#robotics Logs

May 02 2018

09:41 AM veverak: fuck this shit
09:44 AM veverak: so, I burned mosfets on Sabertooth 2x5A
09:44 AM veverak: question is, HOW THE HELL?
09:44 AM veverak: it's suppose to have overcurrent protection and shit
09:44 AM veverak: the battery polarity was OK, and yet after connection to BUT I've got black smell
09:44 AM veverak: burned both mosfest for one motor
10:52 AM AchiestDragon: mosfets are suposed to go high resistance on over temp , thats there inherant overcurrent protection , its not true mesured over cutternt protection , ther not easy to burn out but it is posible
10:53 AM SpeedEvil: MOSFETs do not go high resistance on overtemp.
10:53 AM SpeedEvil: Or rather - they do - but in such a way that their internal resistance maybe doubles.
10:53 AM SpeedEvil: This does not help at all.
10:54 AM SpeedEvil: (if you are using them in their normal switching role)
10:54 AM AchiestDragon: its 4 mosfets per motor, one for each side , if thers a short on the bord and both mosfets at one side of the H bridge are on that can cause 2 of them to fail
10:55 AM veverak: hmm, this burned 1/2 of each dual channel mosfet
10:55 AM veverak: somehow
10:55 AM veverak: thing is, somebody installed capacitors at the DC motors
10:55 AM AchiestDragon: if its one mosfet on each side of the h bridge then that is usualy down to a motor short ( or motor wire short )
10:55 AM veverak: however, in a way, that allowed it to accidentaly shortcut
10:55 AM veverak: I do believe, that the wiring to the motor shortcutted
10:55 AM veverak: and only half of each dual channel mosfet burned
10:58 AM AchiestDragon: yea the modern ones dont go as high resitance on over temp as the older ones , the ones i used to work on in audio amps did and thats how they got thre reputation over transistors like 2n3055 s that used to blow go short and take out most of the driver transistors in the process
10:58 AM veverak: FDS6911 to be precise
11:02 AM AchiestDragon: my old hbridge design https://drive.google.com/file/d/1LUsIeFpBzl_fF4G1x5e7e3xVc1HVVNmO/view?usp=sharing the parts are smd , but use bc547c npn bc557 pnp and irf640 irf9640 's for though hole ,,, works the same , just in the process of making 18 of them for my hexipod
11:03 AM veverak: https://www.dimensionengineering.com/products/sabertooth2x5
11:03 AM veverak: this thing
11:14 AM AchiestDragon: 0.1uf caps on the motors ? used as noise suppressors , should not be a problem unless there faulty/shoring
11:15 AM veverak: well
11:15 AM veverak: they were installed in a way that allowed the wires of the cup to touch the metal motor
11:18 AM AchiestDragon: well that prob explains why
11:23 AM veverak: damn it
06:24 PM veverak: you know
06:24 PM veverak: the feeling
06:24 PM veverak: when you finish prototype of prototype of prototype
06:24 PM veverak: https://imgur.com/a/Iinskdn
06:26 PM Plazma_ is now known as Plazma
07:03 PM durrf: A+ good finished product imo
07:12 PM veverak: too hacky
07:12 PM veverak: needs 3d printed shelf
07:13 PM durrf: use a 3d pen to close off the back
07:13 PM veverak: you mean gluegun? :D
08:45 PM AchiestDragon: https://drive.google.com/file/d/1V3wL1RX5njt4pPuVwVrSkRo2QJGI-54g/view?usp=sharing
08:46 PM durrf: gonna put a chair on top?
08:46 PM zhanx: dont think its needed
08:46 PM durrf: unicycle seat
08:46 PM zhanx: machine gun
08:47 PM durrf: you can put the machine gun under the seat
08:47 PM AchiestDragon: no theres still a turret and head to print , but on with the electroincs for the time
08:47 PM durrf: integrated seat warmer :)
08:47 PM durrf: that is really cool
08:48 PM zhanx: but can it bring me a towel or make waffles?
08:49 PM AchiestDragon: turret with twin miniguns , if you want waffles with holes in maybe
08:51 PM AchiestDragon: although my contain traces of bb's
08:51 PM zhanx: still nice worl
08:51 PM zhanx: work*
08:52 PM zhanx: like your motor to screws idea
08:56 PM AchiestDragon: ive put the files on github , although the software is still work in progress https://github.com/achiestdragon/leggie
09:21 PM zhanx: cool thanks AchiestDragon i will follow it, its a bit larger than my bot I made a few years back
09:22 PM zhanx: https://hackaday.com/2010/02/11/veteran-robot-features-eight-legs-and-beagleboard/
09:23 PM zhanx: gonna 3d print and make it again one day