Intro: Convert a Full-suspension MTB in to a Go-anywhere Ebike
Mountain bikes are great fun. Full-suspension mountain bikes are even better fun. Full suspension mountain bikes with a 1700W mid-drive electric motor and a 40-mile range are amazing. Let's make one.
We're going to be using the BBSHD motor system from Bafang. This fella will provide up to 1700W at 58V
Step 1: Stuff You're Going to Need
This is by no means exhaustive but is fairly comprehensive.
- Bafang BBSHD Mid-Drive motor system
- A suitable bicycle
- 70 x Samsung 30Q 18650 batteries (I recommend buying at least 75 as you are bound to destroy a couple)
- 0.15mm Nickel welding strip
- Paper battery insulators
- (optional) BBS gear sensor
- (optional) Hydraulic brake lockouts
- 12AWG power cable (about 4M of black and 4M of red)
- Suitable BMS (I used a JBD-HP14SA)
- 2mm acrylic sheet
- 3mm ply wood
- 1" x 2" wooden batten
- Two pairs of XT90SA connectors
- Various screws
- (optional) Turnigy power meter
- (optional) LunaCycle 60A power switch
- 60V 5A adjustable PSU
- Speakon 2-pole connectors (M and F pair)
- Cable ties
- Cable wrap
- Heat-shrink tubing (4mm for wires and 250mm ish for battery)
- 2.5" bathroom drain-pipe
- Bicycle stand
- Battery spot-welder
- BBSHD tool
- Hex wrenches
- Wire cutters
- Good 60W+ temperature controlled soldering iron
- Heat gun (or hair dryer + kitchen toaster)
- Wood saws
- Acrylic saws
- Gorilla glue
Step 2: Measure Your Bottom Bracket and Check What Type Is It.
The first thing we need to do is to make sure that our bike frame can take the BBSHD.
There are many different types of bottom bracket on MTBs but the BBSHD is designed for a standard BSA threaded item. It comes in 3 different lengths depending on the width of your bottom bracket; 68mm, 100mm, and 120mm. The 68mm item is good for bottom brackets up to 73mm in width.
If you don't have a standard BSA threaded bottom bracket then there is hope. This excellent blog post over at Empowered Cycles goes though bottom bracket types and the BBSHD in much more detail than is required for the purposes of this post.
Measure across the bottom bracket of the bike and see how wide it is. You can see from the picture above that this frame has a 68mm item. We're good to go.
Step 3: More Measuring and Potential Issues.
The BBSHD has a large secondary reduction gear housing that is 136mm in diameter. We need to make sure that there is enough clearance between the bottom bracket and the chainstays to accommodate this.
The first image here illustrates the reduction gear on a bike with a very wide chainstay but a narrow bottom bracket. The second image illustrates where you should measure to ensure a proper fit.
In the example bike, the BBSHD will not fit flush against the bottom bracket without fouling the chainstay. On a hard tail bike this is not so much of an issue as we can just use a couple of spacers and have it butted up against the frame. On a full-suspension bike this is a big issue as we need clearance for the chainstays to be able to move.
If you have wide chainstays but a narrow bottom bracket you have a few options which each have a few tradeoffs.
1 - Buy a larger BBSHD and use spacers - On the face of it this seems like the best option but with the crank gear being further out from the frame you may find that your chainline is unacceptable, preventing the use of several of your gears.
2 - Adjust your frame with an angle grinder - This can be an option if you only need <1mm of additional clearance. Check your frame thickness before you do this as you can easily take off too much and destroy the frame.
3 - Sell your frame and buy one that is more suitable - This is the best option as both of the previous options have tradeoffs that may make your unhappy with the final product. The third picture above shows the frame I used for my build (2009 Felt Compulsion 2) that has plenty of clearance.
Step 4: Batteries and Voltage
The BBSHD is designed to run at 48V and with a battery system of this voltage it will provide up to 1000W. However, the motor and controller are very over-engineered when compared to the BBS01/02 items and are more than happy at 52V or higher. For the purpose of this build we're going to go with 52V.
Most eBike batteries are made up of 18650 Li-Ion cells in various configurations of parallel or series. They are 3.7V nominal (4.2V fully charged).
We could buy an off-the-shelf battery for our eBike and that would be the simplest option. However, this is Instructables so we're going to build one.
First, a little battery instruction.
We can connect our cells either in series (+ve to -ve) or parallel (+ve to +ve, -ve to -ve). Series gives us voltage as the sum of the cell voltage. Parallel gets up capacity and current.
