Specialized 29er hardtail - 6374 motor, sprocket reduction

This is the beginning of my "chain bike," or so I have named it as it runs a two stage chain reduction to the rear wheel. I first tried a friction drive, but had some problems with tire wear and durability. I decided to switch to chain drive for increased power capability along with less tire wear (I prolly could have adjusted the fd for less wear, but I wanted a chain drive anyway).

So I start with a leaderhobby 6374 170kv outrunner, CC HV80 esc, 6 Turnigy 4S 5000 mAh hardcase lipo, and various servo testers and other parts for battery charging etc.

I just ordered two #25 sprockets for my primary reduction (12 and 32 teeth), two #35 sprockets for the secondary reduction to the rear wheel disc brake mounts (10 and 83 teeth), and an ACS 16T freewheel with 1/2" shaft adapter from staton-inc.

I still need some chain...Any good places to pick up chain? I need some #25 and some #35.

That gives me 29.42 mph no load on 12S lipo at nominal voltage. Or 19.61 mph no load on 8S lipo. Pretty slow for now, but I plan on rewinding for higher kv at some point or maybe getting sensored ebike controller and running 16S.

I was planning on bolting the 32 tooth #25 sprocket straight onto the freewheel, but they have the same pitch diameter, so we will we see how that turns out. Other stuff I have to make include: adapter for disc brake mounts to large 83 tooth sprocket, mount plates for the motor/jackshaft, and seat tube clamps for mounting the whole thing.

My plan for the bike is attached. I did it in MS paint. I have a xl frame; I'm not sure about the one pictured. The top green circle is the motor, the bottom green circle the 32 tooth, the large green circle the 83 tooth. The black rectangle is the battery box mounted to the water bottle holders.



Any helpful comments, critiques, or suggestions would be greatly appreciated.

I shall assume that the motor and reduction will fit in where you have them, as I don't have the bike here to check, and I will also assume the reduction maths is correct. But what really sprung out was the sprocket sizes, the tighter the chain needs to bend, the noisier and less efficient it becomes, to a certain extent. You also increase the chance of it jumping and increase tooth wear.

How were you planning on mounting it to the frame? tube clamps? and the batteries? that battery pack looks small, you have about 200wh so that will not give you much range, how much were you wanting though is the question. Apart from that, it all seems feasible and could be done without to much trouble, unless there is something I am not seeing... So good luck! just work out exactly what needs to be done before you start building/buying the stuff, it will save time and money.

Will be good to see the finished thing, so go for it!

Prong,
If you have a tractor supply store nearby they stock #35 in bulk. After that is an Ace Hardware store. (they allways have links but some don't cary the actual chain)
For #25 I will 2nd recumumpences recomdation for the heavy duty stuff from here:
http://www.electricscooterparts.com/chain25.html
Be sure to get the heavy master link's to fit the chain....premiumn #25.
Check your pm for options.

By my calculations you need a total of 14.5-1 reduction for 30mph on 29er wheels, running 30 volts nominal. 3-1 primary reduction will need 13/63 combo on the final drive for 4.5-1 final ratio.

If your only riding on-road, you can make this work. If your going off road, I would recomend gearing for 18-20 mph top speed. Your little motor& speed controller will thank you.

bandaro said:

I shall assume that the motor and reduction will fit in where you have them, as I don't have the bike here to check

Click to expand...

Yes they do.

But what really sprung out was the sprocket sizes, the tighter the chain needs to bend, the noisier and less efficient it becomes, to a certain extent. You also increase the chance of it jumping and increase tooth wear.

Click to expand...

Good point, we shall see. I did choose to put the 12 tooth pinion on the motor shaft and the 10 tooth on the jackshaft thinking that the chain speed would be lower on the jackshaft so the noise, etc. from the 10 tooth pinion would be more manageable. IIRC recumpence used a narrowed 10 tooth #40 pinion on his jackshaft for his catrike. Here is the thread: http://endless-sphere.com/forums/viewtopic.php?f=28&t=22483&hilit=10+tooth+freewheel+recumpence.

How were you planning on mounting it to the frame? tube clamps? and the batteries?

Click to expand...

I was planning on drilling some holes in UHMW plastic, but now I may have a better option.....

that battery pack looks small, you have about 200wh so that will not give you much range, how much were you wanting though is the question. Apart from that, it all seems feasible and could be done without to much trouble, unless there is something I am not seeing... So good luck! just work out exactly what needs to be done before you start building/buying the stuff, it will save time and money.

