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Old 01-07-2020, 02:39 PM
travbowls travbowls is offline
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Default Electric tracked mini Tank project

Hey everyone, I'm a newb here, but not a newb to building stuff. I'll jump straight into my questions, and would SO thankful for any help. I built a 1/4 scale (a little bigger in some dimensions) Sherman Tank for the kiddo's.
I'm currently trying to decide on batteries. I'd love to use golf cart 6v's, but don't have $1000 to throw at this. I'd prefer to start with say, a $200 option. I'm considering:
-(2) china made Li-Ion 48v 12ah, for about $100 each.
-(4 or 8) PowerWheels style SLA batteries, say like 12v 18AH each.
- 4 normal Deep cycle batteries, at like $70 each if I can find a deal.

Usually people ask questions with not enough info, so excuse me if this is too much. History of the project:

It started with a couple 24v motors from a mobility scooter, with 1 speed controller that I spliced between to add my own reverse, and separate controls for each side of the tank using 24v HVAC relays. This setup was pretty unreliable (popping breaker and weird controls) and underpowered. I was going to go with a gas engine, but then you need a transmission, hard to start for kids, exhaust/fuel fumes in an enclosed hull, etc etc.

I now have (2) 48v 1000w motors (MY1020), 1 for each side. And each has it's own speed controller with reverse, and throttle pedal. I'm making levers which actuate the pedal either way (F or R), but pushes a little button when going in reverse to tell the controller that side is in reverse. There is a 3/4" jackshaft for each side with the following gearing:
Motor: 11t to 44t jackshaft IN.
Jackshaft OUT 18 tooth, to 38 tooth on the track drive sprockets. For about 8:1 reduction. The track drive sprockets are 5.5", but effectively 9" OD with the track wrapped around them.

My goal with this tank is to make it through a parade route, and play around in the snow, gravel pit, or sand. Speed in NOT really a factor. 2-7 mph is fine.




I will add some more pics when I can.
Thanks for having me

Last edited by travbowls; 01-07-2020 at 02:48 PM. Reason: Added pics
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  #2  
Old 01-07-2020, 08:35 PM
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Wow! You win at Dadding! Post some video! And hook up a big nerf gun in for the cannon!

And what did those tracks come off of? You need to post more pics of that build for us to drool over!

For batteries the 12v 22ah should be enough to get you a solid 20min of ride time. If you need more you can add 12v 12ah or more 18-22ah batteries. Or bite the bullet and go with Nissan leaf cells 48v 60ah pack would probably run you around 300$. Another option would be a few 56v 4-7.5ah cordless tool battery packs. that you could swap in and out as needed or run in parallel. Clearance section at homedepot and lowes is good for picking those up cheap.
https://www.ebay.com/itm/4PK-NEW-12V...YAAOSw-6BcpmDr
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Old 01-07-2020, 09:39 PM
travbowls travbowls is offline
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Cool, thanks. Those 22ah ones seem like the way to go I'd say. I could start with 4, then add 4 more as I get closer to parade time. They are what, 13lbs each, so only 100 lbs for 8, not bad.

I have some video, but like I say, it was painfully slow, haha. Here's a little montage of the build, the tracks are made of conveyor belt, 3/4" Uhmw, and lots of time on the table saw, haha.
https://youtu.be/KLk46Z1maZA

I'm still curious why no one seems to use those 48v li-ion batteries. Is there something with the power delivery or initial amps/load or something? Seems like mobility Scooters, go karts, etc all still use the SLA's.

Thanks again for any help. I'm glad there seems to be some serious experts on here with the know-how of these motors and controllers, etc.
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Old 01-07-2020, 10:41 PM
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Welcome to the forum!!! Awesome build. I have no experience with electrics so i cannot help you on that side. I will just be drooling over the rest of the build though
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Old 01-08-2020, 06:51 AM
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Wow! Very Kool!
Maybe check out the !Arriba! kart

http://www.diygokarts.com/vb/showthread.php?t=37852

It runs on (2) 48V 1,000W motors (very powerful little motors)
& (4) Mighty Max 12V 15AH SLA batteries

I usually get ~20 -30 min of run time
& it takes ~4-5 hrs. to charge 'em back up

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Old 01-09-2020, 04:15 PM
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Thanks again for the input. I went ahead and ordered (4) 12v 22ah Mighty Max batteries. I figure I can always add 4 more before the next parade if I need more run time.
I also went over to my neighbors house and we made a new, much prettier motor mounts plate on his plasma table, with slotted holes for chain tightness adjustment.
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Old 01-15-2020, 12:41 PM
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I'm about to tackle the wiring, batteries arrive any day. One question I have, is about the fuses.
The speed controller documentation said Maximum current 40 Amps. I have seen some discussion on 30a vs 40a fuses, I got both, and assume I'd start with the 30's.

But the main question I have, is, when using a single battery pack, to power both speed controllers and motors, I assume it's better to have a separate fuse before each controller? Or does it not matter? Also, are fuses needed anywhere else?

Thanks again
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Old 01-15-2020, 12:53 PM
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Lucky your neighbor must be awesome!
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Old 01-15-2020, 07:54 PM
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Well two fuses one per controller.
With a decently made controller the 30A should be okay for a kid's toy vehicle.
In case the controller isn't ramping on startup however a higher value and/or slow blow fuse is recommended. maybe even something like 45A may be needed.

Reason: if everything is cold and tight and you throttle up,
there might be a peak current rushing through
the instant the MosFets are switching.
that peak can exceed the maximum controller rating.

A 40A slow blow fuse should still be okay (it might be able to deal with the short peak)
but it's hard to tell for sure, so in case it's not don't worry too much,
just get a slightly higher value and try again.. only if you exceed say 60A per controller I would search for shorts and such.

Thinking about it, a resettable fusebox might be your best bet perhaps
as it doubles as a safety disconnect for storage/charging and so on.

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