The Gun Counter

Got the bug I do. 2 bikes into now. I can see a spot welder in my future for building up battery packs.

Got a used e-bike off Craigslist in August (350W 36V direct drive rear hub). A bit of a mismatch for my weight and our hilly area. Dear wife co-opted that one anyway Works well for her being 100# lighter and way more fit (she bike commutes 3 days to work, and out the door 2 days by 0500 for a spin class).

Converted my old MTB to an electric middrive (750W geared reduction motor integrated into the crank bottom bracket). Got it running last week and still haven't wiped the grin off my face. It's a sweet match for our hills and my weight. Immediately obvious I need to be upgrading brakes on mine.


There's all sorts of rabbit holes to go down on the interwebz. A lot of very interesting homebuilds out there. LINK

Lucky you! Have fun.

Acchhh... Dear wife's commuter is down for the count while I return this one and re-order a smaller pack. more fun with batteries...
The used bike I bought first had a battery of undetermined age and condition. So I pretty much just paid the price of the bike sans battery. Figured I'd run it till it died and then improve on the set up. It's a rear top rack mount in a cordura bag. Not an ideal setup for weight and balance. Would like to put the battery low and toward the center in the frame triangle. Well, it pooped out. 2 lights out on Battery Mgmt System (battery balancing board) gave a clue. It's what's called a "duct tape" unit so it was easy enough to cut into, get at the connectors and put a meter on it. Was hoping a couple cells were way out of balance and could be brought back with some charger tricks. No joy. Looks like a couple cells went toward zero. Probing 3.7, 3.7, 3.7 then nada, nada, back to 3.7, 3.7...

If I had more time and the tools I'd prefer to build a custom fit battery up in the old SLA battery case behind the seat tube (it's just a placeholder casing now for some of the old wiring and the motor control unit. A custom build is not going to happen at this point. So, I bought a bag that fits the triangle and a new duct tape 20Ah pack that should have fit. The Brown truck of happiness dropped that order off late yesterday.


Houston we have a problem. The product description was 220mm x 140mm (8.66" x 5.51").
It actually is 266.7mm x 146mm (10.5" x 5.75").
The triangles on these new fangled MTB-ish frames are pretty tight so that extra 46mm of length killed it for this triangle.

Got a smaller, spendier, probably better quality Samsung based pack coming in exchange for a about 10% more denaro. The guy pulled one from stock last night and measured it at 8" x 6". If the outline template I test fit is right that should work.

A few pix of my mid-drive install...

Out with the old, In with the new, Turn 'er over and get started on wiring up controller, speed sensor and mounting the battery. There she is with the battery in a bottle or "dolphin" pack install. Here's a look a the controls.
The LCD display lets you set things like wheel size, speed limiter, kmh vs mph. Inadequate battery feedback, just volts and instantaneous amp draw. That's not much help with Lithium Ion batteries. Voltage stays pretty level till right at the end when it drops off a cliff. Not much help with judging remaining capacity.
Need an amp hour readout. That's on the wish list. I'll be tempted to drop the big coin on a Cycle Analyst unit.

The brake controls were swapped out for units with microswitches that switches off the pedal assist when they are engaged.
To the left on the bars is an on/off;+/- assist level control pad.
To the right is a thumb throttle to override the cadence sensing pedal assist.

I know, I really don't have time for this sort of battery project and shouldn't be contemplating it but...

Here's a great thread with a guy stepping through a big triangle pack build out of 18650's.

Link

Dumb question, but with that new crank and motor set up, do the pedals move constantly, or is there some sort of clutch that lets you hold your feet still while the motor does the work.

One more that I may have missed in context: are you retrofitting a regular bike or an originally electric bike?

This looks really cool.

The crank freewheels if you don't pedal. You don't have to pedal constantly. The more you pedal and the lower your assist setting the less current you draw. You can take direct control by hitting the throttle... To infinity and beyond!!!

Basically senses cadence and then adds assist to help maintain the cadence depending on how much you are working. There are more advanced torque sensing systems (vs cadence sensing) out there.

Yep, this is a retrofit to my old bike. It's not been getting much use at all. Too hilly around here for a fat outta shape guy to just run off quick to the grocery (1 mile one way).

Every ride is a full committment to a training ride and a shower (and a push up the hill home). Now I pedal up the hill in first with only first level of assist at 8-10 mph and at pedaling between 60 - 80 rpm. Goldilocks solution for me-- just right.

By law to be street legal classified as a bike, no registration or license, it needs to be 750W max and max no-pedal speed of 20mph on flat road with a 170# rider.

Out in the flats I run up past 25mph pedaling with assist.
I could swap out rear cluster to an 11T high gear and get higher top pedal speed. Probably wouldn't be prudent at this time. First there's going to have to be a brake upgrade to disks.

Just saw this news. Looks like CA did something right in the ebike law that just was signed into law.

LINK, RTWT

So on a regular bike you can go as fast as you want, but if you have an electric assist, you have to limit your speed to 20mph or less.

Yay, government. You make so much sense sometimes.

Not quite. It's limited to either 20 or 28mph with no pedaling -- throttle only.

Pedal while running assist and you'll be more concerned about the limits of your brakes than the speed limit in throttle only mode. I see 30mph pedaling my MTB with 26" tires and a 42T chainring.

On a 26in rim with 52x11 gears, 100bpm gets you 36mph.

700mm tires with 52x11 gears and 80bpm gets you 30mph, 100 bpm get you 37mph, 120bpm gets you 45mph. With motor assist you can sustain higher gears longer and with more slope.