Capacitors on speed controllers

FIRST General Forum
1

Posted by colleen, Student on team #126, Gael Force, from Clinton High School and Nypro.

Posted on 3/21/99 6:14 PM MST

In our first elimination match, our alliance’s (team #19 Bell Atlantic/GreenwichHS) robot went dead. when checking out the situation, they said it was because they didn’t have capacitors on our speed controllers (neither did our robot), but let the match be re-run because FIRST never specified that point at the beginning and was trying throughout the competition to get teams to put them on.

i was just wondering if anyone new the real ruling on that (although i’m sure/hope there will an update regarding it)? at any of the other regionals were teams advised to put them on the InnovationFIRST SC, or was this only at the UTC Regional?

2

Posted by Jerry Eckert, Engineer on team #140 from Tyngsboro, MA High School and New England Prototype/Brooks Automation.

Posted on 3/21/99 6:43 PM MST

In Reply to: Capacitors on speed controllers posted by colleen on 3/21/99 6:14 PM MST:

:
: In our first elimination match, our alliance’s (team #19 Bell Atlantic/GreenwichHS) robot went dead. when checking out the situation, they said it was because they didn’t have capacitors on our speed controllers (neither did our robot), but let the match be re-run because FIRST never specified that point at the beginning and was trying throughout the competition to get teams to put them on.

: i was just wondering if anyone new the real ruling on that (although i’m sure/hope there will an update regarding it)? at any of the other regionals were teams advised to put them on the InnovationFIRST SC, or was this only at the UTC Regional?

I was just about to post a note on this same topic…

As many of you are aware, FIRST has been advising not to put the bypass capacitors on the
motors this year to eliminate short circuits caused by the capacitor leads. At the Hartford
check-in we were strongly advised to place the capacitors across the output terminals of all
speed controllers - not just those controlling the drill motors. Apparently there have been
a number of problems they believe to have been caused by noise interfering with the speed
controllers and even the receiver.

Another note – make sure you use the attenuator on the receiver antenna.

Even with the capacitors we had severe problems with data corruption errors which left the
robot essentially dead. These problems occurred only when operating from one position on
one field: it worked fine in the pits and from the other three positions. FIRST claimed
this was due to the attenuator not being used on the receiver antenna. I can’t verify
this was actually the problem as we didn’t have another match in that position after
correcting the problem, but I wanted to give everyone a heads up so they can make sure
they don’t run into the same situation.

- Jerry
3

Posted by Andy Grady, Coach on team #42, P.A.R.T.S, from Alvirne High School and Daniel Webster College.

Posted on 3/22/99 9:39 PM MST

In Reply to: Re: Capacitors on speed controllers and antenna attenuators posted by Jerry Eckert on 3/21/99 6:43 PM MST:

My team also ran into a problem with the noise on the reciever which ended up in our having to make a rematch in one round. We were told by FIRST that they changed their mind about capacitors during the UTC New England Regional. So if you want to avoid future problems, get those capacitors on your speed controlers.
Good luck to all,
Andy Grady, DWC/Alvirne

4

Posted by Frank of team #97, Psychedelics, from CRLS sponsored by MIT.

Posted on 3/24/99 9:48 AM MST

In Reply to: Re: Capacitors on speed controllers and antenna attenuators posted by Jerry Eckert on 3/21/99 6:43 PM MST:

That one station that you were having problems
wouldn’t be red A, would it? For the last three
years my team has had some problem or another with
data errors in the red position. It continued again
in NJ this year in the Red “A” position. FIRST
swears that there is nothing wrong with it, but it
seems to be too much of a coincidence. They reuse
r-nets and the driver’s stations from year to year,
so if there is a problem, it could continue from
year to year. Have any other teams experienced this?

Good luck to all in Detroit!!

Frank
Team 97 - MIT/CRLS '99
Team 111 - WildStang '96-98

5

Posted by Jerry Eckert, Engineer on team #140 from Tyngsboro, MA High School and New England Prototype/Brooks Automation.

