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Electrical systems


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Arkinto



Joined: 15 Oct 2014
Posts: 20
Location: Brisbane, Australia


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Electrical systems

Hi everyone, I'm well on my way building my robot and currently up to organising the electrical systems.
So my robot consists of 4 18V 60A (stall current) drive motors w/ gearbox and 2 weapon motors (same type) connected to botbitz esc's.

So now I'm trying to decide the appropriate batteries and connections.

I found A 5S 4000mAh 40C lipo for a fairly good price. The weapon motors I expect will likely reach stall a couple of times which is why I chose that battery. Does that sound alright?

For the 4 drive motors I'm still deciding on going for another of that 5S 4000mAh 40C lipo battery, since the wheels should never reach stall I figured this could be a good choice? Else perhaps doing 2 packs; something like 5S 4000mAh 30C each. If I can get away with the 1 battery pack for the drive motors, that would be great since it means less weight, but I'm not sure on whether that's something I should do.

The other concern I have is with the battery connectors, the batteries at any time could be required to pull current over the 60A rating of the XT-60 connectors and could pose an issue like melting? I'm obviously not that sure on how sturdy the XT-60 connectors or how long they will last before they fail in my system. But the main battery I think could have to provide 30A each motor = 120A, don't know whether that would bode well for the battery connector so should I change it to an XT150 connector
And last issue, my main weapon uses linear actuators (for a pincer weapon) I've made myself and I'm wanting to put limit switches on them so it doesn't bottom out hard when I'm controlling it. Since the motors are 18V 60A at stall I would need a limit switch rated for that current, which as far as I can see, may be a bit of an issue getting. So my next thought is an 18v 60A relay connected to a small limit switch which might be a better idea and next idea after that is using a mosfet/transistor to handle the high current switching which may not be a good idea. Alternatively I could also just be careful and not let it bottom out hard when controlling it.

Edit: Also the motors are RS-550 18v motors but I can't find the datasheet anywhere unforutunately. I may also need to do some mixing with my hobbyking 6ch controller but hobbyking doesn't have any in aus stock, I'm wondering if this cable is infact just a USB to TTL converter cable?

Thanks! Smile

Post Thu Apr 26, 2018 1:16 am 
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marto
Experienced Roboteer


Joined: 08 Jul 2004
Posts: 5459
Location: Brisbane, QLD


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The XT60s will be fine. If the melt think of them as a fuse as something has gone wrong.
If you are worried about the battery bump it over to an XT90 but the Tabs on the battery pack will melt off first.

There is lots of things to worry about but just stick to the XT60s and get it working then if it poses an issue upgrade them. But I will bet a bag of XT90s that the 60s will be perfectly fine in a sportsman.

Steve
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Steven Martin
Twisted Constructions
http://www.botbitz.com

Post Thu Apr 26, 2018 2:09 pm 
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Ondray



Joined: 06 Jul 2015
Posts: 139
Location: Newcastle


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Yeah my 4 motor drive bot would pull over 100A at peak, XT60's handle it fine. Just don't use low quality cables - I used 12G cable from supercheap and melted the wires before the connectors! 12G hobby grade stuff is fine.

Post Thu Apr 26, 2018 5:51 pm 
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marto
Experienced Roboteer


Joined: 08 Jul 2004
Posts: 5459
Location: Brisbane, QLD


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Dat sweet silicone wire.
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Steven Martin
Twisted Constructions
http://www.botbitz.com

Post Thu Apr 26, 2018 7:15 pm 
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Arkinto



Joined: 15 Oct 2014
Posts: 20
Location: Brisbane, Australia


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lol thanks for the tips guys, sounds like the XT60's should be good for me to use, I guess I'll stay with the 1 battery for 4 motors and do some load tests, chassis is pretty much done so I can test it all in the robot, if they go over the battery current rating I'd say it's probably a good idea switch to a different battery (or 2).
I always use cables from Jaycar which seem pretty good (albeit a little overpriced I assume)

Post Thu Apr 26, 2018 11:09 pm 
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timmeh
Experienced Roboteer


Joined: 20 Jul 2004
Posts: 2521
Location: Victoria


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Hey guys not sure if this is the right spot to ask about silicone wire but here it goes.

I am so used to auto wire and only new to silicone wire and trying to work out what sizes to use. any advice on amps and reliability in robot use would be appreciated.

Something bugging my OCD is i have a yep 150a weapon speed controller which has 12awg input wires i have seen the hobbyking 200a with the same. now it seems 12awg silicone wire is rated for 70amps?? according to one chart i have seen then again i have seen 12awg silicone rated 70 88 120 125amps on other charts lol

My 80a escs have 12awg input and i feel that is ok since them being drive esc's they wont be continuously drawing high current.

Would it be worth upgrading the wire to 10awg on the 150a esc, altho wondering if the tracks in the board are even thick enough to warrant the input wire upgrade.
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Tim Team Reaper.

Post Fri Mar 29, 2019 2:05 pm 
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