His and Hers ebikes on Cannondale mono-pivot frames.

[jag]

I had wanted a full suspension bike for some time. Now I'm riding a 72V, 9C Specialized Stumpjumper hardtail: http://endless-sphere.com/forums/viewtopic.php?f=4&t=9549 Riding the hardtail home at night I end up hitting potholes and bumps I don't see. The front shock goes smoothly over the bump, but then when the rear tire hits I'm almost thrown out of the saddle. A full suspension would help navigating both the urban jungle and trails. I was watching Kijiji and Bargainfinder for several months. The Stumpjumper was bought for $75 and fixed up with some sweat equity (particularly the stubborn Manitou fork)

Now I was ready to spring for something nicer. And one for the wife...

My first score was a 2004 Jekyll from a DH rider who wanted to upgrade to a more DH specific bike. At first I was suspicious about the Lefty front fork, but riding it about the trails here I've come to love the handling of the bike. It is known not to be a very pedal efficient design, but for electrification that matters less. The oversized alu tube frame is very stiff, so I hope handling should suffer less from the added battery weight than it did on the Stumpjumper frame (which by no means is a bad frame either, but flexier like other high quality CrMo frames.)

I looked long and hard if I could squeeze an RC motor into the triangular spot between the rear shock and BB. However it is very tight and I feared it would have me building all summer instead of riding. Instead I'll go for an easy install. Current plan is:

* BMC v3 + Controller (I'm keen to take up the challenge so many have tried to feed thicker wires though the axle. Maybe Luke's method with thin heat shrink, using a press to preshape the bundle before heat shrinking. This way the wire cross section will be pie-slice instead of round, so to maximize the amount of copper)

News: Apr 8 bought BMC v2s + 35A controller from shinyballs for the Jekyll above
ordered 2 Meanwell chargers from national surplus
Need to order cells and build 48v battery

News Apr 15
Ended up ordering two 31mm wide rims from niagara cycle to fit 2.35" big apple tires
1 x Sun Single Track Disc Rim 26" 32 Hole Black (55645) = $34.99
1 x Sun EQ31 26", 36h PV Disc Rim, 559 ISO, Black (415634) = $62.40
Also ordered Axiom Odyssey rear rack


* Likely A123 batteries. A pack of 15Ah prismatics fits nicely in the frame. The cardboard box is the same size as cell-man's 12s, 15Ah pack. I'll make an alu enclosure and some frame mounts.

* Left half twist throttle. I'm so used to left throttling now. Hoping ebikes.ca will get some in by the summer.


My second score was a used Cannondale Prophet. The geometry is perfect for my short wife. The frame design gives low stand over height despite the tall suspension. Now this one lends itself to an RC build. See next post. I'll be jealous of my wife...

You might ask why Cannondale aluminium frames? List rumour is that aluminium is not suitable for ebike building. Well, I have good experience with Cannondale frames, MTB, road and touring. They use relatively soft aluminium, compared to others, so hopefully cracking will be less of an issue. I also like the Cannondale engineering. We'll see how they hold up in a year of so.

 

[jag]

Recently I came across an ad for a used Cannondale Prohet at a good price. The mono-pivot suspension link goes a bit in front of the cranks, and I'm hoping to attach some brackets that allow me to mount a drive system. Goals are: Motor mounted on the swingarm to be able to have a fixed chain length and avoid chain tensioner arrangements. Yet put the main weight (motor) as close th the pivot point to give low inertia, and low unsprung weight. (a kg at the hub affects handling much more than a kg near the pivot)

This is a crude overlay I did on a picture. I'll have to do detailed measurements and a stress analysis (Maybe a good FEM project).

The green lines outline an aluminium bracket to be fixed (screwed, epoxied or welded -- don't know exactly what alu is in the casting of the swingarm. Suspect 6061). A similar bracket will be on the other (pedal chain) side. For a prototype I will just cut the bracked out of sufficiently thick alu sheet. What's your guess of sheet thickness? 6mm ok? 8mm?

Between the two brackets there is 3" of space to mount a motor. One early thought was a low rpm, high torque pancake motor . A Mars would fit, but at 9-10kg it is almost the weight of the bike (14.5kg). My current better idea is to use a good RC motor and a two stage reduction.

