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

[Giles]

Myself and team mate Dave have been slowly tinkering away at a crusher bot for the champs.... but we've realized the champs are VERY CLOSE now and our hydraulics isn't going to be sorted in time. So, we're going to work our asses off to make a more simple design - a wedge/small spinner.

Dave has been working on a custom ESC for the last month or so, and will continue to do so for the coming weeks. We wanted to do this as a challenge, and considering the work we've done on it so far, we don't wanna quit! If this turns out to be an epic failure, we will fall back on more tried and tested ESC's. Will post more about this later.

I've been doing a bit of CAD work, with hopes to get the whole bot designed by the weekend and have parts being ordered early next week.

First I started off with a simple box with a pair of Ellis' mighty fine gear motors and some castor wheels:
f6458b9f9f08ee52cc333dbad1f44c88.png

Then I designed & balanced a single tooth disc:
1516c2158743d49c8fc60fd90532bad6.png

Then I made some mountings for it, which will hold the weapon motor, belt drive and dead shaft axle:
6993b28672cfbdfaa5e64a310c7abbe7.png

At this point I realised it was rather long and making bad use of space, so I took it into photoshop and sliced it up into a more appealing layout. Will implement these changes in my cad file soon:
383da1c99c5b3877c2d44a8ae631819c.png

As you can see, we don't have much, but hopefully that will change in the coming weeks! This is technically my second ever build (disregarding the half-started crusher), so I will no doubt need to ask some annoying questions to you all along the way!

[Eventorizon]

Any reason why you are running another reduction off the Saturns? I don't know your wheel size or voltage but I can see that being very slow given direct drive off the Saturns is fine as it is.
Aside from that, doesn't look bad :-)

[Giles]

I was thinking about this on the train to work this morning I think the belt drive will actually be a 1:1 ratio, using HTD5 timing belts. The belt drive is just so the wheels aren't directly attached to the motors, to offer some protection.

Edit:
I just realized you have been replying to my facebook posts! Thanks for all the input so far mate.

[Rapidrory]

It would be easier to just drive the rear wheels directly from the Saturns, and then have a single belt drive either side from the rear wheels to the front wheels; the saturns are built for combat, and unless you're using solid metal wheel hubs or something, the wheels will likely give way before the gearbox if they get clipped by a spinner. Plus at the rear of the robot, they're usually fairly well protected by the front of the robot :L

[Giles]

I agree with you if i'm honest. But the biggest problem I can see is the making of the hubs. I don't have much in the way of machinery/tools, so I'm pretty limited to 2D laser/watercut parts or 3D printed nylon parts, or whatever I can cobble together from bits and bobs. Unless I can think of an easy way to make/find a hub with a keyway and grub screw that fits the saturn drives, its easier for me to do a belt drive. For the belt drive I can order a timing pulley from belting online, have them bore it out to size and add a keyway and then make a nylon/alu hub for the castor wheels myself.

Extremely open to suggestions on alternatives btw, I'm just trying to be resourceful with what I have access to!

[daveimi]

I have been wondering if there are any off the shelf wheel solutions for the saturn motors...

[Eventorizon]

I just realized you have been replying to my facebook posts! Thanks for all the input so far mate.

No Problem

So far as I know there is no off the shelf solution for the Saturns right now, which is a problem for you but I know Ellis is on it. Aside from making your own wheels from HDPE, Bike Tyre and then either filing a keyway in the plastic or going with grub screws I cant think of any fast and dirty solutions... then again I don't really do fast and dirty.

[harry hills]

I've got 6 keyed 100mm blue casterwheels should anyone want a basic setup.

[maddox10]

I use a Hex 17 on the shafts and fit a large scale RC wheel on them.

[shakesc]

Have a look at this thread for ideas

http://www.fightingrobots.co.uk/thre...908#post434908

[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.