Click to expand...

Thank you. I already bought most of the stuff, but I have been planning this bike since November so hopefully it goes well the first time. The battery is 12S, 10Ah lipo so 444 Wh although discharging to 80% would be 355 Wh. Hopefully enough to get about 15 miles riding conservatively and pedaling a lot.

Thud said:

Prong,
If you have a tractor supply store nearby they stock #35 in bulk. After that is an Ace Hardware store. (they allways have links but some don't cary the actual chain)
For #25 I will 2nd recumumpences recomdation for the heavy duty stuff from here:
http://www.electricscooterparts.com/chain25.html
Be sure to get the heavy master link's to fit the chain....premiumn #25.
Check your pm for options.

Click to expand...

Thanks for the help. I responded.

By my calculations you need a total of 14.5-1 reduction for 30mph on 29er wheels, running 30 volts nominal. 3-1 primary reduction will need 13/63 combo on the final drive for 4.5-1 final ratio.

If your only riding on-road, you can make this work. If your going off road, I would recomend gearing for 18-20 mph top speed. Your little motor& speed controller will thank you.

Click to expand...

I have a 22:1 reduction so hopefully enough gear down to help my little baby motor and esc survive. I will likely pedal to 5-10 mph and be pedaling constantly before hitting the throttle as I am quite fit (high school xc runner). The bike is mainly for the road, but once I put some miles on it I wouldn't put myself past taking it out on some trails.

Well it's been a couple months, and I've VERY slowwwwwly been working away at this bike. News since I last posted:

Thud very kindly offered for me to be the beta tester for his new simple reduction drive, and I accepted. Although I haven't yet tested it, I'm sure it will work wonderfully.
All the parts that I ordered came, so eventually my brother will also have an electric bike once we get a new motor/controller/more batteries. We plan to bike to school together (~8 miles one way).
Three finals down, two finals to go; school is almost out which should give me more time to finish this bike, deliver Thud his long overdue review, and get out riding in the nice weather.

Here are some pictures of how the bike looks now:





And this is how my motor currently looks after four hours of fiddling:


Things still left to do:
finish battery box
press shaft out of motor bell and insert new one in
reassemble motor
mount sprocket to rear disc brake holes
buy #35 chain

Looking good!

cant wait to see it finished

I really like that bike

Looking forward to the review. Would also like to get a Thud unit, nice job!

How much longer before we get the beta test of Thud's RC reduction drive????????????????????????

Come'on & get some video to post too.

Thanks.

I finished the bike yesterday and was able to ride it around. It worked very well and was much more confidence inspiring than the friction drive I had earlier. Some initial comments:

the chain guard is hard to install once the unit is on the bike
I was not able to get all the screws for the disc brake sprocket mount fully inserted, only 5 would go in
the unit is narrow enough to not present any problem with pedaling
it is quieter than I expected

Some things left to do:
Increase voltage to 12S
Play with slipper clutch - I did not notice it coming into use, but I was not really paying attention to it
Tidy up batteries, maybe put into bags that hang over the top tube up near the handlebars
Install a real throttle (not just use servo tester)

Pictures to come once I get onto a real computer. Review also to come shortly.

For a beta test I think there should be some video too... how can we understand how the bike/drive moves & sounds without video?

Don't worry deVries, there will be video too. Maybe I can even borrow my friend's gopro.

Well the bike has been mostly finished for a couple months now, haven't been riding it that much since x-country season got into full swing. Now it's winter....

Anyways I thought I'd post up a couple pictures of its current state. It's fairly clean and tidy right now, but I'd still like to add a cover for the batteries, probably out of nylon fabric or something. I also need to solder up some new wiring harnesses that will allow me to parallel the packs before they are put in series as opposed to the way they are now (series then parallel). I'm currently running 12S right now for a top speed of about 25 mph. Getting the throttle working instead of just using the servo tester definitely made the bike much more fun and much safer.

Thud's reduction unit has been working fairly well so far. The large #25 sprocket on the jackshaft is not exactly centered, so the chain tension on the motor side fluctuates a bit. In addition, I'm having trouble working the inner diameter of the small #35 sprocket connected to the freewheel large enough so that it can freewheel without rubbing on the jackshaft. Otherwise, everything is working great, the bike is a lot of fun, and I think it looks pretty good. I'll try to get some video in the next couple weeks; the season is finally over, and I should have a little free time in the coming weeks to get some work done on the bike.