#25 sprockets go down to 9 tooth, which is under 19mm - probably not from a pocket bike supplier though.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Yeah bud, give this a try, i think this is Shane's business? He used to be on the forum under Bytraper, maybe drop him a message

https://www.motiondynamics.com.au/25-motor-sprockets/


The pocket bike pinion sprockets go all the way down to 6 tooth and have an m8 thread on the end, but the 200-300w scooter motors have the same pitch chain too, those sprockets might be handy.

#25 is super common so most engineering shops should stock the bigger sizes worst case.
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

just be really careful with chains and alignment, they love to run off in robots
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Mechanical engineers build weapons, civil engineers build targets

What he said! If you can fit it in, a tensioning device will help keep the chains on.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Just mount wheel direct.to motor and skids maybe?
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Andrew Welch, Team Unconventional Robotics

4WD full body spinner, very cool. I say stick with 4WD, it will help it to be stable and drive in a more predictable fashion and when the weapon system fails you'll have some pushing power. Chain or timing belts would be my suggestion also
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<Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls

I like the robot you're building, it's quite impressive (that shell, wow).

Watching the video I was going to suggest utmost caution (I didn't post a testing video a while ago in which brick debris almost smacked me in the face) but then you found that one out for yourself.
I found the problem to be that a shell spinner is constantly firing its weapon in all directions so you really have not much control at all in terms of which directions it's safe to have people in.

Your robot looks to have good potential once you iron out some of the bugs; just try not to seriously injure yourself (or others) along the way
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http://au.youtube.com/user/crustydemonsully

The day I stop giving 100%, is the day I stop competing

looks awesome... hows the weight going?
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Miles Blow - Julie Pitts
www.mulesfilm.com.au
www.wombokforest.com.au

-Pickasso- Vivid Sportsman champion 2015

Thanks for the ideas guys I am in Melbourne atm but when I get home will be putting some ideas into action! And she is sitting at 12.36kg atm
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Creative Instigation - Build Something Awesome!

https://www.youtube.com/channel/UCTuWeJ4OrAcsmjKir9L4JNg

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Very nice work having a whole kg and that spinner.

I look forward to you sending parts of my robot to every corner of the arena
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Remember to trust me, I am an Engineer.

http://www.youtube.com/watch?v=rp8hvyjZWHs

i have fixed the traction issue!

6WD



(will still be belt driven to the outer wheels) I know the ratio is out but meh running out of time
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Creative Instigation - Build Something Awesome!

https://www.youtube.com/channel/UCTuWeJ4OrAcsmjKir9L4JNg

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Don't bother

Direct drive middles and use others as castors. Will still drive great
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Andrew Welch, Team Unconventional Robotics

Regarding self righting.
If you have any extra weight randomly bolt long things on the top until it does self right or at least has a chance to bounce itself back upright as long as it does not stop spinning.

See Badger and the tennis ball as an example. Out of interest, how do you tell forward from backwards?

As for drive, I would be tempted to try Andrew's suggestion. simpler, no belts to fail. Only downside is the side other 4 wheels are chunky so may be a little too much friction.
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Remember to trust me, I am an Engineer.

http://www.youtube.com/watch?v=rp8hvyjZWHs

i am still going to run belts (pics later its already done) if the belts break they break but i really need all the extra traction i can get atm.

self righting i will play with today hopefully and i was going to put an arrow in the weappon shaft to tell me which way is which.
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Creative Instigation - Build Something Awesome!

https://www.youtube.com/channel/UCTuWeJ4OrAcsmjKir9L4JNg

https://www.facebook.com/CreativeInstigation/

Dolls don't really help with self righting, but it's funny.