[REQ] motor?

Post by **sharky** » Wed Mar 26, 2008 5:26 am

hi guys!

i have a motor. this motor needs to be driven and the only source i found has 15 V instead of 12. i dont know the consumption of the motor and since i do not have a proepr source i cant measure it. the motor resistance is 9.8 ohm.

check the image: if i run it for 20 seconds 3/4 times a day, is ther ea risk of burning trough it? i will be unter relativel yhigh torque

Post by **LukePC1** » Wed Mar 26, 2008 6:38 am

I'm not shure, if the resistance of the motor can be measured right, because of magnetism which can store energy as well.

Assumed your measurments are right (you'd have to measure for some time, so the value doesn't change anymore):

R= U/I --> I= U/R = 12V/10Ohm = 1,2A
P= U*I = 12V*1,2A = 14,4W
Your motor has 14,4W

Supply:
P= U*I = 15V*3A = 45W = 45VA

Your supply is strong enough, to provide much more energy (about 3 times as much), but the resistence should limit it to

15V*1,5A = 22,5W, which is 'only' 50% more

If you want to be shure you could add a resistor of about 5 Ohm:
15V/15 ohm = 1A --> then you are giving it to less power...

I don't know, how far a motor could be 'overpowerd' for such a short time, but LED's can be overpowered more than twice the current

Post by **sharky** » Wed Mar 26, 2008 7:40 am

yep 1,5 is exactly what i measured on the 15 V.. :)i hate resistors because they olways get so hot when they are attached to such devices...i have arobotics book i could check for the tension but dont know if i find what i am searching for.. anyway thnx for your help..

Post by **sharky** » Wed Mar 26, 2008 7:45 am

i found that normal motors can take -50% +40% of the voltage. but not for continuos usage.. only short periods.. so i should be safe. the range for this motor qould be 6-16 V.

Post by **crim3** » Wed Mar 26, 2008 12:01 pm

Why don't you use a PC power supply? It's a good way of recycling them and you have auto regulated 12V and 5V.

Post by **sharky** » Wed Mar 26, 2008 12:46 pm

because i dont have one..

Post by **crim3** » Wed Mar 26, 2008 2:11 pm

ops! I was supposing that everybody has several pc power supplies from old computers. I can't throw them to the trash without feeling sorry so I keep them like a maniac.

Post by **sharky** » Wed Mar 26, 2008 4:31 pm

heh i never throw a pc away.. i always sold them..

moreover there is the security to bridge in them. the "signal" line dneeds to be bridged, and some PSU have no output under a minimal consumption.

Post by **nubie** » Wed Mar 26, 2008 6:12 pm

Is that from a car?

If so I wouldn't worry about it, car charging systems are supposed to hold the voltage close to 14 volts anyway, and 1 volt more won't hurt it.

Post by **sharky** » Thu Mar 27, 2008 2:08 am

yep car..

Post by **LukePC1** » Thu Mar 27, 2008 4:24 am

OK nice. Now you have a working motor with a considerable power, what do you want do do with it? Have you found a way, to power the hydraulic chair with it? The simulator chair thing, mentioned before?

Or is 15W too little to do it?

15W = 15Nm/s --> it could pull a 75kg person = 750N a little up.
heighth = 15Nm/750N = 1/50m per second --> that is 2cm per second

Seems not to be that much

Post by **sharky** » Thu Mar 27, 2008 6:46 am

i have 2 plans.. first a rollinf system, second the chair.

for the chair i have a motor with 30% more power, and it does not have to lift, but onlybend the chair backwards..

should be enough for a 120 kg person..

Post by **LukePC1** » Thu Mar 27, 2008 7:05 am

I'm not shure, if you can calculate here.
It depends on how you 'push' against the lean of the chair i.e. against the direction of the motor, if it will work ok.

I just calculated something around. Maybe your chair will move 5cm/sec or maybe 10cm...
I don't know, if that is fast enough.
Maybe it won't do anything, because the human is stronger

Post by **sharky** » Thu Mar 27, 2008 9:34 am

well i use a wispermotor, with a drastic reduction..

it moves back/forward, and it can reach the 2 extreme positions in one second. i dont need to use the whole distance. i can use simply a smaller angle with a pot,but it should me much more then enough powerfull to throw me off the chair..

when my father sits on the chair (130 kg) i can bend the chair with the little finger.. im afraid it will throw my father too against the wall..

Post by **wuhlei** » Thu Mar 27, 2008 10:38 am

lol make sure you record it if you test it.

Post by **sharky** » Fri Mar 28, 2008 2:10 am

thats for shure.. but first i need to program it.. i have soume troubels (even before starting) in making it usb compatible. i might use the printer port, but that has downsides too. unfortunately usb needs to recognize the attached device... printer port is slow. has a 55 ms response. i would need 10 ms..i could use some system dlls to speed it up, but i dont like that.

Post by **LukePC1** » Sat Mar 29, 2008 4:27 am

50ms delay is 1/20th of a second, so you would get nearly 20 'fps'. If you sped up things by a factor of 2, you might have enough speed...

On top of that, I'm not shure, how fast the motor can react anyway

Post by **sharky** » Sat Mar 29, 2008 4:39 am

well, the speed is not related to the motor.. because that depends on the motor power. this speed is only how many different positions i send out. i want to send 10 signals / second that is not aproblem for the printer port. i hope that 100 ms is fast/slow enough. i have no idea what a good value could be. trough the printerport i cant use the PWM solution because it is too slow, so i hav eto make a binary conversion in order to have a according voltage/position for the motor. basically i have to compare the output from the printer port with the signal from the potty.

Post by **Likay** » Sat Mar 29, 2008 6:35 pm

For the rool infeed i think you can use quite simple external electronics for the control of it. The extra power is of no trouble for the engine if you plan to run it for a few seconds at a time. 5-10 minutes with 15 volts should be no problem either but keep you nose close to it if testing.

cheers

Post by **sharky** » Mon Mar 31, 2008 12:10 am

any idea of a chip that does parallel to PWM conversion? i only know about the BS2, but its 85 euro and i have to program it myself...