Giant Stiletto chopper NuVinci build? Thoughts?

[EVnewbie]

Hello All,
I have been studiously reading the reports, concepts, dreams, realities and chaos that is on this board and pondered a few things. Although I thought building up my Norco One25 hard tail dirt jumper would be a good idea, the aluminum frame and the shortness of it cause me to pause. I do have a 2005 Giant Stiletto chopper bike laying around and it seems to be the best format for my first ebike build. The steel frame, it's durability, 180mm rear disc brake and length give me room for screw up....errrr, room to put in what I want.
If you wonder what a Giant Stiletto looks like, here is the link: http://www.bikecyclingreviews.com/Giant_Stiletto_Its_Sharp.html

My first concern with the Giant is front disc brakes and I can have those with the Schwinn OCC chopper suspension forks for $300. They have the 1" steering head I need and will make it look more like a chopper so no harm done. It requires a 24" front disc wheel which I do have, it is a SAS Combat double wall 32mm wide rim with disc and 3" wide tire so that is complete. Have to get the fork before anything else and it is $300 so... hmmmmm.

I have a powerpack BMC motor with 35 amp controller. It was the hotrodded scooter that lived in 2005-2006 until balancing issues with the SVR AGM batteries destroyed the pack. The 36V 35 amp motor screamed and that little scooter would cruise at 23 MPH all day, take the steepest hills without issue and never overheated. I plan on using that for the Giant Stiletto but use a Cycle Analyst to limit the amps to 25 or so at 48 volts.

Gearing, this is the problem. The motor will spin at 3,775 RPM at 48 volts so I need to gear it down so it will be usable. My plan is a Stanton 5:1 gear reduction that uses 1/2 inch thick (13mm) gears riding in a 3 cc gear oil bath for lube and to keep it quiet. Stanton offers a freewheel adapter that fits on the output shaft and I'll run the standard BMX 16T (or smaller if I can get away with it) freewheel.

Since the drive gear is 16T and will spin at 700 RPM max, it makes it critical to step it down yet again. The NuVinci hub has a dual gear setup, one for pedaling (16 to 22T) and the other for a motor at 44T. This will get it close but I wonder if I can change the motor gear for something larger. Maybe I can go with a 60T crank gear and attach it to the 44T? This would bring the max speed of the rear input down to 187 RPM, I can't pedal that fast but the peak efficiency of the motor is at 60% speed so I can pedal that fast. When the motor is at it's peak of efficiency, it calculates out to 27 MPH which is good enough for me. I pedal at 100 RPM which would put the speed at the motors peak at 27 to 30 MPH.

Since it is my first ebike build, but not my first "e build" (the scooter was that) I find the Giant Stiletto to be good for the steel frame and when the chopper fork is added, the thing will be over 6 feet long. Very hard to fly over the bars with a beast like that! My son does not want to give up his Norco One25 and I prefer my Iron Horse freeride bike to remain powerless.

The costs for the build are stacking up along the lines of this:

Schwinn OCC disc brake compatible chopper suspension fork $300
NuVinci 24" wheel with dual 44/16T sprockets $430
Headway 51.4V 15Ah LiFePO4 battery pack (when available) $600
Stanton 5:1 gear box $170
Cycle Analyst with 25 amp external shunt $150
______________________________________________
$1,650

This thing won't be cheap! Luckily I have the bike, the motor, controller, throttle, brakes, tires and everything else I need. Is this a good design? The final rig will run 24x3.00 tires, front suspension and disc brakes all around. The only part that makes it a time constraint is the Schwinn OCC suspension fork, I can get them for $300 now on ebay...but maybe not next week. If I buy the fork, I am committed to the build since my wife would kick my arse for dumping money into something I wont ride.

Am I on the right path, the wrong road, stoned, stupid or should I stay on the porch? I have noted that there is no buzz about the Stanton 5:1 and 18.75:1 gear reduction boxes that they make for 32 to 49cc engines. Wonder why but it is either hub motors or RC motors around here so the Stanton boxes don't fit into the equation. Just wondering...

If it is a bad idea, please let me know...don't want to start buying a $300 fork that I can't use for anything else.

