#robotics Logs

Nov 29 2011

09:58 KongfuPanda Hello robotics people :)
09:58 KongfuPanda now that I'm done with my homework for this term I can spend some time working on my robot :)
10:09 Tobias| Nice :)
10:31 parag0n KongfuPanda, url?
10:32 KongfuPanda parag0n, to see my robot? it's not very profession , because I'm an enthusiast :) but you can read how I'm building it here: http://read-stuff-here.blogspot.com
10:33 KongfuPanda currently I'm replacing all screws and servo heads to make the legs less flexible
10:33 parag0n nice, i had a balsa hexapod myself
10:33 parag0n never got it walking though, it was too weak to hold a battery :(
10:34 parag0n its cute :)
10:35 parag0n http://www.youtube.com/watch?v=jUfCi0i86kk <-- my latest robot
10:35 KongfuPanda parag0n, what's a balsa hexapod?
10:36 parag0n a hexapod made of balsa wood
10:36 KongfuPanda your latest robot is cute too :D
10:37 KongfuPanda parag0n, oh I see. Mine can just barely lift 3 batteries, but it's struggling. I will need to get a LiPo battery later
10:37 parag0n http://thinkl33t.co.uk/uploads/r3/r3-gearbox.png <-- my next robot
10:37 KongfuPanda but the ones I got now are just soo cheap and easy to charge
10:37 parag0n i'm a big fan of lipo batteries
10:37 KongfuPanda oh nice, you are doing it properly :D
10:38 parag0n hve way too many of them now
10:38 KongfuPanda I didn't design my robot :D
10:38 KongfuPanda parag0n, how much is a cheap charger? everywhere I looked the chargers cost tonnes of money
10:38 parag0n yeah, after buying way too many wrong things for r2, i decided to design r3 before starting
10:38 parag0n mine was £15
10:39 parag0n http://www.hobbyking.com/hobbyking/store/__216__408__Battery_Chargers_Acc_-Battery_Chargers.html
10:39 parag0n i'd suggest http://www.hobbyking.com/hobbyking/store/__5548__IMAX_B6_Charger_Discharger_1_6_Cells_GENUINE_.html
10:40 KongfuPanda it's USA :(
10:40 parag0n also get a power supply from there, and a lipo charge bag (unlikely, but helps if you have a fire while charging)
10:40 parag0n hobbyking has warehouses in hongkong / germany / usa
10:41 KongfuPanda parag0n, I will need a 6-7.4 V battery, can that charger do it?
10:41 parag0n yep
10:41 parag0n you're looking for a 2S battery
10:41 parag0n 2S means 2 cells in series
10:41 parag0n lipo cells are 7.4v
10:42 parag0n well, they can get as high as 8.2 straight after charging
10:42 KongfuPanda I know
10:42 parag0n wait, that was wrong
10:42 parag0n a single lipo cell is 3.7v
10:43 parag0n they can get up to 4.2v after charign
10:43 KongfuPanda I have Li-ion now (just camera batteries NB-2L . 7.4V 1800mAh (non-genuine), genuine is only 700 mah.
10:43 KongfuPanda well, three in parallel ~ 5400 mah
10:43 KongfuPanda they go to 8.4V after charging
10:44 KongfuPanda and a few different capacitors in series
10:44 KongfuPanda to improve battery life
10:45 parag0n something like http://www.hobbyking.com/hobbyking/store/__14327__Turnigy_5000mAh_2S_30C_Lipo_Pack_DE_Warehouse_.html would probably work
10:51 KongfuPanda looks very nice
10:51 KongfuPanda why it only has 2 /5 rating?
10:53 KongfuPanda hmm
10:53 KongfuPanda that's weird, it says on the website that each of my Li-ion batteries weighs 31 g, then 3 of them weigh say ~100g. How come that lipo battery weighs 291 g?
10:54 KongfuPanda probably the website is not accurate
10:56 KongfuPanda I need to weigh them myself
10:58 KongfuPanda hmm, I don't have a sensitive enough balance
10:59 KongfuPanda well, most websites say ~up to 60 g
10:59 KongfuPanda but anyway, it's 180g for 3 of them , 5400 mAh. 7.4V.
11:00 KongfuPanda I don't understand, so getting that lipo battery will be even worse than my current setup?
