naynay12

Hello all have not posted about my build in a while.Well the hpi 2 speed did not hold up ,and after about 5 tanks and cast gears has chipped,even though it has worked in the past,only with smaller engines,my engine is 26cc.
So now im going to use sprockets with #25 scooter chain.My original ratio was 7:5:1 with the transmission,and it has heaps of torque,though was not very fast.Now im goign with a ratio of 6:1. Six inch tires.
Just want to see if anyone can come up of anymore ideas of how to mount this sprcocket to the diff cup.I have a few ideas in mind,but just though i would see if i can get any brighter ideas?

Mudgy

machine the end of the drive cup 45 degree bevel.
Centre the 2 components
Mig or Tig weld the sprocket to the cup - tack welds first at 3 points
(otherwise welding from scratch will warp the job)
check (after tack welding) if all is true/plumb
bead weld the rest of the job.
any "dags" can be machined off

That's how I would stick it together

Dirty_Vinylpusher

Damn, NayNay....
Next time use a more neutral background when you take photos like that....

Seriously though, unless you REALLY know what you're doing with that welder I'd take it in to some engineering/welding/mechanics shop and wave a sixpack (of beer) in front of them and ask them to stick it together for you.
At least then you'll know that it gets done properly and that everything lines up and is straight/square/perfect.


Just make sure they do the welding before they drink the beer.....

RCguru09

I would scrap that idea and just go all chain. It's cheaper and you wouldn't have to weld anything to the shaft.

naynay12

i know someone that welds i might get the to do it for me...
lol dirty vinylpusher i didn't realise the pic were like that until i viewed them on the computer [:-]

sam123

My Feedback: (1)

Hmm you might have a bit of trouble getting that sprocket machined since it is most likely hardened. The one I have definately is. Maybe you could get someone to machine away at the part of the diff cup coming from the side that contains the grub screw, so that the sprocket can slide over and lock onto the drive cup through the top of the grub screw slotting in underneath the flat spot of the sprocket bore.

sam123

My Feedback: (1)

Welding should only be your last resort. A mechanical fit will be more than strong enough, and will most likely end up being more accurate.

Dirty_Vinylpusher

While I agree with this, even if you were to machine the cup, how is the sprocket supposed to stay where you want it to?
I don't see a grub screw on it. (the sprocket)
I understand what you mean when you said
the sprocket can slide over and lock onto the drive cup through the top of the grub screw slotting in underneath the flat spot of the sprocket bore. ,
but I don't see how this will keep the sprocket from moving sideways.


Personally I'd weld it.
Actually I'd have it machined and weld it.
If you go overkill at least you know it ain't gonna break.
Unless you wanna keep all the bits non welded in case you wanna use them for something else down the track or if it's the only one of its kind.
This is why I'm spending a bit of money and getting sprockets from a supplier who can get me more should I need them.

Mudgy

General engineering sprockets are only hardened at the outer/teeth. The centre is un treated. This way, machinists can easily alter inner dia. and add keyways.
Welding will alter the properties regarding hardness, but Hobby use is still far less stress than constant industrial stress - what the components (usually) were designed for in the first place.

sam123

My Feedback: (1)

To stop the gear from moving sideways, a small cut could be made into the drive cup, over which some copper wire could be tightly wound. Then, sandwitched between the copper wire and the sprocket there could also be a washer. As long as the two sprockets are alligned, there will be very little if any force trying to slide the sprocket sideways.

Dirty_Vinylpusher

Good thinking dude.

naynay12

Hmmm thanks for the ideas ar i like your idea sam...
This was my main idea...
Drill the spocket so that it can just fit over the diff cup,with no play.
Then get a plain hex nut,and drill it out to the same size as the spocket.
Then connect the sprocket and nut ,probably with a drill,and a couple pins going through them.
Then slide the spocket and nut over the diff cup and secure it with another pin going through the nut and the diff cup...
Its a bit hard to explain. [&:]

Dirty_Vinylpusher

It will probably be pretty hard to do as well unless you have a decent pedestal drill...
Trying to drill out a hole like the one in that sprocket is also a sure way of breaking drillbits.
Not a bad theory though, I see where you're going with it.

If you manage to drill out the hole in the sprocket, and drill out the nut, I'd still recommend welding them two together.
The sprocket and the nut I mean.
Still, a lot of work and I'd still recommend getting someone to weld the sprocket to the cup.

I used to stuff around a lot with things like that.
Adding this on to that and attaching something to it to hold it to something else.
In the end you'll end up spending a whole weekend doing something that can be done in 5 minutes by someone with the right tools.

I'm not dissing your idea, or Sam's for that matter, but believe me, I've been there so many times and have come to the conclusion that it's time better spent solving the next problem.