Econo-Eco Rocket

[John in CR]

While my 2wd monster nears road testing stage, it's time to start hatching the next plan. Since my son shows no signs of coming down to participate, it's time to go solo on building my coast-to-coast cruiser. For the first time I'll give real consideration to weight, so I'm going to put my Trek AL hardtail frame from an early ebike to use. I need to climb a big mountain efficiently, so hub motors in wheel are out. I want to make it flexible for which motor I use, though it will probably be a hub motor, either the tapped winding Xlyte 409/4011 or Grubee 500W hub motor I have. I will ventilate the covers for cooler running and quite high power potential, especially at 144 volts.

For simplicity and weight and space savings I want things to multi-task. My novel plan to do that is to use a rear hub as a jackshaft and combining shaft for pedal and motor power. This will mount directly in the rear dropout of the Trek frame. The novel part is that this will be an extended frame similar to xtracycle, and axle of the jackshaft hub will be the swingarm's pivot, saving space and weight along with making chain stretch a non-issue. To me this solves all issues of chainlines, and gives me multiple gears for both the motor and pedal assist, all very simple and without a bunch of bike mechanic stuff with which I'm only vaguely familiar.

John

 

[John in CR]

I made progress today and hit a temporary snag with the silly thing that bike axles don't use a common standard fine thread size. The axles I have are 3/8" with 26tpi, but 24tpi is more common. I just next to pick up a thread tap for 26tpi.

Note that I changed the thread title. I like naming bikes, so this one will be the Econo-Eco Rocket. Econo due to cheapness as you'll see below. Eco b/c it's electric, and I'm using lots of recycled parts, even batteries. Rocket because this recumbent/semi-recumbent (undecided) is going to get 9kw with multiple gears. You're probably asking how I expect to run that power through a Grubee or Xlyte 4x series hub. The answer is by ventilating the hub, AND going to 140V .

I ditched the AL frame as a base, because the head tube angle is too steep for this bike. Instead I'm using this $5 frame I picked up a while back that has a nice slack head tube, since I plan to build with the chainstay parallel to the ground.
View attachment 1

Here's the rear hub I'm using that still had the price I paid of $2.07 at today's exchange rate. I also picked up a longer axle today for $1.18 to accomodate the swingarm bushings that will also function as the outside axle nuts for this combining jackshaft to be installed in the frame above's rear dropouts. Below is the plan for the sprocket layout on the jackshaft. I have a left side freewheel thread on adapter with bolt holes that I may or may not use on the motor input sprocket. I was thinking to use #25 chain on the motor input, since I have a few sizes for sprockets and chain already. The pedal input will be a standard threaded cassette. The output to the wheel will go to a Nexus3 in the rear wheel. Note that I will do a reduction on the motor side, and gear up the pedal side compared to the output sprocket/input at the wheel. That's so I can easily get the ability to pedal at low cadence at 50mph, and with the Nexus3 gear range and derailleur range of the pedal chain, still be able to assist at low speed up mountains.


This build is going to go pretty quick, because all I have to fabricate are a very simple straight swingarm, bushings for the pivot, and an extension of the upper frame for the seat and attachment of the dual rear shocks (also a recycled item). Tuning the gearing and testing the 2 motors for which is more efficient will probably take longer than the primary construction, but at least I get to ride in that phase and get you guys some video of going up and over the mountain nearby.

John

 

[amberwolf]

That jackshaft is about the same idea I have for the bolt-together cargobike.
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=16920
The difference is it looks like yours is also the swingarm pivot point, if I understand correctly, and mine will not have a rear suspension for this version.

I'll be curious to see how yours works out, as it might affect how I do mine.

 

[John in CR]

The difference is it looks like yours is also the swingarm pivot point.

Exactly. I was originally thinking of just using a hub as a pivot, but then I thought about how much easier a combining jackshaft will make all my stuff to do with chains. For some reason I can't get myself to like the idea of using the BB for that. I just don't like the idea of a motor powered chain running so close to my legs. I remember shoe laces and pants legs mixing with sprockets and chains, but that was with pedal power and no big deal. A few kw would be a different story.

I'll be curious to see how yours works out, as it might affect how I do mine.

I should have an answer fairly soon, but I see no reason why it won't. I actually have a couple of bushing that fit an axle, but they would just slide over the axle and ruin the threads over the long run. This way they will replace the nut, and the 2 piece bushing, both threaded, will act as a double nut.

Loctite, making the outer bushing also like a castle nut, and a cotter pin, I think are still called for despite the double nut action, since a swingarm falling off is an unacceptable high price failure. A driveshaft falling off a car may not pole vault a car, but a swingarm falling off of a bike surely would in just the wrong conditions.

I should end up with a bike capable of 50-60mph if I want to gear it so (faster if I go with a 3/4 fairing). It shoud be able to climb almost any pave road, and at 20-25mph should have a range of 50 miles using my last purchase from DrBass. The total cost should fall in the $700-800 range including hydraulic brakes, the Nexus3 and depending which controller I run. That includes over $100 just in shipping and taxes that I paid to get the stuff from Miami to here, and about half of the cost is the 1kwh+ in toolpack batteries. If I stay under 100v, then I can even us my Lyen 9fet, which was really cheap.

