#robotics Logs

Apr 28 2013

02:13 MrCurious yup, its just like that.
06:38 Facepainter How do you compare torque force and ordinary force?
06:39 rue_shop2 you mean when they are mixed?
06:39 rue_shop2 !time
06:39 tobbor My watch says its 04:25AM Sun Apr 28 2013
06:41 Facepainter I'm not sure what you mean. I'm looking at some hydraulic cylinders and was trying to compare the force with hydraulic motors. One is defined in force, the other is defined in torque, so I'm trying to compare the force with either
06:43 rue_shop2 oh,
06:43 rue_shop2 apples and oranges, the motor is rotating the and cylinder is sliding
06:44 Triffid_Hunter Facepainter: torque is rotational force. if you have 1 kilogram.centimeter, then if your shaft has 1cm radius you'll get 1kg force at the edge. if it's radius is 10cm you'll get 100gm force
06:44 Facepainter ah good point thanks
06:44 Triffid_Hunter Facepainter: so it depends entirely on gearing, and the circumference of whatever it is you use to convert rotational to linear force
06:45 rue_shop2 or if you put the motor into a lienar actuator
06:45 Triffid_Hunter pretty sure that's covered by "whatever it is you use to convert rotational to linear force" ;)
06:46 rue_shop2 sorry flasheread
06:48 rue_shop2 1.5" foam
07:06 Facepainter i understand that linear force is different from rotational force but is it possible to compare them? to understand which is better for example, 10kgcm torque vs a 100 gm force?
07:06 Facepainter like is there a ratio or something
07:10 thegadfly Both torque and linear force have units of force times distance
07:14 Triffid_Hunter Facepainter: the ratio is set by the radius of your output lever and any gears
07:14 Triffid_Hunter Facepainter: if your output lever is 10cm long, then 10kg.cm will give 1kg force at the tip of the lever
07:16 Facepainter ohhhhh i understand
07:18 rue_house Facepainter, I thought you had a handle on all that?
07:19 Facepainter hmm? no i only knew how to deal with torque and recently just started looking up hydraulic system which led me to hydraulic cylinders talking about force
07:20 Facepainter i wanted to know how to compare
07:20 rue_house ah
07:20 rue_house how fast do you want your arm to go from straight out to stright up?
07:20 rue_house did we work out soemthing like 5 seconds?
07:21 Facepainter pretty sure you said 6 haha
07:21 rue_house k
07:21 rue_house holding how much weight?
07:21 Triffid_Hunter Facepainter: interestingly, torque * rotational speed = power
07:22 rue_house you said something like 2kg?
07:22 rue_house Facepainter, I cant really help with your project, your in the wrong timezone
07:23 Facepainter no that was what i could lift with servomotors but with hydraulics id want to lift something about 10kg?
07:23 Facepainter yeah man
07:23 rue_house ok, and the arm is about 1m long?
07:23 Facepainter 50cm long?xD
07:24 rue_house ok, so .5m, 10kg, in 5 seconds
07:24 rue_house peak torque at the pivot is
07:24 Facepainter well something from 5-10kg is fine
07:25 Triffid_Hunter when you involve time you need to start including power and mgh and all that
07:25 rue_house 500kg-cm
07:25 rue_house 90 degrees in 5 seconds is 1 rotation in 20 seconds
07:25 rue_house which is 3rpm
07:26 rue_house 500kg-cm at 3rpm
07:28 rue_house 15 watts
07:28 rue_house huh, when I do it another way I get 30W
07:29 rue_house oh .5m arm
07:29 rue_house yea 15 or 16w
07:29 rue_house at 12V, thats 1.3A
07:29 Facepainter ok
07:30 rue_house wonder how big a 16W motor is
07:31 Triffid_Hunter remember to calculate for inefficiencies
07:31 rue_house ok, 16W/0.70 = 23W
07:32 rue_house and thats being really insulting to a dc motor
07:32 rue_house its smaller than a sinshield winder motor, I'm sure of that
07:32 rue_house windshield
07:32 Triffid_Hunter gearboxes are rarely better than about 60% from what I've read
07:32 rue_house ah god point
07:32 rue_house good
07:32 rue_house ok, just read what I mean from now on
07:39 Facepainter what about using hydraulic cylinder? what would you need to calculate for that stuff
07:39 rue_house just basic levers
07:40 rue_house if the cylinder is 5cm away from the pivot, and the arm is 50cm long, the force available at the end will be 1/10 the max of the cylinder
07:45 rue_house haha oh no, its getting light
07:45 rue_house thats bad
07:45 Facepainter how is it getting light?
