diy servo project
WARNING.. I AM JUST SPOUTING NUMBERS OUT MY ASS. THEY ARE PROBABLY ALL WRONG.
i had been eyeing these cool surplus gearmotors. you can never tell from the tiny pictures and the stats always are mostly useless, so i threw down the big $12 for 2. they arrived last week and they look like they just might be perfect. i cut all the 'extra business' off of them and they weigh in at 365grams. just the 18 gearmotors for a full robot will weigh 6.57 kilos! yowsa. if you have not guessed, this robot will be a bit bigger than the last one. i'm aiming for asimo size.
i was trying to figure out what the hell this motor was so that i could make some rough calculations for the motor controller. i think i found it and holy shit, this thing has got some power..
http://www.johnsonelectric.com/product/product_sheet/fect_sheet.php?ProdID=75--A
the 'm-' in 'm-Nm' apparently means milli.
so using the trusty torque converter site and those number (best torque case).. http://www.unitconversion.org/unit_converter/torque.html ((280.05m-Nm)/1000)*208 gearratio = 58.2504 Nm! a standard rc servo is around 50oz/in when run at 6vdc. 58.2504Nm in oz/in is.. 8248.95.. or 165 times more torque than a standard rc servo! a standard servo weight 37grams. so for about 10 times the weight, i get 165 times the torque. a standard servo is about 60rpm and this servo should run at 54rpm. so it seem 'fair'
so pretty close to a servo.. just much bigger. unfortunately.. power typically is not one of those linear things. i hear a standar servo will use 1 amp (which i crazy for how small their motors are) under full load, so 1amp*6vdc=6 watts. this puppy.. 46.8amp*14.4vdc=674 watts.. that spec says 327 and i have no idea why (just another thing i need to learn about motors). anyway.. that is some scary electrical business there.
the expensive robot servos..
http://www.hitecrcd.com/Servos/hs5995TG.htm
416 oz/in torque for 62 grams. so for 5.88 times the weight i get 20 times the torque.
in summary.. even if i end up only getting 1/2 the torque out of this gearmotor (because my motor controller will suck and these are optimal values anyway).. they should still kick out twice the torque per weight of the super expensive ass robot servos. mine will cost under $10 a piece (an a bunch of time of course), those cost $110. best of all my robot could qualify to fight asimo in a steel cage match (for charity of course).