Team Update #11

[Akash Rastogi]

Originally Posted by ratdude747

4.4.1 Robot Wireless Control
 Robots may be operated via wireless control only on the competition fields and the
practice field with the FIRST supplied radio; and
 Teams are not allowed to set up their own 802.11a/b/g/n (2.4GHz or 5GHz) wireless
communication (access points or ad-hoc networks) in the venue

sounds like scouting may be more of a challenge this year...

This has been part of the rules since 09.....

[thefro526]

Originally Posted by AllenGregoryIV

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

My understanding is that the ridge will be the height of the 3/16" HPDE Plus the Carpet that covers it. I'd imagine that it would be no more than 3/8" but I cannot be sure. The description is a bit confusing, a drawing would be nice.

[IndySam]

Basically they removed the 1/4" because there is no real way to say exactly how big the bump will be.

A hard number like that will only cause headaches with teams complaining about it being to high when it's not exactly 1/4"

So they are saying "this is how it's constructed plan accordingly YMMV."

[Teched3]

Originally Posted by EricH

http://usfirst.org/uploadedFiles/Rob..._Update_11.pdf

Updated manual to follow tomorrow. Burned out Tetrix motor inductors may be replaced, and parts may be repaired (keep the performance the same, though)--though teams are encouraged to use caution when doing to, and assume voided warranties.

It seems the GDC has come up short by allowing us to repair burned out components on the Tetrix motors. How many times can you bend those retaining tabs before they break off? How will they be able to determine if the replacement inductor/capacitor was the exact replacement? What they should've included, IMO, was to allow us to put minifuses on the motor lead(s) to protect the motors. It is just poor safety and engineering practice not to have those motors properly protected. Sort of closing the barn door after the horse has gotten out. Anyone else out there agree?

[Chris is me]

Originally Posted by IndySam

So they are saying "this is how it's constructed plan accordingly YMMV."

What good will that do a week before ship?

[PaW]

Originally Posted by ratdude747
4.4.1 Robot Wireless Control
 Robots may be operated via wireless control only on the competition fields and the
practice field with the FIRST supplied radio; and
 Teams are not allowed to set up their own 802.11a/b/g/n (2.4GHz or 5GHz) wireless
communication (access points or ad-hoc networks) in the venue

sounds like scouting may be more of a challenge this year...

Originally Posted by Akash Rastogi

This has been part of the rules since 09.....

This is a good opportunity to remind students, mentors, parents, guests, etc. to disable the "hotspot" capability (and battery sucking feature) of the current generation of smartphones.

Each venue is different of course, so please make sure to check with your local director or coordinator. Some venues may have 'free wifi' in their concourse areas, and your scouting members might be able to set-up in those areas.

[Racer26]

The wifi (no team-setup 802.11a/b/g/n networks allowed) rule has always perplexed me. It actually has existed for as long as I can remember in FRC (yes, it PREDATES the cRIO and robot control systems running on 802.11n.)

The old IFI controls ran on 900MHz radio modems (they run an RS-422 Serial link over a radio connection).

The current cRIO+wifi controls run using 802.11n in the 5GHz band, everywhere except Israel, where 5GHz is a restricted military frequency, so they use 802.11n@2.4GHz.

The rule has always been in place with the intent of preventing robot interference, and it USED to outlaw ALL wireless communication devices in ANY band, except for cell phones IIRC. (this meant teams couldn't use walkie talkies or similar devices)

I've always found it silly for several reasons.

Cell phones regularly make use of the 900MHz frequency band, especially historically during the era of the IFI controls. If interference was such a problem, the literally hundreds of cell phones at an FRC event should have caused some robot weirdness. None occured, to my knowledge. Fast forward to today, and smartphones are now equipped with Wifi abilities, simultaneously operating in several frequency bands. You could never outlaw bringing your cellphone to an FRC event. It would be impossible to police.

Event venues, and indeed, even FRC events themselves, frequently have Wifi running at, or within range of FRC events. Additionally, the 2.4GHz, and 5GHz bands are unlicensed bands, usable by anyone for anything, anywhere in North America. Many FRC events have residential, commercial, industrial, or institutional lands within range. Interference in this band comes from all over the place, whether or not teams are wilfully adding to it or not.