To get our 52V we need 14 cells in series (3.7V x 14 = 51.8V). We could make a simple battery with 14 cells but this would not be able to provide enough power to drive our motor. Each cell has a current rating. For series connections the entire battery will be capable of the maximum current of a single cell. We're going to use Samsung 30Q cells which are 3000mAh items and good for 20A. Our 14 cell battery would only be capable of a maximum of 20A and would have a capacity of 3000mAh - Not enough to go any meaningful distance and not enough current to drive the BBSHD at its maximum of 30A.
We want a good range for this battery so we're going to use either 4 or 5 cells in parallel to give us a current and capacity of either 80A/12000mAh or 100A/15000mAh respectively.
Step 5: Measure the Space for Your Battery
Lay your bike frame down on a piece of card and draw around the triangle. You can then either draw around each of the cells to see where the fit, or measure the template and create it in a CAD program. I went with the CAD option so I could play around with the positioning of the cells.
You can see from the CAD drawing that we can easily fit 70 cells inside our triangle. This will give us the 14S/5P configuration for 52V. 100A, 15,000mAh.
Step 6: Make a Jig for Your Battery Box
Cut out the template you made before by drawing around the inside of your frame triangle, and lay it on some MDF or ply-wood board.
Take some 1" x 2" pine or similar and cut it down and screw it to the board around your template. This will form a jig to make the perimeter of your battery box.
Step 7: Build Your Box Perimiter
The perimeter of the box is going to be made from acrylic. This is hear-wearing and easy to work with.
Cut some acrylic in to a long strip of width that equals your 18650 cells + about 6mm. 18650s are 65mm long (hence the 650 part of the name). We need some space either end for connections and for the thickness of our side-panels.
We want some nice curves for the corners of the box as sharp edges could be dangerous when riding. To form the curves we're going to use some 2.5" bathroom drain-pipe.
Take a heat gun (or if you don't have one, a household toaster) and heat your acrylic until it is pliable in the area you want the bend. Once pliable quickly place it in the jig and create the bend using the pipe. Repeat for the other two corners.
Once all the corners are made, cut off the excess and glue it with Gorilla glue.
Step 8: Add a Side to Your Box and Start Arranging Cells
Once your have the perimeter of your box, lay it down on some 3mm ply-wood, or some more acrylic and draw around the inside of it. Cut it out and attach it to the perimeter to create a side. I used ply-wood for my build for strength and then some acrylic over the top of it to make it look nice. I also added some small wooden blocks to add strength to the box.
The connector you can see at the front of the box is a Speakon connector. This is going to be used as the charging port. I used this type of connector because it's capable of dealing with about 15A (way more than I'm going to be charging at), they are very durable, and you can get waterproof covers for them.
Step 9: Prepare Your Battery Cells
Once you have the side on you can start arranging cells. I packed my 70 cells in as above. You can see that they are in groups of 5 (for the parallel connections) and alternate groups are arrange in the opposite direction to its neighbors to create the series connection.
The item with the wires at the bottom is the Battery Management System. You will need one of these to keep your cells balanced and healthy. I used a JBD-HP14SA which is capable of 40A and 14S.
Step 10: Buy or Build a Spot Welder
For this part you are going to need a spot welder. Don't even think about trying to solder the cells or you will destroy them.
You can buy basic spot welders on eBay relatively inexpensive. I chose to make my own following this design by darkkevind on YouTube:
I made a few modifications along the way to make it a bit more reliable but the basic idea is the same. Here's the Instructable for that build: https://www.instructables.com/id/Simple-Battery-Spot-Welder
Step 11: Start Welding Your Cells
Gradually weld your cells together in parallel groups. You can see that I managed to mess up some of the welds and had to cut a few cells out to replace them. You may find it helpful to make a simple jig for the first group of cells to keep them steady while you do the first welds. Remember to use some card insulators around the positive terminals.
Use hot-glue to solidly attach each group of cells together as you go.
Check the voltage as you go to make sure you have them welded correctly. For each group your pack should increase in voltage by 3.65V (which is the storage voltage that your cells will have come from the factory at).
A few of points to remember during this step:
- You are messing with a battery of 52V and 100A. This can do some serious damage so be careful.
- Wear eye protection. Hot sparks will mess you up.
- Test each cell before you weld it in. You don't want to have a bad cell in the middle of your pack.
