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Killer Toys Presents - Chucky -
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assassin



Joined: 27 Jun 2004
Posts: 1105
Location: SunshineCoast


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The arm stops onto rubber bumpers just before the ram hits the end. So they sort of finish together.
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Post Sat Aug 08, 2009 8:52 am 
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assassin



Joined: 27 Jun 2004
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It doesn't seem like much progress, but I got the main bore of the ram done this weekend. Which I'm happy to have got done with the time I had.


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Post Sun Aug 09, 2009 6:47 pm 
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assassin



Joined: 27 Jun 2004
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Location: SunshineCoast


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Please look and digest. This is the solution I have come up with to fix my drive assembly.





The large part on the left is the hub for a colson wheel, it mounts into a bore in the wheel and fixes with the screw holes(the ones on the outside of the flange).

The pulley would be machined from timing pulley stock, and mounts to the hub with those screw holes(the inside set of holes).

The 1/2 inch shaft on the right is the drive shaft from the dewalts, and is captured by the design of this assembly.

The bushes would be machined from stock.

If you need to, go back some pages to look @ how this design fits into the bot.

Anyone see any problems with this design? Thanks guys.
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Post Mon Aug 10, 2009 9:19 pm 
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Nick
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Joined: 16 Jun 2004
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OK, here is my list of concerns:

The outer bearing is quite large & its running on an aluminium axle. The surface speed is going to be relatively high and I'd be worried about wear and galling on the aluminium. The 'best practice' would be to shrink a thin steel ring over the aluminium to increase its life.

Running a keyed shaft in the inner bronze bearing is going to reduce the bearing life a bit. Probably not an issue here.

That huge flange on the inner bearing will be a pain to make. I'd either make it much smaller or make it in two parts - it won't make much difference if the belt rides off the edge of the pulley a little. Come to think of it, there is little reason to make the outer bearing in one piece either.

In an impact or when you flip a bot, most of the force is going to be taken on the outer bearing. could you make it wider, possibly put in a needle roller and then do away with the inner bearing completely? The inner face of the pulley is going to be very close to the output bearing on the Dewalt and just keeping a thrust bearing between the pulley and motor will keep the belt in place. I think this would make aligning the bearings simpler and increase the strength of the module. It might even make it a bit thinner.

The colson hub looks a bit thin, what is the wall thickness? It looks like it could be bent if the wheel was hit by an undercutter. Is there any chance of running the pulley right into the wheel? I would keep that central stub as short as possible, you want the steel axle and key engaging the pulley as much as possible.

In the pulley, move the key way so its between screw holes - more wall thickness that way.

It looks a bit time consuming to service - getting a belt replaced or replacing a bearing could take a while.

Post Mon Aug 10, 2009 11:07 pm 
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assassin



Joined: 27 Jun 2004
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Location: SunshineCoast


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Jesus Nick, nice second wave of thought about the design there, thanks. I'll print some pictures off and go over the design tomorrow while @ work.

I don't think the dewalt gearbox has a bearing @ the output, this would be my first issue I would need to verify before looking into some of the ideas you mentioned. And If it hasn't wouldn't it need the double bearing support?

Yes the bushes could be 2 pieces.

Yes the outside bearing has a large surface area, I like your thoughts on improvements, and will look @ it and any others.

Other small things you have mentioned I will correct and/or check.


Thanks for your input, it makes things a bit easier and fun, cheers.
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Post Mon Aug 10, 2009 11:27 pm 
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Nick
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Joined: 16 Jun 2004
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I hope the input will be useful, its an interesting design. Ask Glen about the dewalt output; I think most US bots run without an inner bearing. The splined shaft is not a tight fit, but having a wider output bearing would hold everything in place and lined up.

Post Mon Aug 10, 2009 11:33 pm 
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assassin



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Glen I command your eyes to look this way Shocked hehe

Glen, do you know about the output of the Dewalts(In reference to the info above)?
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Post Tue Aug 11, 2009 7:43 am 
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Glen
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hahah its 10:16 so excuse me if im answering the wrong question (thats like 4am for me basically Laughing ) tell me if i am Very Happy

the output shaft/last stage in the gearbox just sits inside the plastic hole and team delta mount and its a very loose fit. the gearbox binds up alot if you bend the axle at all which is why cobras setup was so bad. the frame bent and bound up the last stage quite alot. so id definitely have a bearing bolted to the face of the gearbox housing as close as possible to it if only to keep it aligned.

i wanted to recess a bearing into the team delta housing itself and eliminate the inner bearing cutting out 10mm of width which would be entirely possible. it would just have to be a thin one (6 or 8mm i cant remember now).

looks like there will be a pretty massive load on the wheel as well, when you fire the flipper arm. you might even risk snapping the shaft as it is hardened to a pretty high degree iirc.

i would probably be inclined to make the bearing support go on the outside of the wheel assembly and just use bigger diameter pulley stock - looks like you easily have the room for it - and machine the hub out of the one piece then use a bushing/bearing on the inside outside. not sure how it would affect how your armour bolts on tho! but with that setup changing a belt looks like a nightmare.

not sure how well bushings take thrust loads either? im guessing probably not very well.

i noticed your using the $50 carbide tools as well (?) the boring bar in them is damn good hey! i ended up buying 5 of em and ground them down to make a few really small ones. soooo handy!
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Post Tue Aug 11, 2009 10:31 am 
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maddox



Joined: 21 Dec 2006
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Location: Belgium


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Just short sentances, as I'm not very awake at 4 50 am.

I prefer the Glanze cutting tools.(with hardmetal inserts) A tad more expensive, but of very good quality, stability and ease of use.

On the pully/bearing/bushing issue.

In my machines I try to use a dead axle as much as possible.

Bronze bushings take trust loads "ok", as long the running surface is smooth and at a 90° angle to the mounting surface.

Post Tue Aug 11, 2009 12:51 pm 
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Nick
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Joined: 16 Jun 2004
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DOH! I just typed a huge post and lost it when Firefox crashed! What is the Colson wheel you are using - I will do a quick sketch of what I am thinking for a new design. Short story, Glen's ideas are right on the money.

Post Tue Aug 11, 2009 10:29 pm 
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assassin



Joined: 27 Jun 2004
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Cool, thanks.

http://www.robotmarketplace.com/products/0W-BPDWC06.html

3-1/2 x 1-1/4
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Post Tue Aug 11, 2009 10:54 pm 
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Nick
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Cool, that's what I guessed from the CAD pictures. Are you using 1/2" belts? So far the big bearing, combined axle/pulley is looking fairly plausible, could be used in other bots too. Would it be a problem if the outer bearing block was a bit higher than the Delta mounting kit (IE over 2" high?) Gotta sleep now...

Post Wed Aug 12, 2009 12:52 am 
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assassin



Joined: 27 Jun 2004
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3/8 inch belts

The gap @ the moment is 10mm - 15mm - 10mm, for a total of 35mm.

The total height is about 67mm, and the axle height is about 29mm from the bottom.
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Post Wed Aug 12, 2009 7:42 am 
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assassin



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Looks like most of the load would be on the outside bearing, but there would still be load on the inside one.
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Post Wed Aug 12, 2009 9:23 am 
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Nick
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Sure, the inner bearing is going to take some load, just less than the outer one. For instance, the very successful Whyachi TWA40 has a large 1" od front bearing and a tiny 5/8 od, 1/4 id rear bearing. this gearbox powered many winning 30 and 60 lb bots for years. If the rear bearing in Chucky is a light duty 1/2" id bearing, that should be fine.

Post Wed Aug 12, 2009 7:31 pm 
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