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Unread 06-11-2007, 07:51
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Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
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Re: RAIV (Redundant Array of Independent Victors)

Quote:
Originally Posted by EricVanWyk View Post
I am reasonably certain that the Spikes do use "actual" relays. Can someone verify / deny this for us?

In any case, I do agree that the Spike would make a poor choice of mux for this type of task. I think that the battery terminals also power the logic inside, which basically eliminates this possibility.

Another solution would be to simply wire the Vics in parallel, but control them independently. Keep the backup in high impedance (127), and control the other one. If the primary busts, put it at 127 and control the backup.

Again, none of this is competition legal, but I think it is a very good exercise to think through.
The Spikes do use relays in an "H" bridge connection with an addition that allows certain output states that the Victors do not allow. The power input does power the internal logic as well as the relay inputs.

Remember that the Victors use power MOSFETs that have protection diodes built into their design. Trying to drive one into the open output of another may have catastrophic results for both devices.

A simple method for securing the PWM cables for both the Victor and Spike is to make a small bend in the cable and bring it right down to the mounting surface next to the device. Then use a tywrap to secure it in place. The PWM cannot be pulled out without cutting the tywrap. We use punched aluminum for our mounting panels which makes tieing things down very easy and lightweight.

Please remember, that we as mentors sometimes are considering things beyond your individual ideas when we respond. It is never our intention to stifle ideas. In this particular case, your desire for backup is sound, there is just no way to justify this idea under the current rules, the additional weight and space for components and complexity of the design. All of us have had heartbreaking failures due to simple problems. We lost a Championship match once because a pushon crimp connector on the fuse panel popped off. In another match a wire pulled out of a crimp on connector due to an improper crimp. To correct these problems, we now secure all wiring, and solder all connectors (using heatshrink for insulation), check all screws after every match to be sure they are tight and run function tests to make sure everything is working before we send it out. In spite of all of this, Murphy still strikes. In a division title match at Championships, we thought we had forgotten to put a charged battery on the robot only to find out that damage from an earlier collision had caused a dead short in one of our motors. Stuff happens!
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.