banding issues though.
22:05 Jak_o_Shadows But I don't think I have quite enough bed adhesion to print a replacement cold end.
22:06 Jak_o_Shadows So i'm looking for something smaller to print
22:12 rue_shop3 I'll be damned
22:12 rue_shop3 to offset a voltage divider you use the same divider ratio
22:12 rue_shop3 this makes sense
22:51 Hyratel1 Jak_o_Shadows, hey did you see the EZ-level bed design hackaday posted a day or so ago?
22:52 Jak_o_Shadows I might've missed it
22:53 Hyratel1 http://hackaday.com/2015/06/29/semi-automatic-bed-leveling-your-3d-printer/
22:53 Hyratel1 spring elevate with set screws
22:53 Hyratel1 springs soft enough that you can poke the head right onto the bed, and set screws to keep it where it gets pressed to
22:54 RifRaf biuld it rigid and level, it stays rigid and level
22:54 Hyratel1 RifRaf, except that you have to remove and reinstall the platform every print
22:55 Hyratel1 micro-changes in alignment change the performance
22:55 RifRaf what kinda platform, sounds like a hassle having to do that
22:55 Hyratel1 for ABS printing, probably a glass plate with clamps to keep it on the sub-bed
22:56 RifRaf a peice of kapton on glass tape last me at least a few months printing daily
22:56 RifRaf and no clamps, i screw the plater rigid
22:56 RifRaf plate*
22:56 Hyratel1 that's great
22:56 RifRaf yep, will help you if you want to avoid auto leveling all the time
22:56 Jak_o_Shadows I am mostly having trouble with z height
22:57 RifRaf z thumb screws ftw
22:57 RifRaf perfect for minor adjustments
22:58 Hyratel1 RifRaf, so are you saying the spring loaded levelling is a bad idea?
23:03 RifRaf Hyratel1: yes
23:03 RifRaf but i just am against springs on biuld platforms
23:25 Jak_o_Shadows Now, what is the ideal nozzle height?
23:26 Jak_o_Shadows I have a 0.2mm nozzle, and a feeler gauges
23:44 wolfmanjm 0.2mm nozzles are very hard to use. 0.5 or 0.4 are much easier
23:44 Jak_o_Shadows I don't have a j-head with interchangeable nozzle
23:44 Jak_o_Shadows But still, barring bed adhesion, and the slight z-banding, it's not too bad
23:44 Jak_o_Shadows Through the nozzle cone angle probably isn't sharp enough
23:45 wolfmanjm with a 0.2 mm nozzle I'd try a 0.1mm layer ht and 0.2mm width
23:46 Jak_o_Shadows I should be getting some acetone next week. Maybe printing ABS onto bare glass isn't the best thing.
23:46 wolfmanjm but width could be more than that, and ht could be as much as 1.5mm it'll take some experimenting to find the best ht and width
23:48 wolfmanjm the smallest nozzle I have is 0.35mm and it took me a while to get decent prints with it.
23:51 Jak_o_Shadows In general, I'm pretty happy with the quality of the prints. Stiffening the extruder up helped a bit.
23:51 Jak_o_Shadows I'll take a pic when i'm done.