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on/off Switches and wiring


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rjw



Joined: 04 Jul 2010
Posts: 110
Location: Miami, Fl. USA


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on/off Switches and wiring

Do you guys wire the positive or negative thru your on/off switch?

Post Sun Jun 09, 2013 10:26 pm 
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marto
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Joined: 08 Jul 2004
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Location: Brisbane, QLD


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Positive. But really doesn't matter unless you have used chassis as ground.

Steve
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Post Sun Jun 09, 2013 10:50 pm 
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rjw



Joined: 04 Jul 2010
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Location: Miami, Fl. USA


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Same here , but have been experiencing some wierd stuff lately with fingertech switches in our steel 3 pounders.

Once in a while, when inserting an allen wrench thru a steel cover and turning the switch screw, I get arcing between the allen and the cover??

The switch screw is live once contact is made , which is not the greatest thing

I'm going to run the ground side thru the switch, which should solve the problem.

ps: no shorts in the wiring on anyhthing and this makes 2 bots that do this, but it doesn't always happen. I am wondering if this is happening thru an esc or motor?

Any thoughts

Post Mon Jun 10, 2013 12:10 am 
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dyrodium
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Hmmm definite short to frame there. Easiest way to track it down would be to have at it with a multimeter (battery removed!) Shocked
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Post Mon Jun 10, 2013 12:16 am 
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marto
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Brushless motors shouldn't be the cuprit. No reason why ESC would be attached to frame. I would have to say stray wire or maybe those 1000rpm motors.

Steve
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Post Mon Jun 10, 2013 12:20 am 
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rjw



Joined: 04 Jul 2010
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Location: Miami, Fl. USA


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tried that with no luck..it's wierd, because it doesn;t always happen, plus it looks like a sparkler. I've dealt with shorts before, you get true arcing and contact points look burnet, etc. this is like a mini sparkler / light show...kindof strange, but a bit scary. Perhaps the esc heat shrink is thin enough that any ground points on the esc are trying to go to ground. I meticulously checkedthat everything was ok, no tears nothing exposed or touching ground, and yet it still happens once in a while

Bots run fine once activated??

Using 65c lipos, if there was a short, I'd know quick enough, I think!? Embarassed

Post Mon Jun 10, 2013 12:22 am 
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MikeNCR



Joined: 05 Jan 2012
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Location: Norcross, GA USA


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I just put heat shrink on all but the tip of the wrench I use for the switch so it avoids the arcing issue entirely.

Post Mon Jun 10, 2013 12:35 am 
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rjw



Joined: 04 Jul 2010
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Location: Miami, Fl. USA


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quote:
Originally posted by MikeNCR:
I just put heat shrink on all but the tip of the wrench I use for the switch so it avoids the arcing issue entirely.


gotcha...I used to do that way back when, but....

thanks again Mike!! Smile and Steve Razz

Post Mon Jun 10, 2013 1:18 am 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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I wouldn't put too much faith in insulating the alen key with heatshrink; I did that (just to ID the right yey in the toolbox) and when I had a short to the frame, I found the heatshrink had been cut by the sharp edges of the cover and STILL shorted!

Try using 2 or three layers of heatshrink to be sure, but this isn't finding the underlying problem. With a 65C Lipo waiting to explode, you really should find the short to the frame before the positive side also shorts out. If the problem is intermittent, I would be looking for small cuts in the negative side wiring. Also look for arcing marks on the frame, particularly on any sharp edges.

It might be a smart move to cover suspect parts of the frame with insulation. Duct tape is cheap 'easy, but my favourite is adhesive-backed UMHW film, like # 1441T51 from McMaster. It is about twice the thickness of tape and is still fairly flexible. The main attraction is that it is highly abrasion and puncture proof.

Post Mon Jun 10, 2013 10:38 am 
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Daniel
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Joined: 30 Aug 2005
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I saw this at RoboGames. A middleweight team went to power up a robot and the chassis arc'd with the allen key. They were immediately disqualifed and not given any time to fix it. I had a faulty power switch and was given a postponment to fix it, but a live chassis was considered a disqualifying offence. I suggest you find the fault rather then by-passing it with heat shrink on the allen key. Short cuts will end up biting you.

Post Mon Jun 10, 2013 10:31 pm 
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Nick
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Or exploding you! Laughing

Post Mon Jun 10, 2013 10:40 pm 
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rjw



Joined: 04 Jul 2010
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Location: Miami, Fl. USA


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I'm working on a few things. When the smoke clears , I'll post the resulst of my tests, but so far there are NO shorts in any of 3 bots tested and all three exibit similar symptoms....once again. not always, but often enough that I need to get it solved.

Post Thu Jun 13, 2013 11:15 am 
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