Kepler
10 MW
So where do you go after a 12kW Stealth Bomber, custom Stealth Fighter, a weight weenie carbon super commuter? No secret I am a fan of Bafang mid-drives so it stands to reason this build would would be based on one of these. 
So this is what I came up with.
View attachment 3
The bike in its current configuration
Base bike is an XLframe Specialized 29er Camber. Front Shocks are the stock 120mm RockShox Recon Golds. Rear shock is a DNM air shock which replaced the stock Ario Rockshox item for some extra travel and a bit more plushness giving a total 120mm of travel back and front.
A BMX style headstem was fitted to tighten up the reach and the chain ring side of the bottom bottom bracket milled down 4mm to 68mm to improve the less ideal chainline typically encounter when fitting a Bafang mid-drive.
A Bafang 750W BBS02 mid drive was then fitted complete with a 961 display unit. This is such an easy part of build and takes very little time to install. The modern curved lower down tube found on most good quality mountain bikes is not so good for providing an ideal platform for this drive and forces the bulk of the drive unit to hang quite low. Luckily the Camber has great ground clearance and even with the low mounting position, there is still 10" of clearance. As a precaution, a bash plate was fitted to protect the drive from any front impacts and hopefully allow the bike to skip over any logs. So far this has worked out to be a very effective solution.
A custom 104mm BCD chain ring adapter was machined up and fitted with a 44 tooth chain ring replacing the stock 48mm item. Main reason for this was to clear the chain stay but also to give the bike a little more torque for hill climbing.
View attachment 8
Next the stock thumb throttle was removed and a push button throttle fitted together with a micro switch activated by the gear selector to cut throttle when shifting gears. This required a simple dual voltage divider circuit to deliver a full throttle signal with the button and approx 5% throttle with the micro switch.
Now to the battery set up. I quite like the simple front mount battery pack set up but wanted to do something a little different on this build. With the long down tube on this bike, it gave me the opportunity to design and install a long slim battery housing using 50mm square aluminium tube. I needed to fit the maximum amount of battery into this tube and found 3 x 5.8 ah 5s Zippy Compacts in a row to be an ideal fit. Battery cables were then brought up through the top via insulating grommets and series'd up across the top to make up a 15s 5.8ah pack providing 300Whr usable capacity. End caps were milled using machining plastic and an extruded aluminium cap milled down to size and fitted over the top of battery cables. The end caps are machined to match the frame tube profile and keeps the pack stable. A flat plate attached to the bottle cage blind nuts supports the bulk of the pack with the Velcro straps finishing off the mounting system. A permanently mounted volt meter was also fitted to keep an eye on charge level. So far just one of the batteries is monitored. This is mainly to keep things simple with the balance condition of the other packs checked manually on a regular basis
For this bike to have a dual role, a second set of road wheels we're build for on road duties. Road wheels use mountain bike hubs laced into 700c rims. 25mm Gator Skins were then fitted for road bike like rolling efficiency. With 2 sets of fully built wheels including discs, conversion from on road to off road duties take just a minute or two.
Other modifications include custom programming of the BBS02 to remove all speed limits and to customize the levels of PAS to my liking.
Weight was an important factor in this build but more important was that the bike needed to be fast (in bike terms), handle great, and most importantly, a really comfortable ride. In relation to weight, in road trim, the bike tips the scales at 19.5kg (43lb) and in off-road trim beefs up to 23kg (48lb)
On road, the bike can sustain 45kph on flat ground with 35kph to 40kph being easy to maintain sipping around 250W. Pushing the throttle button boosts the power to 750W which is perfect for a boost up a hill if you need to shake off a persistent lycra who insists on sitting 3" off your back wheel for a free tow. This happened to me this morning and got a little tedious. After sitting behind him at speeds between 30kph and 35kph, I rang my bell and overtook him to settle on my cruise speed of 35kph to 40kph. For the next 5km, the lycra stuck to me like glue dangerously drafting me. Enough was enough. Hit the boost button and took the bike to its top sustainable speed on flat ground of just over 50kph for a few km. That soon solved the drafting problem and i settled back to my nice economical cruise speed again.
Single track is where I am really loving this bike though and getting far more confident on the technical and fast flowing stuff. The bike handles great and has excellent stopping power with the Shimano XT Hydros gripping 203mm rotors front and back.
