25 December 2016

Lightning Rods Big Block Mid Drive - 2017 Configuration

The bike is built around the Big Block mid drive, made famous by Michael Backus (www.lightningrodev.com).  I purchased one of the earlier production Big Block motors back in 2015 so it was a little finicky and required a fair amount of back and forth with Mike to get it on the bike.  In the end (i.e. 2017) it just made more sense to send the whole frame to Mike and have him install it for me. This provided the added benefit that since 2015 he has continued to evolve his kit and sending the original back to him provided the opportunity to swap in all the various upgrades. 

At Mike's suggestion some of these upgrades included moving the 18t Drive Pulley out and replacing it with a 25t.  The intent here was to make things a little quieter and less prone to slippage.  The trade off is that, according to LR, I'm limited to a terrifying 60mph when in off-road mode (72V and 40A).  Note that when on public roads I always adhere to 182.1 of the BC Motor Vehicle Act.

Additionally, and as per Mike's repeated comments on the forums, he bolted a piece of aluminum between the frame and the motor casing to keep the twisting forces to a minimum. 

I had a couple of legit choices for the donor frame.  

Initially I had thought that I would use a an extra-large 2007 Giant Anthem 0 that I picked up off of Craigslist here in Vancouver for about $800.  This would allow for a ridiculous amount of triangle space and it was a good fit for my lanky 6'2" body type.  

As chance would have it I had also come across a large 2004 2004 Giant DH Comp on E-S which was available for $500.  I purchased the DH Comp with the intent of switching direction and mounting the Big Block on it instead

In the end, after lengthy discussions with Mike and flip flopping back and forth several times, I settled on using the DH Comp.  Despite the frame being a touch small (the spec from Giant's Japanese language web page reads that the the max 'suitable/appropriate' rider height for a large DH Comp is 185cm), Mike's repeatedly stated view was the the '04 DH Comp is nearly the perfect frame to use as a platform for his big block. Who am I to ignore.

Drive Train
The decision making around the drive train was convoluted, to say the least. I initially planned on using a Rohloff Speedhub because of its reputation for durability.

The Rohloff evolved into a single speed after a long conversation with Mike.  His argument, essentially, was that when a big block motor is driven by 72 volts (nominal) and 40 amps it dramatically reduces the need for multiple gears.  More specifically, the thinking is that if you don't have to climb lot of hills, and don't care about pedaling along, the use of a 72 volt battery to some extent takes the place of additional gears. This was the operating theory throughout much of the build process.  

In the end, however, I made a last minute / arbitrary decision to switch to an eight speed cassette with an 11-40T spread. This decision was driven by a combination of wanting to be able to pedal up a hill if absolutely necessary and advice around chain growth on FS ebikes that I got from my LBS and that was confirmed by Mike. 

LiGo batteries from Grin (www.ebikes.ca) are completely modular and come in 10S1P units (36V/10A/2.7Ah).  This is the battery style I've been waiting for.  8 packs, configured as "2S4P", yields 72V/40A/10.8Ah.  By following Justin's advice and charging to 80% and  discharging to 20% I'm hoping to stretch the LiGo's life out to 600 charge/discharge cycles over a 3 year period.  I have a pair of 72V Satiator's that I use to charge on each side of my commute (at the office and at home). 

The controller is an 18 Fet Lyen and will comfortably run up to 65A continuous (www.lyen.com) which allows for additional LiGo’s to be added in the future if/when I feel the need for more power. I asked the Ed to install an on/off switch right on the controller itself in order to reduce the likely hood of issues further down the road and to further comply with the applicable section of BC MVA 182.1.  

Battery Bag
Since I couldn't really fit enough battery in the triangle to make the round trip from home to my office I opted to just throw the battery into my existing commuter backpack.
E-bike specific items
Other e-bike specific items include a Cycle Analyst, a GPS enabled analogger and a Cycle Lumenator (www.ebikes.ca).  

A Cycle Analyst V3 ties everything together.

Non e-bike specific items
Other non e-bike specific items include 203mm discs.