Team 190 in the October Servo Magazine

[ahecht]

Team 190 was featured in the GeerHead column of this months Servo magazine. The article has lots of info on our holonomic drive system, our autonomous hanging in 2004, and our 2002 CVT. You can view the article below (click the pages to zoom):

http://servo.texterity.com/servo/200...ageviewer?pg=8
http://servo.texterity.com/servo/200...geviewer?pg=10
http://servo.texterity.com/servo/200...wer?pg=12&pm=1

[Ian Curtis]

Just opened my issue and saw it. Very interesting stuff about the drive train that totally rocked my 2005.

[sanddrag]

The part about "Get your motors built, get them on the robot" on the first page seems highly illegal to me. Especially the retiming part.

[Cory]

Originally Posted by sanddrag

The part about "Get your motors built, get them on the robot" on the first page seems highly illegal to me. Especially the retiming part.

FIRST made it legal to do stupid things to your motors this year... ie: drilling holes in them.

I have no idea why, but it's only a matter of time before someone gets hurt, or a serious accident occurs.

After checking the rules, changing the windings of the motors would appear to be illegal (assuming the reporter correctly described everything).

Excerpt from <R31>:

<R31> So that every robot’s maximum power level is the same, the motors in the kit may not be modified except
as follows:
• It is acceptable to modify the mounting brackets and/or other structural parts of the motors (output
shaft, housing, etc.) as long as the electrical system is not modified and the integral mechanical
system of the moving parts (bearings, bushings, worm gear output stages, etc.) is not changed or
removed.

[dlavery]

Originally Posted by sanddrag

The part about "Get your motors built, get them on the robot" on the first page seems highly illegal to me. Especially the retiming part.

That is correct. This is a clear violation of <R31>.

<R31> So that every robot's maximum power level is the same, the motors in the kit may not be modified except as follows:
-It is acceptable to modify the mounting brackets and/or other structural parts of the motors (output shaft, housing, etc.) as long as the electrical system is not modified and the integral mechanical system of the moving parts (bearings, bushings, worm gear output stages, etc.) is not changed or removed.
-The gearboxes for the Fisher-Price, and Globe motors are not considered "integral" and may be separated from the motors. FIRST will not provide replacements for parts that fail due to modification.
The intent is to allow teams to modify mounting tabs and the like, not to gain a weight reduction by potentially compromising the structural integrity of any motor.

Retiming of the motors is clearly a no-no (modifications of the electrical system are specifically prohibited). Turning down the case is clearly against the rules (the exact intent of the rule is even spelled out - and it is made clear that this practice is against the rule). Drilling holes in the case and adding fans to alter the airflow is a not a legal performance enhancement to the motors (it is not one of the permitted modifications to the motors).

-dave

[edit: yeah, Cory just saw the same rule]

[phrontist]

That kind of puts a damper on this thread.

[JamesBrown]

well it may be illegal but it is a truely fabulous drive system, It was just fun to watch it drive.

Also does any one have a video of 190 in 2004 that shows them for a whole match on the bar i couldnt find anything because most of the footage is of the match rather than of the bot, if some one could post a link to a video that would be great.

[ahecht]

A video of one of our matches is available at http://zansstuff.com/video/BAE05WPIquarter.wmv. Bandwidth is limited, so please download it to your computer to view.

The rules clearly stated that modifying the housing of the motors was legal, and this was all we did. All holes were drilled away from the magnets, and in no way affected the electrical or magnetic functioning of the motor. The article exaggerated the retiming aspect a bit. When the motors were dissassembled and reassembled, the alignment of the motor can and brush assembly had to be adjusted, which can advance or retard the timing. Our "retiming" consisted of me and another kid out in the snow with a tachometer running the motors forwards and backwards as we screwed them back together. This in no way modified the electrical system.

If FIRST wants to state in the rules next year that modifying the motor cans is illegal, they are free to. However, this past year's rules stated:

It is acceptable to modify the mounting brackets and/or other structural parts
of the motors (output shaft, housing, etc.) as long as the electrical system is
not modified and the integral mechanical system of the moving parts
(bearings, bushings, worm gear output stages, etc.) is not changed or removed.

No electrical components or moving parts were changed or removed. The thinning and drilling was designed to improve cooling, not reduce weight (and the turning was done only to remove the powder coating). Also, the statement about intent was released in a rule update long after our motors were modified, and it is somewhat unrealistic to expect us to buy a new set of CIM motors due to a distinction that was added after the build season started.

[Cory]

Originally Posted by dlavery

That is correct. This is a clear violation of <R31>.


Retiming of the motors is clearly a no-no (modifications of the electrical system are specifically prohibited). Turning down the case is clearly against the rules (the exact intent of the rule is even spelled out - and it is made clear that this practice is against the rule). Drilling holes in the case and adding fans to alter the airflow is a not a legal performance enhancement to the motors (it is not one of the permitted modifications to the motors).

-dave

[edit: yeah, Cory just saw the same rule]

Dave,

During inspector training at either Sacramento, or SVR, we were specifically told that teams were being allowed to modify the casing of the motors by drilling/cutting holes in it(this was a rule that was very recently updated, as I recall). I think there may even have been a picture in the printed out slideshow showing a casing that had been drilled out. I was shocked that this was the case, and questioned whether having gaping holes in a motor casing would constitute a safety hazard. We never ran into such a situation, fortunately.