I'm pretty sure the drive train will prove out, which gives me a viable solution for lower power conversions for the locals, using the cheapest and smallest direct drive hubs I can find. In quantity, those are well under $100/ea including a controller. It's the mountains here that prevents a straight hub motor solution.

It will also make a good test bike for my ventilated Fusin geared hub, though I won't try to run so much power through it.

John

 

[John in CR]

So I'm pulling my hair out after my machine shop buddy tells me the supplier in Costa Rica has no carbide 24tpi taps, and has no 26tpi taps at all. WTF, so now I have to fabricate a hub from scratch because of one tiny piece. I go to the big LBS nearby with my fingers crossed for an easier solution. I tell the guy I'm looking for a 10mm axle with metric 1mm threads, but no. I start explaining what I'm doing, and the older guy overhears me, and goes rooting in the back, and comes back with a 14mm bike axle with sealed bearings what appear to be 1mm threads along with a pair of hubs the same.

Closer inspection of the hardware on the raw axle shows a threaded spacer on each to lock against the inner race that has a flat segment 6mm wide. I'm looking at it and can't believe it, because the spacers will work as my bushings. It also came with some nice long nuts that will be easy to secure to the axle How lucky is that, because the work to create my pivot is almost done for me except to drill a hole in the blade coming from the swingarm. I figured while it was my lucky day to ask if they had any old 3 speed freewheels, but no luck there. $18 later I'm out of there with more than I dreamed of going in. I got home and tried a file on the corner of that spacer and it's even made of a nice hard steel. It looks like all that's needed is a bit of polishing to turn it into a proper bushing.



John

 

[John in CR]

Since this combining shaft will enable an ultra wide gearing range, this will be my first ebike that I can actually pedal other than a bit of pedal assistance in the first 20-30ft when taking off from a stop. My goal is to be able to pedal assist fairly leisurely at 40mph+. This build will go together quickly now, so it's time to decide on gearing, but what is a leisurely cadence? Is a cadence of 40 reasonable for a quite leisurely pace, and then as I start getting into better shape I just go down a gear or 2 for more aerobic training? A cadence of 1 per 1 mph, sounds like a good goal for a high speed rocket.

John

 

[Skiv]

but what is a leisurely cadence?

It's individual. That'd be a little slow for me, and I'm traditionally a stoker instead of a spinner.

A 26-inch wheel with a big tire is going to make a little over 700 revolutions in a mile. 40 mph is roughly 466 revolutions per minute. If your cadence at 40 mph is 40 rpm, then you need about 12:1 gearing for your pedals. In simple gearing that's a 14-tooth rear and 168-tooth front chainring. I'm making a lot of assumptions here, and not showing my math, but I can if needed.

Edit: OK, I see the Nexus 3. 12:1 is doable, but at that tall a gear you won't be able to put much power through the pedals.

 

[amberwolf]

My goal is to be able to pedal assist fairly leisurely at 40mph+. This build will go together quickly now, so it's time to decide on gearing, but what is a leisurely cadence? Is a cadence of 40 reasonable for a quite leisurely pace, and then as I start getting into better shape I just go down a gear or 2 for more aerobic training?

I'm a wimp with a capital spaghetti noodle, but typically whether I'm on ebike or not, my cadence is 60-80 minimum, more like 90-100 if I am really pumping (which I don't do very often).

So Skiv is probably right about the gearing and such.

 

[John in CR]

Guys, "leisurely" is the key word. Right now my cadence is zero other than a handful of strokes when taking off from a stop. Top gear would be half for show, and half to do at least something with no excuse to not pedal. I'll have front and rear stacks on the pedal line, so with the almost 2:1 of the Nexus range available to me and the motor, I should be able to offer meaningful pedal assistance even up an extremely steep hill, despite the seemingly outrageously steep gearing at the top end. I'd rather shoot a bit high on the gearing than too short.

Also, my top gearing ratio probably limited to about 14:1 with standard components without even considering the overdrive 1.33:1 of 3rd gear on the Nexus. If it wasn't for the relatively large sprocket standard on the Nexus, then over 20:1 would be easy. You have to keep in mind that the output sprocket on the combining shaft will be chainring size. To be able to get away with that, I'll need to gear down the motor input to the combining shaft. The motor gearing is what I'll have to get dialed in properly before it's all said and done, but I sure have a lot more flexibility than having the hubmotor in wheel.

 

[recumpence]

John,

I love pedalling while the motor is running. I think it is great that you are looking in that direction. You will be surprised how much exercise you will get doing just that, not to mention added range.

Glad to see someone looking at actually participating with the bike, not letting the motor do all the work. I even like to pedal along with my really fast bikes.

Matt

 

[John in CR]

Matt,
Thanks but don't give me too much credit. My ebikes will always be pedal assist instead of electric assist. I've got a 20+ mile stretch of brand new highway that is generally downhill and almost always a significant tailwind. Can you imagine the look on drivers' faces when a fat guy pedaling a bike looking thing passes them as they're cruising down the highway? Now that's exercise that I call fun.
John

 

[dequinox]

I sort of aimed high when building my bike, but have adjusted the chainrings some since I first got it together. It was around what I figured was 100 per min...but now is down around 60 with proper gearing while moving 20mph. For those of you interested...or nay...obsessed with cadence, I found a little product by our friends at Garmin that might be of interest:

http://www.holabirdsports.com/m/Miscellaneous/Heart-Rate-Monitors/All/p1/052117.htm