pic: In_CIM_erator

[John G]

Originally Posted by AdamHeard

I think you're confused a bit. Motors are spec'd at a voltage, but will run at any voltage (although, they won't last long once you hit a certain voltage).

A motor rated for 18V will run fine on 12V, it will just be roughly 4/9 the power of it on 18V.

Where did the 4/9 come from. I must have missed something in my math.

[AdamHeard]

Originally Posted by John G

Where did the 4/9 come from. I must have missed something in my math.

Mechanical power is torque x speed.

Stepping down from 18 to 12V is a 2/3 change.

Power = 2/3Torque x 2/3 speed. Works out to the power at 12V being 4/9 that of 18V.

[Hawiian Cadder]

none of the motor specs on the maubichi sheet indicate a power rating of more than 200 watts at 18 volts. thus i dont think it is possible for the 775's to output more than 133 watts MAXIMIUM negating friction.

[ttakashima]

Originally Posted by Hawiian Cadder

none of the motor specs on the maubichi sheet indicate a power rating of more than 200 watts at 18 volts. thus i dont think it is possible for the 775's to output more than 133 watts MAXIMIUM negating friction.

the 18v - RS775 WC version is supposed to output 273.03 W of power at max eff. - 18v
the 18v - RS775 VC Version outputs 208 W or power at max eff. - 18v

here is the spec sheet are ya looking at this one?

The 775 VC outputs 41.4 W at 12v - 5.7A and 775 VC outputs 156 W at 12v - 18.7A

the 775 WC outputs 168 W at 12v - 18.7A and 775 WC outputs 39.9 W at 12v - 5.7A

[Hawiian Cadder]

the Series of Motors are only rated for 200 watts total, which leads me to believe that have quite a bad bias, (they are for drills after all) and i do not believe that those are the motors we have, the smaller rs775 more closely matches what we were supplied, if the Bane-bots 12v is one of those, but at 12v, then it will be a different size physically, the smaller series of motors here: http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_755vcwc


and 4/9 times 270 is 120. however efficiency also drops as current/voltage rises, so that puts the motor at somewhere around 90-110 watts.


Edit

The Bane bots motors are the smaller of the two motor spec sheets i initialy gave, verified by physical size. spec sheet here

http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_755vcwc

[artdutra04]

Originally Posted by Hawiian Cadder

the Series of Motors are only rated for 200 watts total, which leads me to believe that have quite a bad bias, (they are for drills after all) and i do not believe that those are the motors we have, the smaller rs775 more closely matches what we were supplied, if the Bane-bots 12v is one of those, but at 12v, then it will be a different size physically, the smaller series of motors here: http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_755vcwc


and 4/9 times 270 is 120. however efficiency also drops as current/voltage rises, so that puts the motor at somewhere around 90-110 watts.


Edit

The Bane bots motors are the smaller of the two motor spec sheets i initialy gave, verified by physical size. spec sheet here

http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_755vcwc

I wanted a definite answer on this, so I began searching further to try to find the original source of the BaneBot RS775-18 motors. While I don't have access to a BaneBot motor to peel the sticker off of, I did find this clear image of the 775 motors:

http://www.chiefdelphi.com/media/photos/36263

In the full-resolution version of the photo, two things are obvious: The last four numbers on the first line are "8514" and the last two letters on the second line end in "CW". On the Mabuchi website, they do sell a "775WC" motor with the part number "8514". These published specs at 18V match the published specs (for 18V operation) on BaneBots' website. The likely reason behind the letters printed on the BaneBot motors being in the wrong order are due to the fact that Manuchi is a Japanese company, and the BB motors were all made in China (possibly by a clone manufacturer).

So the Mabuchi specs list the power of the Mabuchi 8514 at peak efficiency as 273 W. The BaneBot spec sheet for their RS775-18 at 12V lists power at peak efficiency as 119.25 W. If they are the same motor, then 273W * (4/9) = 121.33 W would yield the expected power output at 12V. The expected and actual power values are only 1.7% off; if BB published their RS775-18 at 12V spec sheet from dynamometer testing, this 1.7% likely could have been due entirely to manufacturing tolerances of the 775 motors.

Thus, unless someone has dynamometer data to prove otherwise, these specs for the RS775 are accurate.

