[FW] Wedge Spinner in time for Robo Challenge champs!

[Giles]

I think for the sake of maintaining momentum I will stick with my timing belt plan in this case. I also have a ton of castor wheels to use that won't mount very easily to any live shaft, but are perfect for dead shafts. See Edit.

Tonights progress, mainly focused on a new layout, fitting things in better and overall design considerations.
f4dcb549081ac3569b6ec890f2ee82b8.png03dc01d309d91152d78494fab7e99a4e.png

Edit! Just saw that thread about making your own hubs from linear bearing mounts..... that seems like a real nice option! Would I need a keyway as well? Or would it clamp tight enough as is? Maybe that is a better solution than the belts after all.

[Flag Captured]

I don't think the belts are necessarily needed, the saturns are excellent bits of kit and they'd handle it easy enough

Personally, I'd maybe look at moving the wheels back so it drives a little better - you might want to have a look at the US bots 'Riptoff' and 'Also Riptoff' for a bit of inspiration - they're both similar to Overdrive of mine from last year... But we don't talk about Overdrive haha.

Other than that, everything looks pretty good there!

[overkill]

Just to be different, I like the belt arrangement! It gets the wheels closer to the centre of gravity and should improve traction and driving. The problem I see is with the weapon; having the pulley between the disks means you have a long & unsupported shaft on the motor and that can cause a stress when the disks hit something and stop suddenly. Someone had that exact failure last year - the shaft snapped at the front of the motor and they were out of the competition. If you made a single disk that was twice as thick and mounted the pulley at the end of the shaft, you can have a much shorter motor shaft with the drive pulley right up against the motor, where it won't cause problems. Having a single disk will be much stronger and probably less work to mount. Are the disks running on a fixed or rotating shaft?

[Giles]

This was also a concern of mine. The bulkheads are 15mm and the motor shaft is 23mm.. Leaving me with only 8mm for mounting the pulley. Is it easy/recommended to replace the outrunner motor shaft?

I'm building the disc from a sandwhich of 4 thinner discs, because that's all I've been able to source from kcut. So I could arrange them to have the pulley at the side.

[overkill]

You can buy a short length of silver steel the same diameter as the motor shaft and swap it in. On most motors there is a small circlip on the shaft at the front of the motor and this is where it almost always breaks. Removing the circlip lets you pull the shaft & endbell off the back of the motor. The shaft is held in by a couple of grub screws and usually lots of friction, so you need to loosen the screws and tap out the shaft using something with a smaller diameter. You need to grind a flat on the new shaft to match the original so it can't slip after you assemble it (it can be shallower and rough-as). The new shaft will probably be better quality steel and won't have the circlip notch, so it will be much more reliable. The other thing you could do is mount the motor on a thin plate and mount that to the inside face of the bulkhead so you can get the pulley closer to the motor. Personally, I would do both but time is running short.

[typhoon_driver]

Also watch out for any small washers that are on the shaft and make sure that these go back in the places they are meant to!

[Giles]

Thanks guys, will look into doing that once I receive the motor in the mail tomorrow and assess how it all goes together. Just got a quote back from kcut for the hardox discs and the price is much better than I expected! Happy days! I'm shopping around now to see if I can find a watercutting place with 15mm grade 5 titanium in stock to cut my bulkheads once they are finalised. I've tried a few places and I am awaiting replies, does anybody have suggestions?

Another question I have is about armour. How thick/what material are most using for armour? Im not sure if steel or titanium is better or other options. I know HDPE is popular, but I think I want to go the metal route.

My thoughts so far were: 5mm hardox wedge and some kind of steel of some kind of thickness elsewhere...

I'm also going to use these instead of bearings for the disc now:
http://simplybearings.co.uk/shop/Bea...duct_info.html

I noticed they have only got 2mm wall thickness though - will that be ok? I've been told that they are pretty durable compared to other options.

Sorry for all the questions... millions of thoughts flying through my head all at once..

[overkill]

15mm internal bulkheads that's even more over-engineered than something I would make! If you are set on that for some technical reason, add plenty of cut-outs to keep the weight down. I would seriously think about a tough aluminium like 2024 or 7075, which will be cheaper and easier to source. Titanium makes great armour but it is harder to fabricate and is by far the most expensive. The 8mm armour on my bots is considered stupidly thick and has held up well over the last three years.

You will get lots of conflicting answers about those bronze bearings. Personally, I have seen too many of them fail but it depends on how fast the weapon is spinning and how hard it hits. Since bronze bearings are so cheap, buy plenty of spares and consider them a consumable. You don't really need the Oilite bearings; they are meant for low maintenance situations and you are better off with a harder solid bearing and oiling it regularly. I would go for a thicker wall if possible, particularly as you have a stack of thin disks and if just one of them takes a high impact, its going to exert a huge amount of pressure on a small part of the bearing.

[Giles]

Haha, and there I was thinking "I hope 15mm is thick enough!" Say I dropped it down to 10mm thick, would aluminium still be good enough for the job? I would much prefer to work with alu than any other material, but I'm always concerned over it being strong enough.

[overkill]

It depends on how the parts are held together. Assuming you are drilling & tapping the aluminium for screws, I would keep it thick and add some cut-outs to reduce their weight. For internal parts that don't take direct impacts and need high tensile strength (the bulkheads supporting the weapon) 7075 or the similar Fortal aluminium alloys will do a great job. There is an even stronger alloy available in the UK but I can't recall the name - Mouldy used it in 722.