The 802.11 standard (in all flavors) has proven itself to be fairly resilient to interference, otherwise you and all your neighbors couldn't run your wifi routers in such close proximity to one another without causing problems. Furthermore, since FRC is using the comparitively unused 802.11n @ 5GHz, any interference in the 2.4GHz or 900MHz bands would cause no problems at all.

If interference were a true problem for FRC bots (its not), FRC could apply to the FCC and CRTC to use the licensed 3GHz band. I know of at least one company that makes 802.11 compliant devices using that band. This solution would surely eliminate any interference concerns, however, it would potentially be problematic in that each team might have to apply for a license, unless FIRST could convince both CRTC and FCC to grant the program a blanket license.

[Bill_B]

Originally Posted by Teched3

It seems the GDC has come up short by allowing us to repair burned out components on the Tetrix motors. How many times can you bend those retaining tabs before they break off? How will they be able to determine if the replacement inductor/capacitor was the exact replacement? What they should've included, IMO, was to allow us to put minifuses on the motor lead(s) to protect the motors. It is just poor safety and engineering practice not to have those motors properly protected. Sort of closing the barn door after the horse has gotten out. Anyone else out there agree?

It is quite possible, likely even, that GDC had no idea how these motors would react to the devil-may-care "design" work done by our enthusiastic high-schoolers. Can you give us more details about the minifuses? I would put them into my test machinery regardless of competition legality, then remove them for competition.

As far as I can tell the biggest oversight was the failure to include motor leads at all in the first choice parts kit. They ran down the list of needed motor stuff to add to the resource kit but fell short of even the standard connection method. That connector is at least designed for the machine. No visible strain relief in it and no way to secure it to the motor either. I get the idea that it's an afterthought from Tetrix.

[ratdude747]

Originally Posted by 1075guy

The wifi (no team-setup 802.11a/b/g/n networks allowed) rule has always perplexed me. It actually has existed for as long as I can remember in FRC (yes, it PREDATES the cRIO and robot control systems running on 802.11n.)

The old IFI controls ran on 900MHz radio modems (they run an RS-422 Serial link over a radio connection).

The current cRIO+wifi controls run using 802.11n in the 5GHz band, everywhere except Israel, where 5GHz is a restricted military frequency, so they use 802.11n@2.4GHz.

The rule has always been in place with the intent of preventing robot interference, and it USED to outlaw ALL wireless communication devices in ANY band, except for cell phones IIRC. (this meant teams couldn't use walkie talkies or similar devices)

I've always found it silly for several reasons.

Cell phones regularly make use of the 900MHz frequency band, especially historically during the era of the IFI controls. If interference was such a problem, the literally hundreds of cell phones at an FRC event should have caused some robot weirdness. None occured, to my knowledge. Fast forward to today, and smartphones are now equipped with Wifi abilities, simultaneously operating in several frequency bands. You could never outlaw bringing your cellphone to an FRC event. It would be impossible to police.

Event venues, and indeed, even FRC events themselves, frequently have Wifi running at, or within range of FRC events. Additionally, the 2.4GHz, and 5GHz bands are unlicensed bands, usable by anyone for anything, anywhere in North America. Many FRC events have residential, commercial, industrial, or institutional lands within range. Interference in this band comes from all over the place, whether or not teams are wilfully adding to it or not.

The 802.11 standard (in all flavors) has proven itself to be fairly resilient to interference, otherwise you and all your neighbors couldn't run your wifi routers in such close proximity to one another without causing problems. Furthermore, since FRC is using the comparitively unused 802.11n @ 5GHz, any interference in the 2.4GHz or 900MHz bands would cause no problems at all.

If interference were a true problem for FRC bots (its not), FRC could apply to the FCC and CRTC to use the licensed 3GHz band. I know of at least one company that makes 802.11 compliant devices using that band. This solution would surely eliminate any interference concerns, however, it would potentially be problematic in that each team might have to apply for a license, unless FIRST could convince both CRTC and FCC to grant the program a blanket license.

thats funny, i can always seem to remember teams having wireless networks set up for scouting... if the rule has existed that long, has it really been this poorly enforced?

