Banebots RS-775 Case Short

[Mr. Lim]

...I know on 1114 we'll be giving these motors another chance...

At least 4 losses could be directly attributable to case shorted 775s during our 2011 season. We tested them all prior to competition season. A short developed throughout Waterloo and ultimately started causing problems in GTR.

Even though checking the resistance between every match got us through Champs, we had to "blast" them 3-4 times, each time holding our breath hoping that it would work.

We got lucky... it worked every time.

A year off for the 775s is the plan so far for us. If we're forced to us them, they'll be completely electrically isolated. Plastic mounts, and 1st stage gearing.

[Ether]

Originally Posted by artdutra04

Edit: If Banebots did supposedly switch to a new supplier, I'm wondering if these are the remainder of old motors from last year they had in stock?

Well that was really what I was getting at. How many freight cars of these things do they have in inventory. Maybe they're selling the new ones to non-FRC customers. Sorry to be so cynical.

[PAR_WIG1350]

Originally Posted by Karthik

I know on 1114 we'll be giving these motors another chance, but at the first sign of trouble they'll be introduced to our arbor press.

Your going to crush them? If you do, can you post pictures/a video? On a side note, it would be cool to see a motor cut along its axis bisecting the shaft and case .

[Dale(294engr]]

Originally Posted by MattC9

Hmmmm.... Just our luck I went and checked our 3, 2 of which were conductive. What exactly makes them "bad"? I have not heard why exactly this a problem.

This is a mfr defect carryover from last year. Appears Banebots may be dumping known defective 775's on FIRST as I and others contacted Banebots
but they resisted acknowledging there was a problem.
I personally performed failure analysis, witnessed shorted turns to rotor core.

RS-775 rotors use epoxy coated core laminations as insulation, ineffectively.

(most motors use brown fiber insulation. check out CIM rotor. Epoxy, properly quality controlled, MAY allow a more compact motor & less labor to mfr)

Enamel windings short at iron lamination corners via break thru at tight bend.

Two windings shorted behaves as a shorted transformer winding
causing no load motor current to quickly increase, depriving motor of torque

if short to motor case = robot AL frame, it is Illegal and failed at inspection

(theoretical remedy: electrically isolate each motor to pass inspection, but problem will likely escalate as more turns shorted draws higher current & produces less torque; high localized heating leads to catastrophic smoke)

Shorts I measured were typically ~0.1 ohm to case (either terminal to case)
which requires a careful low ohm set-up

It's a smoking gun again this year.. This is a great well made motor otherwise.
PreTesting out of new box is essential if decision to use these.
At a regional last year 70% of new boxed spare parts 775's were shorted!

causing huge delays for teams counting on them (Team 207 et al)

[Al Skierkiewicz]

Adding to Dale's post...
The epoxy coating in and of itself cannot protect this problem from occurring. The vibration of the motor turning, heat cycling during operation and movement within the windings will eventually break through the enamel coating used to insulate the motor wires. The breakdown at the very least will cause the case short and as stated as more windings breakdown, current flows through the armature and from the armature to the case. As heat builds up for these conditions, further deterioration will occur robbing motor power and drawing higher currents. Sorry guys, I thought Banebots had solved the issue and it was behind us.

[MrForbes]

Originally Posted by Ian Curtis

If all the Styrofoam is in the box, how do you know BB is at fault? Shipping companies don't intentionally damage goods, but they move a truly monumental number of packages and occasionally stuff gets dropped/run-over/what have you.

Exactly....the sender is responsible for packing the items sufficiently well to prevent damage under typical shipper handling.

I encounter this problem a lot when buying stuff on ebay, not many people know how to pack stuff. The most important thing is to not leave any empty space in the box, if the items are relatively heavy. Motors are heavy, the box needed to be filled with packing material, not air.

[SM987]

Just tested ours; one out of five was shorted. Disappeared after a zap, but it will be our worst case scenario backup.

[JesseK]

Ever since the 550's got their plastic fins to push air, they hold up much better than they used to. I'd seriously reconsider ignoring them altogether.

Early adopters: either they're the bird that gets the worm, or they're the worm that gets eaten by the bird!

[Chris is me]

Originally Posted by JesseK

Ever since the 550's got their plastic fins to push air, they hold up much better than they used to. I'd seriously reconsider ignoring them altogether.

I'm just saying how can you trust the Banebots brand when they are practically synonymous with poor quality control? AndyMark has much better service than them, so I'm going to use all AndyMark motors on my robot. Seems simple to me.

[jason701802]

Originally Posted by Dale(294engr]

(most motors use brown fiber insulation. check out CIM rotor. Epoxy, properly quality controlled, MAY allow a more compact motor & less labor to mfr)

That may be true of large industrial motors, but just look at all the other 300, 500, and 700 series motors in the kit and in other places, they almost exclusively use enamel coated wire. This is especially true of RC car motors, most of which are higher current than any that come in the kit and are 500 series motors.

Even the van door motor and the CIM that I've taken apart have used enamel wire, admittedly it was an old CIM. I don't think any motors in the KOP use fiber wire insulation, and I'd very much like to see one that does.

[Al Skierkiewicz]

Jason,
The OP is referring to insulation between the enameled wire and the armature. It has different names but the effect is to protect the corners. Using enameled wire is virtually the only way to efficiently develop a magnetic field with the minimum amount of wire.

[jason701802]

Al,
That makes a lot more sense, but I still don't think it's as common as he claims, most motors I've torn apart just use a nice think layer of enamel.

[waialua359]

We got several that came in the other day and we have the same problem with ours as well.
This is/may be the first time we use Banebots this season.
We never touched them before ever since they had the transmission issues in their inaugural year being in the FIRST kit of parts.

[Karthik]

Originally Posted by Karthik

I know on 1114 we'll be giving these motors another chance, but at the first sign of trouble they'll be introduced to our arbor press.

Four brand new motors arrived today. All shorted. I'd call this the first sign of trouble...

http://desmond.yfrog.com/Himg736/sca...=640&ysize=640

We will not be using any RS-775 motors this year.

Originally Posted by Karthik

Four brand new motors arrived today. All shorted. I'd call this the first sign of trouble...

http://desmond.yfrog.com/Himg736/sca...=640&ysize=640

We will not be using any RS-775 motors this year.

This just made my day!