10-02-2011 00:58

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 00:59

Aren_Hill

Re: pic: In_CIM_erator

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

10-02-2011 01:10

Justin Montois

Re: pic: In_CIM_erator

lol I'm quite sure they did.

10-02-2011 01:24

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 01:26

Aren_Hill

Re: pic: In_CIM_erator

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

10-02-2011 01:36

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 01:56

AdamHeard

Re: pic: In_CIM_erator

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.

10-02-2011 02:00

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 02:10

AdamHeard

Re: pic: In_CIM_erator

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.

10-02-2011 02:13

John G

Re: pic: In_CIM_erator

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

10-02-2011 02:17

AdamHeard

Re: pic: In_CIM_erator

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.

10-02-2011 02:18

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 02:22

John G

Re: pic: In_CIM_erator

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.

10-02-2011 02:32

ttakashima

Re: pic: In_CIM_erator

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

10-02-2011 02:40

Hawiian Cadder

Re: pic: In_CIM_erator

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

10-02-2011 02:43

rahilm

Re: pic: In_CIM_erator

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.

10-02-2011 02:54

Hawiian Cadder

Re: pic: In_CIM_erator

you are correct, my mistake

i still think it warrants closer inspection however.

10-02-2011 03:34

Tristan Lall

Re: pic: In_CIM_erator

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.

10-02-2011 07:02

martin417

Re: pic: In_CIM_erator

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.

10-02-2011 07:59

Jared Russell

Re: pic: In_CIM_erator

I can tell you that the RS775s are much closer to the CIM's max power than to the RS550's. We had been using 6 CIMs in our drive prior to receiving our CIM-U-LATORs, and the pushing power and acceleration with 2 CIMs replaced by RS775s are pretty close to identical.

10-02-2011 08:03

Chris is me

Re: pic: In_CIM_erator

The 18v RS775s at 12v are not "a measly 70 watts" - Banebot's spec sheet even says otherwise (just not FIRST's, which is wrong).

Hawaiian CADer, I've corrected you on this at least 3 times - for the sake of other teams PLEASE do not post things you don't KNOW to be true as fact, repeatedly, lest you cost someone valuable time in their season.

Be aware that Max Efficiency is different than Max Power.

10-02-2011 08:11

Vikesrock

Re: pic: In_CIM_erator

The Motor Curves document on the Kit of Parts website has been updated and contains the proper curve for the RS775-18V scaled down to 12V.

10-02-2011 18:34

artdutra04

Re: pic: In_CIM_erator

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.

10-02-2011 20:44

Tom Line

Re: pic: In_CIM_erator

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...

10-02-2011 22:30

Hawiian Cadder

Re: pic: In_CIM_erator

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.

10-02-2011 23:10

kevin.li.rit

Re: pic: In_CIM_erator

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.

10-02-2011 23:18

kevin.li.rit

Re: pic: In_CIM_erator

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

10-02-2011 23:26

Chris is me

Re: pic: In_CIM_erator

things such as free speed come into play too.

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

10-02-2011 23:53

Tristan Lall

Re: pic: In_CIM_erator

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).

11-02-2011 00:17

Hawiian Cadder

Re: pic: In_CIM_erator

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

11-02-2011 00:38

kevin.li.rit

Re: pic: In_CIM_erator

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

11-02-2011 01:14

Hawiian Cadder

Re: pic: In_CIM_erator

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.

11-02-2011 01:21

AdamHeard

Re: pic: In_CIM_erator

This is not proof whatsoever.

I see no reason to not trust the banebots specs.

11-02-2011 01:23

Hawiian Cadder

Re: pic: In_CIM_erator

ok, but i recommend you turn one on at the least, compare it to the RS-550.

11-02-2011 01:27

Akash Rastogi

Re: pic: In_CIM_erator

Hawiian Cadder- It is amusing that you are continuously questioning the intelligence of Adam as well as team 33, among others. while they try to explain to you your errors.

I am pretty sure Adam has turned on one of the motors 5 weeks into build...

11-02-2011 01:35

sanddrag

Re: pic: In_CIM_erator

Also, on the "thumb test" the 775 shaft is significantly larger than the 550 shaft. You're able to get a much better grip on it, and apply more torque to it.

Not at all scientific nor conclusive.