[Tom Line]

Originally Posted by artdutra04

I wanted a definite answer on this, so I began searching further to try to find the original source of the BaneBot RS775-18 motors. While I don't have access to a BaneBot motor to peel the sticker off of, I did find this clear image of the 775 motors:

http://www.chiefdelphi.com/media/photos/36263

In the full-resolution version of the photo, two things are obvious: The last four numbers on the first line are "8514" and the last two letters on the second line end in "CW". On the Mabuchi website, they do sell a "775WC" motor with the part number "8514". These published specs at 18V match the published specs (for 18V operation) on BaneBots' website. The likely reason behind the letters printed on the BaneBot motors being in the wrong order are due to the fact that Manuchi is a Japanese company, and the BB motors were all made in China (possibly by a clone manufacturer).

So the Mabuchi specs list the power of the Mabuchi 8514 at peak efficiency as 273 W. The BaneBot spec sheet for their RS775-18 at 12V lists power at peak efficiency as 119.25 W. If they are the same motor, then 273W * (4/9) = 121.33 W would yield the expected power output at 12V. The expected and actual power values are only 1.7% off; if BB published their RS775-18 at 12V spec sheet from dynamometer testing, this 1.7% likely could have been due entirely to manufacturing tolerances of the 775 motors.

Thus, unless someone has dynamometer data to prove otherwise, these specs for the RS775 are accurate.

And following that graph, at about 40 amps, the motors put out approximately 260 Watts of power unless I've been reading it wrong all season...

[Hawiian Cadder]

to eliminate all of the spec sheet madness from this, i decided on a simple test, today i made a small hub that pressed onto the axle of the 775 and had a .5 inch diameter, hooked the motor directly to a battery, and was able to prevent it from spinning with no problem at all. i did the exact same thing with a 555 and have a rather nasty burn on my thumb from trying to hold the motor and failing. the rs550 is significantly more powerful than the rs775 18 volt version that came in the KOP.

edit for clarification

i let both spin up to full speed, then attempted to stop them spinning by gradualy applying pressure to the outsides of the .5 drum. both motors were mounted to a block, and that block placed in a vice, and both were running off direct connection to battery with the same length of wire.

[kevin.li.rit]

Wouldn't looking at he motor constant (Rpm/V) values tell you that the motors perform differently and they are two different motors with he same package.

[kevin.li.rit]

Originally Posted by Hawiian Cadder

to eliminate all of the spec sheet madness from this, i decided on a simple test, today i made a small hub that pressed onto the axle of the 775 and had a .5 inch diameter, hooked the motor directly to a battery, and was able to prevent it from spinning with no problem at all. i did the exact same thing with a 555 and have a rather nasty burn on my thumb from trying to hold the motor and failing. the rs550 is significantly more powerful than the rs775 18 volt version that came in the KOP.

edit for clarification

i let both spin up to full speed, then attempted to stop them spinning by gradualy applying pressure to the outsides of the .5 drum. both motors were mounted to a block, and that block placed in a vice, and both were running off direct connection to battery with the same length of wire.

This isn't an accurate test of the motors power output but rather the stall torque.

[Chris is me]

Originally Posted by Coffeeism

This isn't an accurate test of the motors power output but rather the stall torque.

things such as free speed come into play too.

you're really going to refute manufacturer provided dynamometer specs with a thumb test?

[Tristan Lall]

Speaking of Mabuchi, my guess is that the BaneBots RS-775 motors are not made by them...see http://www.chiefdelphi.com/media/photos/36278 and look closely at the motor, and then at the drawing posted on Mabuchi's website. Observe the shape of the rear vent holes is different. While that's not conclusive proof of anything, it's a reason to doubt that the BB RS-775 is that particular Mabuchi model. (I've seen another pattern, with no vent holes, on some Mabuchi motors; that isn't it.)

As far as I know, none of BaneBots' KOP motors are made by Johnson or Mabuchi. The best refutation of this would be to find their logo: Johnson often stamps a "JE" mark on the front face of the motor (where the mounting screws are), and Mabuchi usually prints a stylized "M" on the label (they haven't used painted numbers on FRC motors in the past).

[Hawiian Cadder]

if the rs550 had more torque at a higher speed doesn't that mean it has more power?

[kevin.li.rit]

Originally Posted by Hawiian Cadder

if the rs550 had more torque at a higher speed doesn't that mean it has more power?

Yes but none of the specs support this and your thumb test did not appear to measure speed.

[Hawiian Cadder]

thumb test = slowly apply load until motor stalls, rs550 gave me a burn because it didn't stall. rs775, stalled very easily. this is in contradiction to the spec sheets, and based on discrepancy between spec sheets i think teams should actually run the motors to see how much power they actual give off, we don't have a dyno, but someone who does can measure power.