11:03 parag0n i suspect that the rating on your batteries is a lie tbh
11:03 parag0n you cant really get 1800mAh li cells that small
11:04 parag0n lipo has a better power density than Li-ion, so if two cells have the same capacity, the lipo should be smaller
11:19 KongfuPanda I see
11:19 KongfuPanda how can I check the capacity on my Li-ion batteries?
11:19 KongfuPanda it's from ebay, so it's probably a lie
11:49 KongfuPanda parag0n, I'm going to discharge my battery over a small fan for ~10 mins and see if I can find the charge stored :D
12:08 KongfuPanda parag0n, I found an old 12V fan, so I connected it to the battery with A-meter in series :D taking current reading as time goes on
12:08 KongfuPanda hopefully this can give me a rough idea of mAh
12:08 KongfuPanda this fan has a lED , so cute :)
12:50 KongfuPanda parag0n, so far it gives ~ 1.6mAh very rough estimate
12:52 KongfuPanda but it's very inaccruate
14:23 Jeemy did any of you already try to power a usb webcam on a CAT5 wire?
14:23 Jeemy by connecting each USB pin to a single CAT5 wire
14:24 Jeemy and wiring the data wire through the CAT5 to
14:26 Jeemy on a classical webcam, the current rating are 500mA on 5V, while the the maximum allowable current on a CAT5 wire is said to be 577mA
15:23 dehuman a 14-channel digital wireless neural/EMG telemetry system, suitable for in-flight neural recording from flying insects such as dragonflies. It has a system mass of only 38 milligrams. The IC is powered by RF energy harvesting and consumes less than 1.23mW. It digitizes 10 neural and 4 EMG signals with 11 bit resolution as a 5 Mbps backscattered data stream at UHF (902-928 MHz). It has been fabricated in a 0.35um 4M1P CMOS process.
15:23 dehuman http://robots.net/article/3269.html
15:42 amee2k Jeemy: i'd say it should work over short runs. you may need some impedance matching though. USB is supposed to be 90 ohms between lines and 30 ohms to ground
15:42 amee2k not sure what cat5 cable has
15:44 Jeemy ok
15:44 amee2k with a little bit of luck i wouldn't expect many problems up to full speed, high speed could be a challenge though
15:45 Jeemy it seems that the 477mA current limit is for a 48V signal, so I would not have any problems regarding to power transport
15:45 amee2k not really
15:46 amee2k you could use two pairs for supplies instead of two wires, that would double the current capacity
15:47 Jeemy yes, but the idea would be to have 4 wires to get the webcam, and then be able to drive a little servo to rotate the webcam
15:47 amee2k one pair for data, two pairs for supply and ground leaves one pair unused, no?
15:48 Jeemy yes
15:48 Jeemy true ^^
15:49 amee2k if you use RC servos, they only need a PWM signal which fits on one wire
15:49 Jeemy yes that leaves me one wire
15:49 amee2k otherwise put a small microcontroller on the end
15:49 amee2k one?
15:50 amee2k oh, you only need one axis of rotation?
15:50 Jeemy yes :)
15:51 amee2k if this is for remote surveillance you could use the last wire for an IR LED spotlight?
15:51 amee2k or to tilt up and down too
15:51 Jeemy It is for a UAV waterproof webcam
15:54 Jeemy so a 360 view is enough to begin with
19:59 rue_house rs485 is nice for that, or 422
19:59 rue_house if you can do a twisted pair or two
21:12 zhanx ok time to back up the windows box and all the great fun that goes with it.
21:12 Tom_itx spare drive
21:12 zhanx yea, i am cleaning up old files first
21:12 Tom_itx you do that after a crash
21:12 zhanx and making tar's of my 14 gigs of photos
21:13 Tom_itx do you know where to get the Cortex M4F technical reference manual?
21:13 Tom_itx i have the RM0090 Ref Manual
21:13 zhanx nope, i am just looking at their code. i didn't know there was anything beyond the datasheet
21:14 Tom_itx nevermind
21:14 Tom_itx i found it i think
21:14 Tom_itx which data sheet?
21:14 zhanx quick google found it tho
21:21 duckinator hi
21:22 Tom_itx yeah, it looks to have the register info in it
21:28 thylyn okay #robotics, how much does a QBO robot cost?