Here's where Matt's offerings come in: The light blue circle indicates a 3" diameter motor, such as the Astro 32xx series. The 3215 is the closest fit lengtwise in the brackets. A regular bike chain drives a 12 to 60 tooth reduction to the wheel. I want to try to mount a 60 tooth roadie sprocket on the disc brake mount points. Maybe I'll just screw it to a disc with a size matching the 130 diametre road standard mount points, or if that is to wiggly I'll make an alu adapter. Then have to think of another rear brake arrangement. (rim, regen or a second larger disk on the same adapter.)

The first reduction stage will be on the other side. There is 35mm of space between the far side mount bracket and the pedalling cranks. The three front chain rings intrude in some spots so exact layout has to be considered. Here a belt, chain or gear reduction could be mounted. An alternative would be the Currie planetary that Amberwolf posted. It almost exactly matches the OD of the Astro and adds just 21mm, but as discussed in previous threads might be noisy.

Martin

 

[Miles]

How about using #219 chain, rather than bike chain? It would get you a greater reduction in the same space...

 

[jag]

How about using #219 chain, rather than bike chain? It would get you a greater reduction in the same space...

I'm open to ideas.
I had picked bike chain because I thought I would need 2 stage anyway, bike stuff is available everywhere, and the bike components design (particularly the large 60t sprocket) blends a bit better with the bike.

 

[Miles]

12t to 60t only gives you 5:1............ Using #219 chain, 12t to 92t gives you 7.7:1.............. More compact first stage or greater overall reduction.

See also, David Schneider's build, here: http://spectrum.ieee.org/slideshow/geek-life/hands-on/an-ebike-potpourri

 

[jag]

12t to 60t only gives you 5:1............ Using #219 chain, 12t to 92t gives you 7.7:1.............. More compact first stage or greater overall reduction.

See also, David Schneider's build, here: http://spectrum.ieee.org/slideshow/geek-life/hands-on/an-ebike-potpourri

I saw your bike in there also. You've got a celebrity in your house (or garage)

I'm looking at a total of about 20:1 reduction. I had thought of splitting that somewhat evenly as 4:1 1st stage (will consider experiments with belt, chain or planetary) and 5:1 secondary, which is also the rear wheel drive chain. Is another split better?

Another option is of course higher torque motor and a single 8:1 or so stage. Not sure what motor to pick. An Astro 3220 would work, but is pricey. A larger diametre motor would be better. Used Mars can be inexpensive, but are heavy. I'm hoping to keep brackets, motor and any gearing at or below the 4kg range. Any suggestions for motors about 3" long but larger diam and higher torque than Astro?

 

[jag]

Here are some figures of what I was hoping to achieve with a 4 turn Astro 3215
The 5 turn is listed at 200 rpm/v, so the 4turn would be 4 turn 250 rpm/V right?

For starters I have a bunch of DeWalt 8s packs, so I can get 26V or 52V nominal packs. Plan to get some cellman packs later. Was thinking 26V for the wife and 52V when I get to try it out .


Motor rpm at no load, the standard -20%, and full loads interpolated (intelligently guessed) from some of the Astro application examples:

RPMs:
V Noload -20% full load Power
26 6500 5200 4500 (1.4kW)
52 13000 10000 8-9000 (6kW)

With a 20:1 reduction:
motor rpm wheel speed
26V 4500 - >250 -> 30km/h
53V 10,000 rpm - >500rpm -> 60km/h

Road speeds achievable:
26" tire 100rpm -> 12.3km/h
Rpm 100 300 500
km/h 12.300 36.900 61.500

So at 26V it would have decent eBike "street legal" performance, and at 52 V superbike. 52 might be pushing it though. I could also split a pack and go 12s to 40V.

 

[Miles]

20:1 seems fine but, if the second stage was only 5:1, it would mean (for belt) something like a 72t pulley or larger on the first stage - that's why I suggested using the #219 chain. Just a suggestion - either would work.

There's not that much choice in motors of the size to do a direct drive for a bike - it's a pity...

This is a bit too big and heavy, maybe? http://www.endless-sphere.com/forums/viewtopic.php?p=249609#p249609

 

[jag]

Moving the Prophet build thread to http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=17588

Cannondale Prophet belt drive with 5.6hp Astro 3220

 

[BLUESTREAK]

HEY JAG: PLEASE WATER THOSE 2 PLANTS,THAY LOOK SO SAD. :lol: :lol:

 

[jag]

HEY JAG: PLEASE WATER THOSE 2 PLANTS,THAY LOOK SO SAD. :lol: :lol:

How about painting the house? I'm obviously not keeping up with the Joneses on the street.