07:48 rue_house radiation from a nuclear reactor
07:52 Tom_itx the sun?
07:52 rue_house you can call it that if youwant, its still getting brighter
07:52 Facepainter oh i thought you meant the weight
07:52 Tom_itx must be time to get up then
07:53 rue_house tom, do you have a servomotor from an HP printer?
07:53 Tom_itx nope
07:53 Tom_itx well if i do it's in pieces
07:54 Tom_itx i took the encoders off
07:54 rue_house I need that name, its bhulherr or something
07:54 sw0rdfish tooties!
07:56 Tom_itx http://tom-itx.dyndns.org:81/~webpage/motors/motor3.jpg
07:56 Tom_itx those?
07:56 rue_house no thats a good one
07:56 rue_house I'm looking for a more mainstream cheap junk producer
07:57 Jak_o_Shadows I have some stepper motors, but they're rather flat. What would this generally mean with regards to speed/torque?
07:57 rue_house not much
08:00 Jak_o_Shadows cool
08:00 rue_house Facepainter, I cant find a motor for you to get an idea of price or size
08:00 rue_house goodnight
08:01 Facepainter good night and thanks
08:55 Modeuse sers
11:25 MrCurious well, i think i just discovered the cause of heat death on this laptop
11:25 MrCurious cat is sleeping on it!
12:10 rue_bed felt-a-choke-itis?
16:22 MrCurious everyone is too quiet! someone natter on about making a robot or something
16:44 xorly I am a robot!
17:16 MrCurious solder solder solder, drill, drill, drill
17:19 MrCurious only 3' of solder left... going to have to be careful
17:49 MrCurious ugh. superglue ALL over my hands and arms
17:50 MrCurious the worse part is glueing your fingernails to your skin
17:53 xorly MrSkilful :D
20:50 rue_house Lolina8088, ok!
23:19 MrCurious the power systems and the compute systems have been combined on a aluminum backbone. it all fits cleanly inside the 2x4 extrusion. just need a smaler crossover cable and i will be ready to seal it up
23:20 GargantuaSauce what are you building
23:20 GargantuaSauce that lipo array sounds like a fire hazard
23:21 GargantuaSauce i hope all the cells arent in parallel
23:21 MrCurious its in a 3S array
23:21 GargantuaSauce so yes
23:22 MrCurious well
23:22 MrCurious (1,1,1) || (1,1,1) || (2,2,2)
23:22 GargantuaSauce i would recommend a power schottky in series with each individual battery
23:22 MrCurious using the charge/discharge/test controler from a laptop battery cell
23:22 MrCurious gonna assume that is in the discharge controler already
23:22 GargantuaSauce charging them all as a group is asking for trouble i think
23:23 GargantuaSauce oh a controller with each set of cells?
23:23 GargantuaSauce ok
23:23 MrCurious as it charges them using +1, 2,3,4--
23:23 MrCurious 1 controler for the whole array
23:24 GargantuaSauce i think that is dangerous
23:24 MrCurious how so
23:24 MrCurious many laptops use 6 cells in a 3s configuration of (2,2,2)
23:24 MrCurious i can see if one cell gets out of balance
23:25 GargantuaSauce well aside from charging, when (not if, when) a cell fails its polarity inverts
23:25 MrCurious rly?
