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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: 5458
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: 137
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: 5458
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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