#robotics Logs

Sep 18 2015

03:59 wolfmanjm esp8266 + arduino mini pro (clone) ~= $8
04:00 wolfmanjm can't really beat that for pins and wifi ;)
04:25 Gyrth Hello. I'm doing some research on autonomous vehicles. And I'm really interested in SLAM and Odometry. But I'm a bit confused. The two terms seem to be very similar. Is SLAM mapping the location of the vehicle AND the environment. And Odometry is just the location of the vehicle. Am I right on this?
04:27 deshipu right
04:28 deshipu odometry is basically for knowing how far and fast you move from the origin
04:28 deshipu and which direction, etc.
04:29 deshipu slam is about knowing the environment and where you are in it
04:30 Gyrth Alright. Cool.
04:30 Gyrth So many libraries.
04:35 Gyrth What sensor information can be used? I see a lot of stereo camera setups. But I guess ultra sonar would works as well right? Or maybe a light based distance meter.
04:38 Gyrth And the amount of accelaration it had applied also could be included in the data. With the steering angle maybe.
04:40 deshipu usually you have a lidar and an IMU
04:40 deshipu also, encoders on the wheels
04:41 deshipu but you can do it with just encoders and bumpers
04:46 Jak_o_Shadows encoders are very important.
04:46 Jak_o_Shadows A lidar is nice, but not neccessary.
04:46 Jak_o_Shadows Basically encoders are your #1 thing, with other sensor type things being neccessary, but quality being more variable
04:48 deshipu it's hard to put encoders on the legs
04:48 deshipu even harder with propellers
04:49 Jak_o_Shadows True. Then you'd move to an IMU
04:50 deshipu also, encoders on wheels don't help you much in all-terrain setup, where the wheels don't always touch the floor
04:50 deshipu and even when they do, it's not very horizontal
04:50 deshipu but you are right, on flat floor encoders rule
04:50 Jak_o_Shadows They help a lot in robot competitions :D
04:51 deshipu never tried those
04:51 Jak_o_Shadows Neither have I, but it's a pretty common thing on the internet I think
04:51 deshipu from my observations thugh, they tend to favor a single design
04:53 deshipu which must be horribly boring
04:53 Jak_o_Shadows Yeah, but it's the challenge of doing something in a timeframe
04:54 deshipu timeframe?
04:54 Jak_o_Shadows well, you've got a deadline
04:55 deshipu you can always just start next year>
04:55 deshipu ?
04:55 Jak_o_Shadows eh, not always
05:01 deshipu I think I saw only one competition that I liked
05:02 deshipu it was an obstacle course for legged robots
05:02 deshipu there was lots of innovation there
05:02 deshipu each robot was completely different
05:03 deshipu also, there were usually many ways to avoid a given obstacle
07:58 elektrinis-wrk anyone can recommend a Delta type 3d printe to buy, not to build?
08:58 zylinx Hey all
08:59 zylinx I was wondering if anyone could give me some pointers. regarding servos
09:00 zylinx if a data sheet specifies a specific pulse cycle (eg 30ms in my case), do i have to give it 30 or is that like a max/min
09:01 zylinx because 30ms of period time = 33.33333.. Hz which im not sure how to program into my code
09:02 zylinx i see many servo's use 20ms period time, which is much rounder 50Hz
09:03 deshipu zylinx: what does the datasheet say exactly? link?
09:03 zylinx http://www.servodatabase.com/servo/futaba/s3003
09:04 deshipu that's no datasheet
09:04 zylinx ah
09:04 zylinx well in the specifications
09:04 deshipu it's crowdsourced info
09:04 deshipu anyways, it will work with 50Hz
09:05 deshipu it will just be weaker
09:05 zylinx oh?!
09:05 zylinx could i go below 30ms ?