23:25 GargantuaSauce yeeeup
23:25 MrCurious these are from macbook pro batteries
23:25 GargantuaSauce not something you want to have a dozen other cells connected to
23:25 MrCurious 180Ah of lipo insanity
23:26 GargantuaSauce and you're right about the balancing part...and i'm pretty sure it's more likely than you think
23:26 MrCurious well, the whole assembly will be inside 3mm thick aluminum
23:26 GargantuaSauce the resistance of each battery probably varies more than a little
23:26 GargantuaSauce i guess if you design it to deflagrate safely :)
23:27 MrCurious thats the hope.... with a blow hole near the batteries to prevent pressure buildup
23:28 MrCurious now that its all glued up... cant easily convert it to using 3 charge controlers
23:28 MrCurious but if i use 3 charge controlers
23:28 MrCurious then the first pack to fail will transition into charge mode, and drag the others down faster
23:28 MrCurious possibly causing charge to ping pong back and fourth
23:29 MrCurious that seems problematic as well
23:29 GargantuaSauce probably...i'm not too familiar with how laptop charge controllers work
23:29 MrCurious i was content to leave it as "Magic"
23:30 GargantuaSauce as long as that magic doesn't burn down your house
23:30 MrCurious i would think, in parallel, the strongest battery would be the one to supply the charge
23:30 GargantuaSauce i mean it's not like macbooks are known to combust under certain circumstances or anything
23:31 MrCurious maybe i should source a 4 pole tripple throw switch
23:32 MrCurious shorted the array a few times today. made a real loud crack
23:33 GargantuaSauce should probably stick a temperature sensor in there too
23:33 MrCurious guessing (2,2,2) in a 3S would be safe
23:33 MrCurious the charge controler has one
23:33 MrCurious and its mounted on a aluminum back plane, so the cpu temp sensor will also betray temp
23:33 GargantuaSauce you are overloading the charge controller
23:33 GargantuaSauce i would not trust it to function correctly
23:33 MrCurious and the 10DOF sensor in there also has a temp sensor
23:34 GargantuaSauce seriously i would not sleep in a building that housed this thing
23:35 GargantuaSauce that is a lot of energy in a small place
23:35 GargantuaSauce take every measure at your disposal
23:35 MrCurious it is a lot of energy
23:35 MrCurious which i am now feeling more and more nervous about
23:36 GargantuaSauce and lithium batteries are well known to fail in scary ways
23:36 MrCurious it will live in an aluminum encolosure
23:37 GargantuaSauce anyway now that i've unsettled you a suitable amount, whats the thing they're powering
23:38 MrCurious this.
23:38 MrCurious http://rogerunwin.imgur.com/all/
23:38 GargantuaSauce oh yeah that
23:40 MrCurious uploading a pic of the brain/battery board
23:41 MrCurious reload... and see pics of the cpu+ power board.
23:44 MrCurious GargantuaSauce are you speechless in terror?
23:44 MrCurious well, each segment of the 3s array has identical type and count of cells
23:47 MrCurious if one of the cells in the array begins to drop below the others voltage (in its segment) it should begin to suck charge off the other cells in || with it
23:50 GargantuaSauce and what happens when cells in series get out of balance
23:50 GargantuaSauce i dunno i am pretty skeptical that this won't burst into flames at some point in the future
23:51 GargantuaSauce but it's all in the name of science!
23:51 GargantuaSauce what gps module is that
23:51 MrCurious i think i will partition the cells into 2 arrays of only like cells tomorrow
23:57 MrCurious the $8 one from hack a day with a $5 active antenna
23:57 GargantuaSauce sirf chipset?
23:57 MrCurious ublox
23:58 MrCurious http://emerythacks.blogspot.com/2013/01/u-blox-pci-5s-cheap-gps-module-for-your.html
23:59 MrCurious that one
23:59 MrCurious this charger appears to be LOWERING the voltage
23:59 GargantuaSauce cool