How "bad" are motors with "bad" stickers?

[ChrisH]

Originally Posted by ahecht

Check out the Q&A:
So apparently this is a special automotive meaning of BAD that doesn't mean what we think it does.

"BAD" may apply to the fit rather than the function or some other problem that would prevent their being used on a production line but has no impact on our usage.

If one of the mounting holes was off for example. We would just ream out the mating hole and it is no big deal. But that might not be an option on a production line that moves every few seconds. On a properly balanced line there is no time for rework like that, not to mention that modification might make it so a replacement that was made to the proper dimension would not fit properly later.

There are probably many ways for one of those motors to be "bad" without affecting the we they work in our application.

ChrisH

[CJO]

The FPs are vastly underrated by the FIRST community at large, but those of us who have bent 1.5"x1"x1/8" aluminum C-channel with them have great respect for them.

The FP motors are good as far as they go, however,

If we believe the specs, the FP motors are over 400W each. If this holds true, they are going to get hotter than Hades insummer if and when they stall or run under high torque.

sums them up quite nicely. During the nationals alone, we had to replace our FP motor 4 times, so, yes they have a lot of power, but I have literally seen copper melt out of the casings.

[ChrisH]

Originally Posted by CJO

The FP motors are good as far as they go, however, sums them up quite nicely. During the nationals alone, we had to replace our FP motor 4 times, so, yes they have a lot of power, but I have literally seen copper melt out of the casings.

Then you have been running them too hot or too slow. I design mechanisms to operate at 75% of free speed and 25% max torque. This leaves plenty of margin power (approximately 50%) and with the high rpms you get plenty of cooling air through the motors. By operating on the fast side of max power, when things bog down, you actually get an increase in power. BTW I learned this the hard way myself. I am ashamed at what I did to our poor little Van Door motors our first year. Talk about torture

ChrisH

[cdawzrd]

haha.

we used fp's for a winch to pull up last year. burnt out twice. verry smelly :-)

those FP's just aren't the greatest thing around...

[Joe Johnson]

Originally Posted by ChrisH

... I design mechanisms to operate at 75% of free speed and 25% max torque. This leaves plenty of margin power (approximately 50%) and with the high rpms you get plenty of cooling air through the motors. By operating on the fast side of max power, when things bog down, you actually get an increase in power....

ChrisH

I KNEW I liked you, ChrisH. Another great thing about designing your machanism to run on the fast side of the power parabola is that the efficiency is higher on that side. That means more power turned into spinning shafts, less into heat.

ANOTHER benefit is a controls benefit. It is much much easier to control something when its free speed is only 1/3 faster than its designed loaded speed. The controller can be must less critical because the arm or whatever will not 'over run' the controls if the load vanishs (e.g. you were lifting 40 lbs of tetras and you just dropped the stack).

Joe J.

[Joe Johnson]

As to the possible "BAD" labels, I don't know for sure, but I can guess.

In the auto industry, there are 1000's of specs that components have to meet, motors more than most. There are EMC specs, EMI specs, Speed, Torque, Hot, Cold, Current, Sound, dimensional stuff, and so on.

There are many many times, when an engineering change is made that affects a specific problem that is may be important to the proper function of the assembly used in a car but that does not change the function of the part by itself. For example, a grease may have to be changed in order to meet a new environmental regulation in an export market. Another example may be a change to a casting in order to clear a trim change by an OEM.

Bottom line, MOST engineering changes made to a motor would have no noticeable affect on the performance of the motor when used on a FIRST robot.

In many cases, the engineering change leaves some stock on pallets in some warehouse in the midwest. That is where I come in... ...If we can get these motors to FIRST and get enough of them to make a complete kit's worth, they end up in the Kit.

SO... ...the most likely reason for the "bad" on the motors is that there was an engineering change or some sort of sorting process needed make the system work but made no difference to FIRST and someone* convinced the motor supplier or the motor user to donate these motors to FIRST.

Joe J.

*Jim Zondag from the Killer Bees has become an expert at these type of situations in recent years. You can become an expert at this too -- PM me for details...