 

[mwkeefer]

Hello,

The stanton might be expensive if you don't already have it... it seems you put a good deal of thought into your design/plan, reusing older parts - good deal.

Honestly I think a person such as yourself could do a nice aluminum mtn bike, you obviously are cautious and smart enough to figure the pitfalls and issues with this install method.

The chopper is sweet! Which color?

I think so long as your rpm comes down as you expect with the stanton you have a nice ride planned. I got to ride my first chopper style eBike the other day and it was a hoot... that's without gearing = )

-Mike

 

[EVnewbie]

Mike,
Thanks for the reply. My problem is I have too many bikes to choose from! The Norco One25 is the bomb-proof aluminum MTB hardtail, the Iron Horse is great for full suspension but they each have their drawbacks. The steel Giant Stiletto is nice since it has a ton of room for batteries, is very long so my son won't endo the thing, my son won't take it off-road and it has the mid-drive axle to play with. Did I mention it was steel and long?
Have not heard any word on the Stanton gear boxes but they look very strong. CNC aluminum boxes that can run gear oil to keep them quiet and long running. Availabe in a 18.75 double reduction or 5:1 single reduction with 1/2 inch thick gears and cartridge bearings for strength. Stanton even has output adapters for spin on BMX freewheels to make the gear reduction simple. What is not to like? I just wonder why other folks are not using them? Am I missing something? The single reduction is $170 with the double being $210 so the cost is not too high.
I can take the single and drive the mid-drive on the left side for it to exit the 21T gear coming off the right. 700 RPM spinning a 21T going to a 44T NuVinci rear gear gives another 2.1:1 gear reduction to allow a 335 RPM input to the NuVinci hub. At the lowest ratio (0.5:1) this gives a max wheel speed of 167 RPM or 11.8 MPH. In overdrive 1.75:1 on the hub it calculates out to 41 MPH or a bit much. I can redo the gearing on the 16T motor side to run a 24T to bring the speed of the 21T mid drive gear down to 223 RPM to give it a gearing of 8 to 27.5 MPH. Running a 42T crank to the rear 16T freewheel would match the motor at 80RPM crank speed so all is well. The Stiletto frame helps this since the motor can be mounted near the mid-drive with the front crank position allowing for no leg interference when pedaling. It is a "crank forward" or "semi-recumbent" riding position or another added bonus.
The Giant Stiletto is black and everything on it is a plus for electric drive, from the riding position, the mid-drive for gearing options, steel heavy-duty construction, disc brake rear mounts, space for mega battery options, clearance for wide tires (it is stock with 3" wide tires) to the long chain guard. The only downer is the 1" fork bearings which limit suspension fork options. The $300 Schwinn OCC girder fork will match the style and has disc brake mounts on it...steel mounts for more durability. Once I pull the trigger on the fork, there is no going back. So I ponder the Stanton gear box and NuVinci hub concept. Since I'm running a mid-drive, I can always go with a derailluer setup for the rear, just gear down the mid drive some more with a 48T crank to get the RPMs in check. Use an 8-speed 13-32T rear cassette with my 26" 48-spoke mega MTB wheel. I can only run a 2" wide 26" rear tire but at least it would get me on the road and save serious cash to see if the drive works. That would put the bike in the 12.8 MPH to 31 MPH speed range I'm looking for. To align with the gear box 5:1 reduction and the mid-drive 3:1 reduction, I would have to run a 52T front pedal crank to the mid drive gear ratio but that is not a problem. So many options with the chopper.
I just get this feeling that I am missing something. $300 for the suspension springer fork and $170 for the gear box is "all in" for me on this project. That is in the X5 price class to get the project started.

Here is the link to the Stanton gear reduction boxes:

http://www.staton-inc.com/Results1.asp?Category=21&offset=90

Hope I am not digging myself a very expensive hole.... :x

 

[Comfortzone]

Did you do this project ? I had similar ideas using a bafang mid drive emotor but cant get any confirmation from anywhere that it would fit a bmx bb.
Everyone says the bafang will fit 99% of bikes. But it is made ONLY for standard BB.