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Electronic mechanical isolation


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James2



Joined: 07 May 2015
Posts: 115
Location: South Australia


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Electronic mechanical isolation

Was wondering if I could use a key lock out on a feather weight that locks out the power and weapon though a relay/electronic isolator paired with a remote isolator.
So the bot can only be powered once both key and remote are active at the same time.

Or dose it have to be a mechanical brake like a plug.

Post Sat Oct 31, 2015 5:17 pm 
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Nick
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Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


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You really have to have something mechanical - either a switch like most Aussie and US builders use, or a removable link, like the UK guys use. The simpler it is, the less chance of mistakes and failures!
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Post Sat Oct 31, 2015 5:59 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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Yes it needs to be mechanical. Any form of electrical system can fail even if its isolated.

The simpler the better.

Steve
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Post Sat Oct 31, 2015 7:27 pm 
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Valen
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Joined: 07 Jul 2004
Posts: 4436
Location: Sydney


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Relays and even mechanical switches will often weld,
In plan-B we had microswitches and a bolt we slid through a hole to deactivate the bot.

We found out the hard way that when pulling the bolt out the first microswitch would weld with the inrush current for the IBC then when we put the bolt back in the robot wouldn't turn off.

Not Great.

We got around it by putting a precharge resistor on one of the switches, but things like the bolt switches and removable links we use now are so much more reliable and positive that doing anything else feels like a serious step back.
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Post Sat Oct 31, 2015 11:06 pm 
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James2



Joined: 07 May 2015
Posts: 115
Location: South Australia


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Cheers great pointers that i didnt think of. I will have a mechanical brake in the cct.
Is relays welding such a common think on bots?
As using a few to control the pick axe motion. There rated well above the current/voltage usage. Due to the type of load I want to use mechanical ones over solid state ones.

Post Sun Nov 01, 2015 7:37 am 
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Nick
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Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


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Relays generally suck - I have destroyed quite a few over the years! You don't have to worry about the voltage rating on the contacts, its the current that kills them. Car relays are the worst, they often failed after just a couple of activations. Larger relays can also break from shock damage as the cases are made from quite brittle plastic, this also goes for solid state relays sold by Jaycar.

I had fair success with this relay:



http://www.robotcombat.com/products/0-SL1132.html

The metal base was pretty useless, wrapping it in foam will make it much more reliable. If you can find something similar to that, it should last.

The most reliable way to switch a motor is an ESC; depending on what you need to do, I would look at a TZ85a.
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Post Sun Nov 01, 2015 9:17 am 
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maddox



Joined: 21 Dec 2006
Posts: 786
Location: Belgium


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For mechanical relays that can handle the currents we regulary put trough the setups, I would suggest Albright .

Main disadvantage. Size. Pricetag and weight ain't funny either.

For "safety", the FRA rule that mandates a removable link as the minimum is enough for me.
EC'5 or XT90's can handle the job in our machines and can double op as fuze.

If a remote emergercy kill is wished for, a cheap trow away car relay that shorts the main power and blows the fuse -and relay-, is a simple and cheap way to have a 1 shot setup to do that.

Post Sun Nov 01, 2015 9:51 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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That's an interesting site! Looking at the spares section, the actual contact bars are just like the ones in the Whyachi switches - I wonder how hard it would be to use the contacts and build our own switches at a much lower price?
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Post Sun Nov 01, 2015 9:58 am 
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James2



Joined: 07 May 2015
Posts: 115
Location: South Australia


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Cheers, I will check those sites out.

Post Tue Nov 03, 2015 6:16 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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In case you haven't already seen it, this is the 'gold standard' of power switches:

http://www.teamwhyachi.com/MS1.htm



I could sell you a used MS05 from Decimator for $20 plus postage.
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Post Tue Nov 03, 2015 11:29 am 
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