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
lol I’m quite sure they did.
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.
here is the link to the actual source of the motors, BaneBots Buys them from here, and according to this spec sheet
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.
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.
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.
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.
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.
Ok. I did Power = w/t; w = Fd; F = torque *r. I thought distance and time would stay constant, so I ended up with 2/3 by just changing the torque. Thank you.
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
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-bin/catalog/e_catalog.cgi?CAT_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.
The Bane bots motors are the smaller of the two motor spec sheets i initialy gave, verified by physical size. spec sheet here
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.
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.
Just curious about how you measured the power of the 775 vs the 550. Did you use a dynamometer? Or did you use the motors in a lifting application with a gearbox? Did you compare the work done over time?
The only info I have to go on is the motor curve provided by FRC, and the data sheet on the Banebots website. If you look at the data for the 18V motor, it maps pretty well to the FRC motor curve when run at 12V instead of 18V. I have to believe the FRC motor curve since we based our design on that. We won’t know until we get our gearboxes, maybe next week.