[Teched3]

Originally Posted by Chris is me

What good will that do a week before ship?

You can withhold the minibot and insert fuses in the feed lines from the motor at your liesure. It would take a few dollars for the parts, and about 10 minutes. Hopefully you're prototyping using fuses. Certainly a lot less time and expense than taking a motor apart and replacing an inductor, or the complete motor assembly.

[Teched3]

Originally Posted by Bill_B

It is quite possible, likely even, that GDC had no idea how these motors would react to the devil-may-care "design" work done by our enthusiastic high-schoolers. Can you give us more details about the minifuses? I would put them into my test machinery regardless of competition legality, then remove them for competition.

As far as I can tell the biggest oversight was the failure to include motor leads at all in the first choice parts kit. They ran down the list of needed motor stuff to add to the resource kit but fell short of even the standard connection method. That connector is at least designed for the machine. No visible strain relief in it and no way to secure it to the motor either. I get the idea that it's an afterthought from Tetrix.

You can pick up minifuse holders and fuses at any car stereo shop or auto parts store. I would suggest you start out with 2 - 2.5 amp fuses, and have spares on hand. They originally had the less expensive motor leads listed, then added the thermal protection leads (at about 4x's the price), which do not react fast enough to protect the motors. Remember, these components are used in robots that run across the floor. That is a whole lot different than using them to climb a 10 ft. vertical pole. In addition, these components are"new" to even experienced FTC teams for the same reason.

[Justin Montois]

Originally Posted by martin417

After talking with an EE, I have been informed that there COULD be significant gains by replacing the inductor with a wire. Possibly as much as a 10% power boost. has anyone tried this? An easy test for this is a resistance check across the motor windings. The motor winding resistance is normally quite low, so a quick check could show that someone has "mistakenly" replaced the inductor with a non-complying part.

We found around 20ohms of resistant across the windings with a stock motor and 6 ohms with just a wire in place of the inductor. Pretty big difference.

Does anyone know if the inductor I listed earlier in this thread an identical part?

[Racer26]

Originally Posted by ratdude747

thats funny, i can always seem to remember teams having wireless networks set up for scouting... if the rule has existed that long, has it really been this poorly enforced?

Prior to 2009 when the cRIO+wifi became the method of doing things, and there was 6 Wifi networks required to just run a match, it was just that poorly enforced.

2009-present, the FTAs have had spectrum analyzers and stuff hooked up, and can tell what Wifi is going on in the area. If teams set up their robot on wifi in the pits, the FTA will know about it.

[Al Skierkiewicz]

Guys,
Although the Bourns page is similar it is not nearly the identical part. When I first started research on this a few weeks ago, I found an identical sized inductor with the same conformal package. I believe they were more like 900ma max DC current. The series resistance is much lower than the Bourns above. AT 900 ma used with a motor that stalls at 7.5 amps, you can see why the motors constantly burn open.

BTW, I started the discussion to allow opening Tetrix motors to replace the inductor. My recommendation was based on the purchase cost factor of replacing a motor that had failed simply because an under rated part had failed. I had hoped that teams could cut their losses by replacing the inductor. FIRST and the GDC was overly generous by allowing teams to open and repair other items besides the Tetrix motor and delineating "repairs" from the "modification" rules.

[Bill_B]

Originally Posted by 340x4xLife

We found around 20ohms of resistant across the windings with a stock motor and 6 ohms with just a wire in place of the inductor. Pretty big difference.

Does anyone know if the inductor I listed earlier in this thread an identical part?

That's a big help in telling whether a motor is repairable. My armature coils measured much less than 20 ohms. That is further support for my presumption that there is invisible damage to my coils internally.

I'm confused about your 6 ohm measure though. Why would shorting the inductor cause less than the coil winding resistance?

So, my advice now about trying to repair a motor is to measure your coils first, across all three pairs of commutator contacts. If you find a coil pair that is significantly less than 20 (or 6?) ohms, don't bother trying to replace the inductor. Even if you were to get an operating motor going, its work and power characteristics will be different than a stock motor. That would make the repaired motor questionable to use for prototyping. It might still be useful as an arm mover on an FTC robot though.