09:06 zylinx so it is not weaker
09:06 deshipu it may behave weird then
09:06 zylinx ok
09:06 deshipu but if it's 33Hz, I think the difference is negligible
09:08 zylinx cool, thnaks deshipu! also that link i posted for crowdsourced specs seems wrong, it says Pulse Width: 500-3000 µs ..... but when i tried 3000µs it didnt sound happy
09:09 zylinx only went up to 2500
09:09 deshipu well, it's precentage of the whole period
09:09 deshipu so it's 3000 for 30Hz, I guess
09:10 deshipu will be different for 50Hz
09:10 zylinx Oh of course! damn im stupid lol
09:10 zylinx thanks again
09:11 deshipu no, wait, that would be the other way, around, would it?
09:11 zylinx hmm
09:13 zylinx i had freq. 50Hz and i pulsed 500µs and it was fine, pulsed 3000µs not happy
09:13 zylinx i will try on something closer to 30Hz
09:14 deshipu the way those analog servos are usually build, there is a PWM generator inside that is controlled by the pot, and then a comparator that compares that signal with the signal it gets from you
09:14 zylinx so i do need to match the freq. ?
09:15 zylinx well it seems to work on 50hz
09:16 zylinx is it really a precentage of the whole period? im confused now
09:23 deshipu I'm a bit fuzzy on how the comparator actually works, but I have the impression that it's just a capacitor that is charger by one signal, and discharged by the other, so what counts is the total energy of your signal
09:23 deshipu that's just my wild guess, though
09:23 zylinx ok so its kind of comparing the duty cycle
10:58 applepi Any recommendations on where to get really grippy wheels for climbing steep inclines with rough terrain?
11:12 robopal how large
11:38 applepi probably 6ish inches. i'm an FTC coach, and my kids are wanting to do large wheels to get over the "hurdles" this year, but I'm much more of a software the hardware guy, unfortunately, so i'm a bit torn on where to get them
11:39 applepi robopal: http://cdn3.volusion.com/vyfsn.knvgw/v/vspfiles/photos/am-3222-2T.jpg?1442240393 <-- that's what they have to climb, the top portion is about a fifty degree incline.
11:52 deshipu use wegs
11:58 SpeedEvil What is that?
11:58 SpeedEvil you go over the near-vertical side?
12:00 deshipu wegs are wheels+legs
12:05 applepi wegs is a thought, but it needs to be able to get around the rest of the track as well without damaging it or anything
12:11 deshipu applepi: http://letsmakerobots.com/robot/project/transforming-wheel-robot-20-build-your-own
12:13 applepi Well how neat is that
12:21 elektrinis-hme so, how about delta style 3d printer, that I could buy..
12:23 deshipu elektrinis-hme: how about you ask that on some 3d-printing related channel?
12:23 deshipu or forum
12:24 elektrinis-hme ok, will do
12:28 applepi actually, I think wegs would be problematic, I think you'd have trouble getting off the bar you were on before as you went up. great for stairs but maybe not so great for monkeybar style climbing
12:29 SpeedEvil that depends on the geometry of the 'hook'
12:29 SpeedEvil and the spacing of the bars.
12:29 SpeedEvil If you know the spacing and type of the bars, you can optimies
12:29 SpeedEvil Assuming you're not allowed to jump
12:34 applepi I don't know about allowed but it would be very difficult lol
12:36 applepi The spacing at the high part with no ground under you is roughly 5.5 inches between bars
17:30 rue_mohr deshipu, what wolf said,
17:31 rue_mohr atmel keeps their microcontrollers as microcontrollers
22:21 ace4016 hrm, anyone know where/how to get 1/8" pipe (possibly NPT pre-tapped/died) that is actually .405" OD pipe?
22:21 ace4016 silly dimensions not actually being the dimensions
23:12 adam789654123 ace4016: i know speedymetals has a bunch of sizes and materials that pipes can be made from
23:12 adam789654123 but the pipes cant be used for telescoping
23:13 adam789654123 last i checked anyway
23:42 ace4016 hrm, i'll take a look