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[Jim Zondag]

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[Hawiian Cadder]

did you look at the specs for those rs775's at 12 volts, at 18 volts they are pretty good, but at 12 volts they produce a measly 70 watts.

[Aren_Hill]

Originally Posted by Hawiian Cadder

did you look at the specs for those rs775's at 12 volts, at 18 volts they are pretty good, but at 12 volts they produce a measly 70 watts.

The 12v VERSION at 12v produces the measly 70 watts,

The 18v VERSION at 12v produces much more than that

http://banebots.com/docs/M7-RS775-18-AT12V.pdf

[Justin Montois]

Originally Posted by Hawiian Cadder

did you look at the specs for those rs775's at 12 volts, at 18 volts they are pretty good, but at 12 volts they produce a measly 70 watts.

lol I'm quite sure they did.

[Hawiian Cadder]

pretty sure the 18 volt version is the same, we ran ours and found it MUCH weaker than the RS 550, if anything the 18v version should be weaker than the 12V version, the only difference is the gauge of wire.

[Aren_Hill]

Originally Posted by Hawiian Cadder

pretty sure the 18 volt version is the same, we ran ours and found it MUCH weaker than the RS 550, if anything the 18v version should be weaker than the 12V version, the only difference is the gauge of wire.

Any quantitative tests? lifting a load, dynamometer...those spec sheets don't magically appear out of thin air.

[Hawiian Cadder]

here is the link to the actual source of the motors, BaneBots Buys them from here, and according to this spec sheet

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

the "BaneBots rs775 at 12 volts" does somewhere barely above 200 watts at 14.4 volts. the 18 volt version does somewhere around 70.


I am fairly sure that the numbers on BaneBots website are inccorrect, they do match up with a larger motor from this supplier.

http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_775vcwc

this is the larger motor, but as you can see it is not sold in a 12 volt version, so the 70 watts is close to what this would produce at 12 volts as well, none of the Mabuchi specs come even close to the BaneBots specs.

[AdamHeard]

Originally Posted by Hawiian Cadder

here is the link to the actual source of the motors, BaneBots Buys them from here, and according to this spec sheet

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

the "BaneBots rs775 at 12 volts" does somewhere barely above 200 watts at 14.4 volts. the 18 volt version does somewhere around 70.


I am fairly sure that the numbers on BaneBots website are inccorrect, they do match up with a larger motor from this supplier.

http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_775vcwc

this is the larger motor, but as you can see it is not sold in a 12 volt version, so the 70 watts is close to what this would produce at 12 volts as well, none of the Mabuchi specs come even close to the BaneBots specs.

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.

[Hawiian Cadder]

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.

i am aware, but (4/9) times to 200 watts max power that the supplier has tested for still leaves less than 100 watts of power, unless it is the 14.4 V nominal opperation motor, in which case it will output around 70 watts. according to the people who made the motors, there is no way any of them that size will output more than 100 watts at 12 volts.



also, power is current * Voltage

according to the Bane Bots website peak efficency current is 5.7

5.7 * 12 is 68, which fits the 70 watt power output number, i think all the other info on the BaneBots website is correct, except the power calculation, think that was taken at 18 volts.

[AdamHeard]

Originally Posted by Hawiian Cadder

i am aware, but (4/9) times to 200 watts max power that the supplier has tested for still leaves less than 100 watts of power, unless it is the 14.4 V nominal opperation motor, in which case it will output around 70 watts. according to the people who made the motors, there is no way any of them that size will output more than 100 watts at 12 volts.



also, power is current * Voltage

according to the Bane Bots website peak efficency current is 5.7

5.7 * 12 is 68, which fits the 70 watt power output number, i think all the other info on the BaneBots website is correct, except the power calculation, think that was taken at 18 volts.

The mechanical output power can be calculated from torque times speed.

If you take the motor at half free speed, it is also at half stall torque, for the 775 this works out to over 250W of power.

[rahilm]

Originally Posted by Hawiian Cadder

also, power is current * Voltage

according to the Bane Bots website peak efficency current is 5.7

5.7 * 12 is 68, which fits the 70 watt power output number, i think all the other info on the BaneBots website is correct, except the power calculation, think that was taken at 18 volts.

First thing, peak power is NOT peak efficiency. If you look a motor curve, you will find that efficiency is maximized at a much lower current than where power is maximized (at the intersection of the torque and speed lines).

Also, if using the electrical values to calculate output torque, you have to multiple the electrical power value by the motor efficiency at that point.

[Hawiian Cadder]

Originally Posted by rahilm

First thing, peak power is NOT peak efficiency. If you look a motor curve, you will find that efficiency is maximized at a much lower current than where power is maximized (at the intersection of the torque and speed lines).

Also, if using the electrical values to calculate output torque, you have to multiple the electrical power value by the motor efficiency at that point.

you are correct, my mistake

i still think it warrants closer inspection however.

[Tristan Lall]

By the way, does anyone have documentation that BaneBots is using that particular RS-775 motor from Mabuchi? (I know there's a part number under the sticker affixed by BaneBots...I just haven't had the opportunity to look underneath and confirm it.) In the past, their motors appeared not to have been Mabuchi-brand.

(And just in case anyone is wondering, yes, this comes up all too often at inspection. Inspectors will often be noticing things like number and shape of vent holes and the colour of the plating on a motor, to quickly assess its legality.)

In fact, the same goes for the other BaneBots motors too. It would be instructive to publish a list of the manufacturers' real part numbers (to forestall future questions about which motor is which).

In 2009, BaneBots shipped totally different RS-550 and RS-385 motors to FIRST teams, despite presumably knowing that there was an FRC parts restriction (given that they were a supplier of KOP motors), and without updating their website to reflect the changes. Given that previous miscue, we probably ought to be cautious.

[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.