11-02-2011 01:45

Hawiian Cadder

Re: pic: In_CIM_erator

i made a hub out of delrin which press fit onto the rs 775 axle, on the other side it pressed onto the rs550 axle, they were both the same delrin drum which was tested.

11-02-2011 01:46

AdamHeard

Re: pic: In_CIM_erator

I got a test for ya, a good ol drag race.

Lock the shafts of the two motors together, and run them opposite directions. Whichever doesn't die is the winner!

11-02-2011 01:58

Hawiian Cadder

Re: pic: In_CIM_erator

i was planning on making my delrin hub into a pulley tomorrow and see which motor will lift a little weight the fastest, we are not using either of the kit motors either so i may try a drag race, that will likely fry one or both of the motors though.

11-02-2011 02:02

Andy A.

Re: pic: In_CIM_erator

95 used the banebots published spec sheet to design a shoulder joint. It is operating as intended, which I would not expect to be the case if the actual motor performance and the specified performance differed by such a wide margin. Given the frictional loses we're undoubtly encountering it's a little surprising that it's performing as well as it is, truth be told. We were conservative and planned on using two of these motors ganged together, but are finding out it operates just fine on one. We'll likely use the second anyways but I wouldn't be surprised to find out the motor is operating a bit above the projected rating.

In fact, not only is it operating spot on at the design speed, it is holding level a pretty substantial arm for ~10 seconds (stalled at about 15 amps maybe) with no apparent heat issues. I'm petrified of holding any longer then that right now, but I suspect it could do it. That places it well above the FP motor in my book on the size/weight/power/reliability value matrix.

Whatever the actual performance is it's way closer to the banebots published spec then it is to 70 watts.

11-02-2011 02:07

kevin.li.rit

Re: pic: In_CIM_erator

You should do a series of weights until you reach stall that way you can find peak power. You should also use a power supply to control the voltage if possible.

14-02-2011 00:30

Tom Line

Re: pic: In_CIM_erator

We engineered a component on our robot using the R775. We knew the weight, and using the calculated power of the R775 we figured it would take: 0.8 seconds to traverse the distance we needed. It performed exactly as it was engineered to, and the R775 provided the exact amount of power that it was supposed to.

I have absolutely no reason to doubt the manufacturer's specifications on these motors. They appear to be correct.

15-03-2011 17:16

Ether

Re: pic: In_CIM_erator

Just discovered this thread. From the vantage point of a month later, I suppose it is possible that Hawiian Cadder was using a defective RS775. Do you still have that motor? Do you have another RS775 you could compare it to with your "thumb test"?

A few additional remarks. Peak output power occurs at half free speed, not at stall (post #42), and not at the intersection of the torque and speed curves (unless the graph is scaled to make it so) (post #17). Kv (rpm/sec) is the velocity constant, not the motor constant. Motor constant is Km which is (stall torque)/sqrt(input watts at stall) (post #27).

16-03-2011 01:16

Creator Mat

Re: pic: In_CIM_erator

Another thing just take a look at the motors. I know this is a tad unscientific but doesn't a bigger motor generally = more power? Plus ask yourself if a manufacturer made a smaller lighter motor that was more powerful than a bigger heavier motor why would they make the bigger motor in the first place? So why is it not so off base to conclude that the RS 775 18v is more powerful than the RS 550 motor? Especially when the manufacturer's specs back up this idea.

16-03-2011 01:20

EricH

Re: pic: In_CIM_erator

Bigger motors only have more power if they aren't case shorted half the time or more.

Guess which motor has a tendency to have a case short?

16-03-2011 02:58

Chris is me

Re: pic: In_CIM_erator

How does that add to the discussion about the 775's peak power?

The 550s have other reliability issues, just more obvious and less damning (i.e. trying to stall them will quickly result in smoke, while the 775s can take more abuse. when the case isn't shorted.)

02-04-2011 11:00

Tristan Lall

Re: pic: In_CIM_erator

Just to resurrect the discussion about whether the 18 V RS-775 motor from BaneBots (M7-RS775-18) is a Mabuchi product, see here and here for what a Mabuchi sold by a reseller looks like. You can clearly see the differences in case style from the Mabuchi spec sheet, and if you look closely at the first link, you can also pick up the (painted-on) Mabuchi "M" logo on the side of the case, with what appears to be a part number underneath the reseller's label.

So I stand by my contention that the Banebots RS-775 from 2011 is not a Mabuchi motor.