[sanddrag]

Well, as long as we are still discussing it, didn't Dr. Joe post something a while back about opening and/or modifying the CIM motors? I seem to recall something about even just opening it and putting it back together can cause it to lose magnetic strength. And also wasn't there some sort of discussion about cooling, like how the color black has a higher thermal emissivity than a shiny metallic freshly turned surface? Of course I could be making this up (it's late and I'm tired) but I thought I recalled some past discussion of the sort.

For retiming, unless they were reset to factory timing, and adjustment I would deem illegal if I were an inspector (which I hope to be for 2006). Advancing the timing of a permanent magnet DC motor can significantly improve performance in the "forward" direction. Also, setting an advanced timed motor to neutral timing can significantly improve the "reverse" performance and balance things out. So, due to these modifications enhancing the performance of the motor, I would have to say it wouldn't be legal (unless set back to factory specs).

Also, I'm just curious: did you ever run any tests (real comparison data, not "I touched it and it wasn't warm") to see if the modifications you did helped or hurt performance and/or cooling? Also, was there a problem with CIM overheating to begin with, because I don't think that's an issue for too many teams. Was your application different than most?

[dlavery]

Originally Posted by sanddrag

Well, as long as we are still discussing it, didn't Dr. Joe post something a while back about opening and/or modifying the CIM motors? I seem to recall something about even just opening it and putting it back together can cause it to lose magnetic strength. And also wasn't there some sort of discussion about cooling, like how the color black has a higher thermal emissivity than a shiny metallic freshly turned surface? Of course I could be making this up (it's late and I'm tired) but I thought I recalled some past discussion of the sort.

You are recalling the warning from Joe Johnson correctly. The issue was briefly mentioned in this thread and this thread (and I think there was at least one other, more lengthy discussion somewhere else, but I can't find it right now). You can significantly reduce the field strength of the permanent magnets in the CIM motors if you remove the rotor without taking appropriate precautions. Unless you really know what you are doing, and are using appropriately sized keeper bars, you will want to leave the rotor alone and keep it right where it is.

-dave

[JVN]

Originally Posted by dlavery

I think there was at least one other, more lengthy discussion somewhere else, but I can't find it right now.

You are referring to this thread:
http://www.chiefdelphi.com/forums/sh...ad.php?t=33313

[ahecht]

Although we never hooked our CIMs up to a dynamometer, the no-load speed was the same before and after we removed and replaced the motor cans (before any metal was removed). We did see that tweaking the motor cans during reassembly can significantly alter the timing (you could both see this with the tach and hear it), so I am wondering if what Dr. Joe saw was simply a misalignment problem. Even he didn't have a real explanation as to why removing the can is bad, only:

don't take the armature out of the magnets -- again I have REAL DATA to show that you can lose as much as 10% of the output of the motor by simply taking the armature out of the housing and putting it back in again -- it is a magnitism thing I have been told

Frankly, I have a hard time believing that there is some magic voodoo in the way the factory installs the armature (other than being careful to prevent metal shavings from sticking to the magnets or making sure the armature is balanced). If someone can provide an actual explanation as to why removing the motor can can reduce power by the 10%-20% that has been stated on these boards, I would gladly admit that I am wrong, but I haven't seen one yet.

[Ellery]

Well Dr. Joe's point about the magnetism is one thing but for working on DC motor design for a bunch of years in my automotives years the removal of the can will impact the pressure placed on the armature by the thrust bearing , especially with the old seat and windowlift motors. These motors are dynotested and torque adjusted to spec on the line and once the motor is disassembled they will not return to the adjusted performance.

As far as the CIM motors go they may have a similar setup. It's a brushed motor with an armature that magnetized post assembly so once it is pulled out it may slightly affect the field by going against the permanent magnet fields. As always motor performance repeatability is always an issue once it is dismantled.

Just my 2 cents, It's been a while....

Ellery

[ColleenShaver]

I'm going to be that person who revives an old thread! It seems so rare in FIRST with changing people, changing kit parts, etc, that we really get to look at the long-term results of our designs.

In 2005, FRC190 utilized a mecanum chassis for the first time on the team. We had great concerns about the CIMs overheating in this style drive (the CIMs were new to the FIRST world back then).

To combat this, we modified the casing of the motors, allowed by the rules that year, with a large hole on one side and three smaller holes on the opposite side. A fan was mounted on top and the outer casing was turned down to remove the paint on the outside. This entire process was done solely to improve the cooling of the motors.

It caused a bit of a ruckus when it was learned that we did this, with some of the folks who post on here very concerned that we were at risk for some dangerous outcomes. You can see this closed thread for the details: http://www.chiefdelphi.com/forums/sh...ad.php?t=33313. On a side note, we DID NOT ask that Q&A, as the rules clearly stated casing modification was allowed so there was no reason to. However, another team who saw our robot asked because they didn't think it was supposed to be allowed and they misunderstood why we had done it.

Well, I'm happy to report 10 years later our 2k5 chassis still runs as happy as ever, with the same exact modified CIMs we competed with back then. The attached picture was taken earlier this season as the kids wired it up with the RoboRIO for program testing and driver practice use.

The fans have long failed, rollers have jammed and been replaced, and the encoders rarely work, but the motors have never been replaced. This chassis is used almost every year for some purpose, very commonly as an aggressively-driven defensive opponent in our driver practices. It's seen hundreds of hours of driving time more than your typical FIRST robot.

It remains to be seen if there would have been a cooling issue WITHOUT the modification, but the modification certainly never saw the catastrophic (or any) failures that were predicted.