20" hub cut to 16" Will it work?

[docnjoj]

Awright! Calling all U Mechanical /welding experts! I already did this! So there is no going back! I got two identical hubs dirt cheep years ago, and I want to make one a 16" wheel! The other stays as is! Can I weld the cast ally hub motor to the ally rim? They are obviously different kinds of alloy but both aluminum?

 

[TylerDurden]

If the hubbie has covers on both sides, I suggest making flanges for spokes, to sandwich under the covers. I guess you could even on a side without a cover.

Getting the hub centered & true in the wheel will be tough if you weld.

 

[docnjoj]

Maybe a good alternative I Im old and impatient!!!! I could even weld one rim on each side! But I wanna do down and dirty, even if its not perfect. I dont need to center the wheel, as I dont use a rear brake, just the two front discs. Could this feasibly be done???????? Will the welds hold???
otherDoc
Edit Yup! The hub does have both sidecovers! Its a regular 408 brushed.

 

[TylerDurden]

Yeah, but who wants a wonky wheel going bump-bump-bump?

You could also use the motor to drive a chain, ala stokemonkey...

 

[docnjoj]

Could not a really good TIG welder get it right if I did the setup and fixture???? I know such a person! This could go on the back of my grandsons CX24 build up, so it would have to be reasonable true! Chains too complex for the lazy old guy! But Stokemonkey style could be possible ifn this doesnt work!
otherDoc

 

[TylerDurden]

Jigging it up is the trick... it needs to be centered radially and axially. When it's done, you are set in stone.

You can do the flanges with home tools, as the spokes can compensate for irregularities... hell, you could even make artsy-fartsy flanges in funny shapes.

:lol:

 

[docnjoj]

U mean spoke flanges! They could be cut from scrap alloy, but i really have this idea fixated in my head (if the welds could hold)! I wanna do it welded first! If I cant true the wheel after precise welding, then go to the flange for round 2, so to speak Truth is I dont wanna spoke either! Wah!
otherDoc

 

[John in CR]

Sure it can be done. I'd cut/grind down the 3 spokes first to just the right size so the hub center is centered on the rim. Be sure he understands that you don't want to heat up the magnets during welding, so he us sure to properly sink the heat away instead of traveling up the spokes, since AL has over 5 times the coefficient of thermal conductivity of steel and heat will travel quite rapidly up that spoke.

Welding a flange for spokes right at the hub would have be tricky to avoid heating up those epoxied magnets too much.

BTW, we should have gotten together ahead of time, and made it a 4 wheeler. I have the identical pair of 20" wheels w/ a motor. What's the maximum voltage you've run yours at? The smaller wheel isn't going to slow it down nearly as much as going down to 24V would have.

 

[docnjoj]

My wife has the identical motor, but with flanges and spokes! On her 36 volt ping, her Bike-e gobbles up our 8% hill like she is a banshee! She can accellerate up to 18 mph with her brushed 16" front wheel on the hill from a dead stop! Granted she is a bit lighter than me! Some people are using huge volts on BD36 motors wery similar to these ones. I thinksomeone is using 72 volts, but probably not for long Thanks for the tips.
otherDoc

 

[Drunkskunk]

why not weld on 3 tabs to the rim, and 3 more to the motor's spokes, so you can bolt them together. that way you could make minor adjustments in it if it ends up not being perfectly straight.

A realy fat tire would make up for some out of round shape, but not much.

 

[docnjoj]

Thats clever! I have Big Apples on my rims, and they really help resolve "imperfections" in my truing technique Thanks Drunkskunk!
otherDoc

 

[michaelplogue]

http://www.youtube.com/watch?v=jijW310xvp4

 

[docnjoj]

Im impressed! I would try that stuff if wheel failure was not life-threatening. But it might work on the MY1018 noise thread to change the noise characteristics of the pinion gear. I really would rather trust a TIG for my wheel!!! Thanks Michaelplogue!
otherDoc

 

[John in CR]

http://www.youtube.com/watch?v=jijW310xvp4

Michael,

Thanks for the link. It looks like a great way to strengthen the dropouts of an aluminum frame or make changes to an aluminum frame to fit batts or whatever. Of course one would want to get well practiced first, but I'm sure I could quickly learn to do better work than my poor stick welding.

John

 

[Link]

I'd be worried about the rim needing the tension of the spokes to keep it's shape. Seems like one good bump between two of those spokes could bend the rim. :?

 

[dirty_d]

yea what link said, i think the rim will collapse in without spokes all the way around.

 

[docnjoj]

Its a double wall rim, so we will see! Ill keep that in mind, but its only 8"radius. Its on a rear suspension, has a real low pressure tire and its on a tadpole. We will make materials science history soon, hopefully in 1 piece! Thanks for your concerns!!!
otherDoc

 

[ngocthach1130]

You can set up a jig with a use of a band saw. Set it up so the surface have a hole where you can drop the motor axle in and rotate it. Then you can adjust the motor so the point to cut is an exact amount from the saw blade then just by rotating the hub you can cut the 3 spoke to the exact same length. At the same time you might need to look into steel rim or maybe thicker rim. regular rim are meant to have tension equally distributed on all angle or along those 36 spokes. since you'll be moving to 3 spokes you'll need stronger rim for those spots where there is no rim. Otherwise the rim might cave in after a bump.

 

[docnjoj]

Thanks ngocthach1130! I unfortunately dont have a bandsaw, but I do know of a good way to jig it up1 If it works, Ill post pictures. I really believe that at smaller radii it wont be a problem! We will see! Aint science wonderful!
otherDoc

 

[docnjoj]

Im about 3 hours away from bringing the wheel assembly to the welder! Hoping for < 1mm accuracy! Thats better than all my other wheels! Pic when if finish the jig!
otherDoc

 

[docnjoj]

It dawned to my prehistoric brain that the magnets are on the stator, far awah from my workbench! Tylers flange method actually could work, cause the only heat problem is keeping the coils cool! Well, Im too tired to think about alternatives right now. Brief break, then back to work!
otherDoc

 

[docnjoj]

Jigged up, glued down and ready to go to the welder! At the moment, , < 1mm runnout and roundness! The outside humidity and car A/C could change this! Wish me luck.
otherdoc

 

[TylerDurden]

Looking good, Doc!

As long as you're getting welds, perhaps some tabs/gussets on the hub to attach inserts... to fill the openings and support the rim.

 

[docnjoj]

Good idea! Mark the welder said he will stitch weld first, then fill and then smooth with really low temp stuff. I have little fear that the rim will collapse, but I coulda gone for a ride on the Titanic if I were around! I'll give him a call!
otherDoc

 

[docnjoj]

I just ordered 2 torque arms from EV Tech. Since I may go to 48 volts and my wifes bike doesnt have one, it seems prudent at this juncture! They are now $20 apiece, and well worth it compared to that crappy Crystalyte one I spun!
otherDoc