More information please.
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So even the rain that falls isn't actually going to fill our dams and our river systems

ok so this version has been retroactivley redubbed the Mk0

zoom
radio is a HK $29 special
ESC's are fingertechs
brushless controller is a turnigy something or other (50A i think, cant remember)
rhino 40C(i think) cells 1Ah

The weights came out pretty close, the teeth were a little smaller than I had hoped at about 200 grams for the pair.
Most importantly the concept was validated with the ring staying totally round throughout the matches. The reason the center fell out of the bot was the bearings getting smashed up (as you can see)


zoom
and


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These were VXB 6mm ID bearings, I went through 10 on the day.
some of them got flat spots on them as well so they weren't too brittle, the forces were just far greater than I expected.
Supporting the 6mmID bearings is a 4mm thick flat that runs to the wall, this is a distance of about 10mm. The bearing mount was bent over this distance and the mounting shafts were also noticeably bent.
You can see the groove the bearings run in (just) in the ring on the left of the first pic. With the incredible find of sewing machine oil on the day of the event it ran ok with no noticeable wear though it was black with Al juice after each match. After the first bearing explosion I had to pull bits of bearing out of the ring, then smooth it with a file. There were no noticeable dents in the ring which was a pleasant surprise.


You will also notice the metric ass tonne of kapton tape just behind the motors, this is because there was about 1mm of clearance on the motor power leads, I had to press quite firmly to get the motors to go into their mounts as the angle they needed to go in on made them too long to sit straight down.

The wheels are made of foam kickboards sliced up and lathed to be somewhere near true, minimum ground clearance was a priority but it also needed to not touch the ground when it was running so nylon screws were used as skids.

I had some difficulty getting O rings of a suitable size for the friction drive, eventually I wound up with some imperial size to get the right thickness. Originally I planned on using a pair of O rings but the friction was too great to get the motor to start reliably, so I dropped it to just the one. The other function the O ring provided was to make the ring sit on just 3 bearings, without that it would rattle around all 4 and lose heaps of energy when spun by hand. The total tolerance for the bearings and the rings was .25mm.

I'm a little lost for how to improve it at this stage, Obviously larger bearings would be nice but could be hard to fit into the weight and size limit. To address the bending some kind of top support is required. Perhaps make the bot in 2 halves clamshell like. I would also like to reduce the height, the motors are what defines the height in this one. I'm thinking of using the ant sized motors and going to 4WD. As for the weapon drive motor, I'm hoping to ring the inside of the ring with magnets and in between the bearings make up a brushless motor. The varying air gap will mean the efficiency is terrible but hopefully it won't bother the brushless controller too much.
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Mechanical engineers build weapons, civil engineers build targets

How about using precision needle roller bearings? They have a thicker outer ring and are far stronger than the sam diameter ball bearings They would add weight, but are the best bet for fixing the impact problem. This is the smallest one I can find: http://www.mcmaster.com/#cadinlnord/2423k21/=kmxsa4 Note the 890 Lbs dynamic load capacity - at least double the same diameter ball bearing!

Saving height & weight with smaller motors sounds like a great idea. The Spark silver motors with the larger gears might be a good choice. The B series motors from RMP would also save some space if you still like 2WD.

It's also worth noting that steves fbs somehow gets away with 100:1 antweight drive motors and little wheels.
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YEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH

that's what had me thinking ant drives as viable.
I might look at putting some bearings in there for the wheels too ;->

The blue foam is good in that about 3kg crushes the tyre until the body hits the ground so it should minimise the shock loads to the gearbox.
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Mechanical engineers build weapons, civil engineers build targets

You could probably gear 3-4 antweight gearmotors together onto a single output shaft and have less weight. You could also then wire them in series to allow you to run higher voltages.
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https://www.halfdonethings.com/

weight isn't the issue with the current motor, I want thinness, that way i can make the dia of the ring larger.

So 4 standard ant gear motors will hopefully do.
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Mechanical engineers build weapons, civil engineers build targets

I reckon if you put a little belt drive or gear drive onto 4 of them and support the wheels with bearings the ant drives will work fine. Its the mounting in my robot and the fact that the forces on the tiny shafts are huge. I was considering making something like this but just replaced the gearmotors for the moment.
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Steven Martin
Twisted Constructions
http://www.botbitz.com

looks like an awesome design.... all milled out and everything...and that outer ring is thick as
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Miles Blow - Julie Pitts
www.mulesfilm.com.au
www.wombokforest.com.au

-Pickasso- Vivid Sportsman champion 2015

Ok shredder mk2 probably isn't going to happen by this event.
It was always going to be close, but yeah holidays and work happened.
So here's where its at.

Changes from mk1
608 bearings, aka rollerskate bearings.
that should stop the "bearings explode on impact issue".

Bearings will be mounted into a clamshell chassis, this should stop the, "bend the crap out of the super sexy looking chassis on impact" issue.
tossing up if I put a steel shaft through the bearing then mount that in the top and bottom clamshell parts, or just put a bolt through the mount and use the aluminium to stop the bearing from twisting out.

To accommodate the larger bearings the inner part of the bot has expanded by 12mm, I'm about to work out what that does to the ring. I'm going to expand its Z axis by 2mm as well just so there is some breathing room inside it. This one should actually have room for the tabs on the back of the motor, and crazy stuff like wires.

curvy inner ribs that are less than full height just to stiffen it all up.
some nice beefy mounts in the centre for attaching the clamshell parts together, M6 screws. Also the bearing mounts will attach the clamshell halves together, haven't quite decided the best way yet.

Motor mounts are now separate plates, the mounts will also act to tie the halves of the clamshell together. (thinking M5 screws at this stage)
Might look at making a pocketed mount in the middle of the bot to support the motors, mostly because it'd look cool when its cut out lol.
Need to have the mounts as a separate piece otherwise the halves of the clamshell would be different and that just gives me the heebey jeebies.

Same wep motor, that seemed to work ok last time, the one in here is just a placeholder. I might look at going to 3 cells though, just for the lulz.

Half the clamshell weighs 46 grams at the moment, needs a bit more for the bearing mounts.

From action aluminium 160mm x 50mm round bar is $30+gst
220mm x 50mm round bar is $50.60 +gst
and in theory they have them in stock.



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Mechanical engineers build weapons, civil engineers build targets

If action don't have it go to thyssen krupp just up the road, they have 7075 grades there.

+ not done in time what! There's at least a week to go so lazy
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

7075 grades you say.... interesting.
Their website is craptacular do you have contact info for them?


There is a whole mess of machining in that one, way more than in mk0 :-<
There is like a solid day of CAM in it alone lol.
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Mechanical engineers build weapons, civil engineers build targets

There's no website to speak of, just call em. The guy i talked to was surprisingly helpful (02) 9757 7777 Address is 7-10 Denoci Close, Wetherill Park NSW 2164

http://www.thyssenkrupp.com/en/standorte/detail.html&orga_id=303216
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

The new design is looking excellent! How about mounting the bearings on an offset bolt like this:



That would allow you to adjust the bearing fit if anything got bent out of shape.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

My robot....bend????
THE VERY IDEA!

Actually something like that isn't a bad idea.
If something does bend I think the frame will be toast anyway but it'll help with manufacturing tolerances at least. I'll see if I can work out a way of putting it in that doesn't rely on friction to stop the thing from rotating on a big hit.
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Mechanical engineers build weapons, civil engineers build targets