Posted on 3/24/99 10:24 AM MST

In Reply to: Data problems on Red field posted by Frank on 3/24/99 9:48 AM MST:

: That one station that you were having problems
: wouldn’t be red A, would it? For the last three
: years my team has had some problem or another with
: data errors in the red position. It continued again
: in NJ this year in the Red “A” position. FIRST
: swears that there is nothing wrong with it, but it
: seems to be too much of a coincidence. They reuse
: r-nets and the driver’s stations from year to year,
: so if there is a problem, it could continue from
: year to year. Have any other teams experienced this?

Looking at the stage from the seating area, it was the left
side of the left field. I think they were calling that
field B; I don’t recall which color it was. We were in Hartford,
so it probably doesn’t matter since I doubt they assign specific
Rnets to specific positions from regional to regional.

- Jerry
6

Posted by colleen, Student on team #126, Gael Force, from Clinton High School and Nypro.

Posted on 3/24/99 3:22 PM MST

In Reply to: Re: Data problems on Red field posted by Jerry Eckert on 3/24/99 10:24 AM MST:

we were in hartford too, and the problems for our alliance occurred on the blue side of the A field, and our problems occurred on the red side of both fields… so i don’t know if that was an issue…

7

Posted by Thomas A. Frank, Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.

Posted on 3/26/99 10:54 AM MST

In Reply to: Re: Capacitors on speed controllers and antenna attenuators posted by Jerry Eckert on 3/21/99 6:43 PM MST:

: Another note – make sure you use the attenuator on the receiver antenna.

: Even with the capacitors we had severe problems with data corruption errors which left the
: robot essentially dead. These problems occurred only when operating from one position on
: one field: it worked fine in the pits and from the other three positions. FIRST claimed
: this was due to the attenuator not being used on the receiver antenna. I can’t verify
: this was actually the problem as we didn’t have another match in that position after
: correcting the problem, but I wanted to give everyone a heads up so they can make sure
: they don’t run into the same situation.

The attenuator may not be the solution to the problem. We went through this last year…first
we used the 10 dB attenuator, no luck. Then we went to a 20 dB attenuator, still no luck. Then
I got that feeling like maybe we had done something ‘weird’, so I ran a signal strength meter
up and down the structure of our machine; what I found was that we had placed the antenna at an RF “null”
on the robot. Which is to say, with a transmitter operating in the RNet freq range nearby, the signal
strength on the robot at the antenna was virtually zero. I moved the antenna several inches, and the
entire problem disappeared. Several other teams were experiencing the same problem in NH, and after
they moved their antennae the problem seems to have sorted itself out.

In our case, I suspect we accidentally made a waveguide (the RNet’s work at about 460 MHz, lambda = 26"
at this freq, which was very close to the dimensions of our structure); or perhaps the shape yielded
destructive interference at our antenna location.

Regardless of the cause, moving the antenna solved the problem…we did make it to the finals in FL…while
we really had problems in NH…

So I would strongly suggest that you also try moving the antenna. It’s simple, free, and it might solve the
problem for you.

I’d also check the cable from the RNet to the receiver box. FIRST has experienced some QC problems in this area
over the years.

Tom Frank

8

Posted by Tom S., Student on team #177, The Bobcats, from South Windsor High School and International Fuel Cells & ONSI.

Posted on 3/26/99 5:05 PM MST

In Reply to: Capacitors on speed controllers posted by colleen on 3/21/99 6:14 PM MST:

:
: In our first elimination match, our alliance’s (team #19 Bell Atlantic/GreenwichHS) robot went dead. when checking out the situation, they said it was because they didn’t have capacitors on our speed controllers (neither did our robot), but let the match be re-run because FIRST never specified that point at the beginning and was trying throughout the competition to get teams to put them on.

: i was just wondering if anyone new the real ruling on that (although i’m sure/hope there will an update regarding it)? at any of the other regionals were teams advised to put them on the InnovationFIRST SC, or was this only at the UTC Regional?

Grrr… we (Team #177 and #69) would have won that match =)
-Tom S.
Team 177

PS: Everyone please put them on so this doesn’t happen again =)