#robotics Logs

May 21 2015

09:40 rue_house ya know when you make a really dodgy change to some code and you know the odds of it just owkring are low?
10:57 deshipu rue_house: that's why I avoid languages that have syntax which I can't emulate in my head
10:58 deshipu or at least parse
15:33 AWSrobot Help!
15:37 shipu sends helpful ro
15:38 AWSrobot I'm using an L298n motor driver to drive my motors; when I try to power it with a 9V the motors just whine and don't rotate. The voltage output is 5V from the motor controller if I use the 9v battery and use the multimeter to measure leads directly, but if I put it across the contacts of the motor it drops to 0.05V. However, if I replace the 9V battery with a 12V lab power supply that plugs into the wall, it not only runs, it runs with no
15:38 AWSrobot voltage loss.
15:38 AWSrobot Why?
15:39 deshipu alkaline batteries suck
15:39 AWSrobot ?
15:39 deshipu 9V ones especially
15:39 AWSrobot wut
15:39 deshipu they can't produce enough current for most uses
15:39 deshipu too low C rating, if you will
15:40 AWSrobot what do I do about this
15:40 deshipu use a different battery
15:41 deshipu one that can provide enough current for how the motors are rated
15:41 AWSrobot okay
15:41 AWSrobot how do I know what the motors are rated
15:41 deshipu you check their datasheet
15:41 AWSrobot I don't have a datasheet
15:41 AWSrobot they came with the tamiya package
15:42 deshipu you ask the seller for a datasheet, I guess
15:42 deshipu I think you can also measure the motor's resistance and calculate from that somehow, but I have no idea how
15:43 AWSrobot fa-130 motor
15:43 AWSrobot https://www.pololu.com/product/77
15:44 deshipu Stall current at 3 V: about 2.10 A
15:44 deshipu yowza
15:44 AWSrobot okay what does that mean exactly
15:44 deshipu Free-run current @ 3V:150 mA
15:45 deshipu that means that it will consume between 150 and 2100 mA of current at #V
15:45 deshipu at 3V
15:45 AWSrobot is that a buttload of current
15:45 deshipu the max you can get from an USB port is 500mA, for example
15:46 deshipu it's not that huge for a motor, they tend to be power hungry
15:46 AWSrobot it makes sense that it would be
15:47 AWSrobot Okay so I tried it, after you said that, with a 16.5V rechargeable RC car power pack
15:47 AWSrobot and it worked
15:47 AWSrobot but then it ran down
15:47 deshipu http://www.powerstream.com/9V-Alkaline-tests.htm
15:48 deshipu that motor is made for 3V
15:51 deshipu see what happens with it with higher voltages https://www.pololu.com/docs/0J11/all
15:56 AWSrobot ok
15:57 AWSrobot what kind of battery is more appropriate for powering robotics?
15:59 deshipu AWSrobot: I mostly use LiPo batteries, they have very nice weight to capacity ratio, and you can get them with high C rating
15:59 veverak :)
15:59 AWSrobot cool
15:59 deshipu AWSrobot: a battery from an old cellphone would work too
15:59 veverak deshipu: I am now considering 12V battery for rover robot
15:59 AWSrobot oh yeah?
15:59 veverak they are heavy
15:59 veverak but much cheaper on other side
15:59 AWSrobot nice, thank you
15:59 deshipu I want to experiment with some LiFePO4
15:59 deshipu veverak: you mean a Pb battery?
15:59 rue_house I have to experiment with liAl
15:59 veverak deshipu: yep
15:59 AWSrobot incidentally I just hooked this NiCd 15.6V into a power supply and charged it up to 17.4V
15:59 deshipu veverak: like in 1970s?
16:00 AWSrobot is that bad for it?
16:00 veverak deshipu: yeah...
16:00 rue_house or is it ALion?
16:00 rue_house Alion?
16:00 veverak I suppose Pb technology advanced too
16:00 veverak :)
16:00 rue_house no, lead acid is the same as always
16:00 deshipu dull and sour?
16:00 veverak :D
16:00 veverak I am just not sure still
16:01 veverak if it's good idea or not
16:01 veverak it's just that I won't mind more weight
16:01 deshipu just make sure you don't spill any ;)
16:01 rue_house lead acid is cheap
16:01 deshipu also easy to "fix"
16:15 deshipu AWSrobot: by the way, the rechargable NiCd/NiMH 1.2V batteries are fine too, if you don't care about the weight so much
16:21 rue_bed this->frameData.joint[i].axis[this->frameData.joint[i].count].count = 0;
16:21 rue_bed desp..
16:21 rue_bed gone
16:32 veverak lol
16:32 veverak that looks so ugly it's somehow sweet
16:32 veverak :D
18:28 LiohAu deshipu: I want to use this model for my robotic hand http://www.feetechrc.com/product/digital-servo/23kg-cm-high-torque-hv-metal-case-digital-car-servo-fi8625m/
18:30 LiohAu Since I'll need a servo motor controller with a lot of pins (more than 20 servos involved), what kind of board would you recommend?
18:30 SpeedEvil how much?
18:30 LiohAu 32$
18:30 LiohAu (each)
18:31 LiohAu SpeedEvil: talking about the price right?
18:33 LiohAu I'm looking at this board : http://www.robotshop.com/ca/en/sync32-servo-motor-controller.html - but i'm afraid that when the hand will clamp, all the servos will consume too much current
18:33 LiohAu on the feetech servo page it's written : "This servo can produce high-current draw from your batteries. If using NiMH or LiPo batteries, make sure they are capable of delivering approximately 2A for each servo."
18:38 LiohAu well I have to go :(
18:39 SpeedEvil The servo pwm lines use 0 current
18:39 SpeedEvil only the power wires use current
18:40 LiohAu yes, but it's the board that provides the power pin right?
18:40 LiohAu I mean the board has 3 pins, 1 for power, 1 for signal and the last one for the ground.
19:06 SpeedEvil There is no reason you can't wire teh servo power to another board
19:06 veverak yeah
19:06 veverak people usually power servos externally :)
19:07 SpeedEvil That board does mention 16A
19:08 SpeedEvil but if you need 20, then no, if you want to run them all at once - or be able to power on reliably - you will need >32
19:57 Guest91845 rue, you awake?
20:01 rue_house yea
20:01 _moon cool
20:01 _moon can i come over?
20:01 rue_house its moon!
20:01 _moon yeah
20:01 rue_house I got an ill stonach so I ant do much
20:02 rue_house stomach
20:02 _moon ooo
20:02 _moon :(
20:02 _moon well i wont then
20:02 _moon so i kinda got postgres working
20:02 rue_house "I got an ill "+spellcorrect("stomach")+" so I cant do much"
20:04 _moon *tummy = &stomach
20:04 rue_house so whats the postgres goal?
20:05 _moon umm
20:05 _moon well the first goal was reading and writing to a table with some webb based - ness
20:06 _moon html formz and php
20:09 rue_house should get familiar with it ont eh console first
20:22 _moon i was trying that
20:22 _moon i did set up the table in the console
20:22 _moon but that first goal is met now anyway
22:38 rue_house yay, my new libraries work