Only other addition is a dropper seatpost so I can quickly set seat height on the fly to suit the type of riding being done.
Over all, very happy with the bike and its dual configuration capabilities.
So this is what I came up with.
View attachment 3
The bike in its current configuration
Base bike is an XLframe Specialized 29er Camber. Front Shocks are the stock 120mm RockShox Recon Golds. Rear shock is a DNM air shock which replaced the stock Ario Rockshox item for some extra travel and a bit more plushness giving a total 120mm of travel back and front.
A BMX style headstem was fitted to tighten up the reach and the chain ring side of the bottom bottom bracket milled down 4mm to 68mm to improve the less ideal chainline typically encounter when fitting a Bafang mid-drive.
A Bafang 750W BBS02 mid drive was then fitted complete with a 961 display unit. This is such an easy part of build and takes very little time to install. The modern curved lower down tube found on most good quality mountain bikes is not so good for providing an ideal platform for this drive and forces the bulk of the drive unit to hang quite low. Luckily the Camber has great ground clearance and even with the low mounting position, there is still 10" of clearance. As a precaution, a bash plate was fitted to protect the drive from any front impacts and hopefully allow the bike to skip over any logs. So far this has worked out to be a very effective solution.
A custom 104mm BCD chain ring adapter was machined up and fitted with a 44 tooth chain ring replacing the stock 48mm item. Main reason for this was to clear the chain stay but also to give the bike a little more torque for hill climbing.
View attachment 8
Next the stock thumb throttle was removed and a push button throttle fitted together with a micro switch activated by the gear selector to cut throttle when shifting gears. This required a simple dual voltage divider circuit to deliver a full throttle signal with the button and approx 5% throttle with the micro switch.
Now to the battery set up. I quite like the simple front mount battery pack set up but wanted to do something a little different on this build. With the long down tube on this bike, it gave me the opportunity to design and install a long slim battery housing using 50mm square aluminium tube. I needed to fit the maximum amount of battery into this tube and found 3 x 5.8 ah 5s Zippy Compacts in a row to be an ideal fit. Battery cables were then brought up through the top via insulating grommets and series'd up across the top to make up a 15s 5.8ah pack providing 300Whr usable capacity. End caps were milled using machining plastic and an extruded aluminium cap milled down to size and fitted over the top of battery cables. The end caps are machined to match the frame tube profile and keeps the pack stable. A flat plate attached to the bottle cage blind nuts supports the bulk of the pack with the Velcro straps finishing off the mounting system. A permanently mounted volt meter was also fitted to keep an eye on charge level. So far just one of the batteries is monitored. This is mainly to keep things simple with the balance condition of the other packs checked manually on a regular basis
For this bike to have a dual role, a second set of road wheels we're build for on road duties. Road wheels use mountain bike hubs laced into 700c rims. 25mm Gator Skins were then fitted for road bike like rolling efficiency. With 2 sets of fully built wheels including discs, conversion from on road to off road duties take just a minute or two.
Other modifications include custom programming of the BBS02 to remove all speed limits and to customize the levels of PAS to my liking.
Weight was an important factor in this build but more important was that the bike needed to be fast (in bike terms), handle great, and most importantly, a really comfortable ride. In relation to weight, in road trim, the bike tips the scales at 19.5kg (43lb) and in off-road trim beefs up to 23kg (48lb)
On road, the bike can sustain 45kph on flat ground with 35kph to 40kph being easy to maintain sipping around 250W. Pushing the throttle button boosts the power to 750W which is perfect for a boost up a hill if you need to shake off a persistent lycra who insists on sitting 3" off your back wheel for a free tow. This happened to me this morning and got a little tedious. After sitting behind him at speeds between 30kph and 35kph, I rang my bell and overtook him to settle on my cruise speed of 35kph to 40kph. For the next 5km, the lycra stuck to me like glue dangerously drafting me. Enough was enough. Hit the boost button and took the bike to its top sustainable speed on flat ground of just over 50kph for a few km. That soon solved the drafting problem and i settled back to my nice economical cruise speed again.
Single track is where I am really loving this bike though and getting far more confident on the technical and fast flowing stuff. The bike handles great and has excellent stopping power with the Shimano XT Hydros gripping 203mm rotors front and back.
Only other addition is a dropper seatpost so I can quickly set seat height on the fly to suit the type of riding being done.
Over all, very happy with the bike and its dual configuration capabilities.