Step 12: Solder Your BMS In
Once you have your pack together you need to connect the sensing wires of your battery management system (BMS). The BMS will monitor the voltage of your individual battery groups and ensure that the pack is balanced.
Most BMS will come with the wiring diagram printed on the side. I've annotated the Chinese annotated wiring diagram for you.
Step 13: First Charge
Once you have your pack together and your BMS wired in, it's time for the first charge.
I cannot stress enough: CHECK AND RE-CHECK YOUR CONNECTIONS
Set your power supply to 58.8V and 2A and switch it in.
And I'm going to stress this too: DO NOT WALK OFF AND LEAVE YOUR BATTERY CHARGING
A Li-Ion cell fire is no joke. Sit and watch your battery as it charges and be ready to kill the power if anything untoward starts happening. Watch your battery terminals for any signs of fluid leakage that you may have missed while welding.
If a cell explodes or catches fire, get far away from it as the gasses released are highly toxic.
Step 14: Wrap Up Your Battery
Once the battery is built, tested, and charged it's time to wrap it up. Take your heat-shrink wrap and heat it with a heat-gun (or hair-dryer) until it's tightly wrapped.
As a rule of thumb you want wrap that's 25% larger than your pack.
Check the pack fits inside your battery box.
You can see from the second picture that I have added some Velcro battery straps to the top of the box. This is for additional security inside the triangle.
Step 15: Attach the BBSHD to Your Bike
We now have a battery but we need something for it to power. Let's attach the motor to the frame.
Slide the motor through the bottom bracket, add the included bracing, and tighten up the securing nut and lock ring.
The BBSHD doesn't come with the tool to fit the nuts and I highly recommend that you buy one. They are relatively inexpensive and will enable you to securely fit the motor.
I recommend fitting the chain at this point to check your chainline. With my build I could immediately see that the chain was too far out, meaning that I would not have the use of the largest rear cog. To counter this I took 2mm off the bottom bracket with an angle grinder and used a front derailleur mech as a chain guide.
Step 16: Attach the Battery Box and Start Routing Wires
It's a good idea to start routing wires before you put your battery in the box. You may also find (as I did) that you can't actually attach the box with the battery installed due to clearance issues.
The item hanging out of the box in the first picture is a LunaCycle solid-state switch. This is an optional item as the BBSHD has its own power switch but I just felt better about having the ability to completely isolate the battery from the motor without having to pull connectors apart.
You can also see from this picture that I have flipped the shock upside down. This gives more clearance for adding air and getting to the damping controls.
Step 17: Adding Battery Battery Monitoring
The BBSHD's display isn't particularly accurate with it's monitoring of current and voltage so I wanted to add a secondary display.
Turnigy make an excellent little power meter that is very inexpensive. I bought one and added it to the stem of the bike using some nylon block. This part is completely optional and does actually complicate things due to having to route wires up from the battery and then back down to the motor.
You can see from the final picture here the arrangement of the controls for the BBSHD. I have annotated the picture, pointing out the major items.
Step 18: Fit Your Battery
I recommend laying your bike down on its side for this step as the battery is heavy and dropping it could destroy it. Once installed you can solder the power connectors and the BMS in. You can see that I'm using XT90AS connectors for the main power wires. These are good for 90A and the AS version is anti-spark. This makes connecting things together a lot less scary.
It's now time to start fitting connectors together and routing wires.
Step 19: Brake Cutouts
These are optional but I highly recommend that you fit them. They will kill the motor when your pull a brake lever.
The BBSHD comes with levers that are for cable operated brakes. However, as you are building a 1700W monster you are using hydraulic disk brakes (please use good brakes, seriously).
You can buy hydraulic sensors that are plug and play and consist of a hall-effect sensor, and a magnet. Attach the sensor to the brake lever housing and then find where the optimum position for the magnet is on your levers by holding it in position and seeing when the display indicates that the brakes are engaged.
I drilled a small hole in the levers to bolt the magnet in place but you can also use epoxy or similar.
Step 20: Speed Sensor and Gear Sensor
The speed sensor consists of a small magnet that you attach to your spokes and a sensor. This can be placed on either the front or rear wheels but I suggest the rear for ease of cable routing.
The gear sensor is an optional item but another that I highly recommend. It detects when you are shifting gears and drops power to the motor momentarily to ease the shift. You fit the gear sensor over the rear derailleur cable.
Here's a video of it shifting. Listen for the power drop.
Step 21: Tidy Up Your Cables
Tidy cables don't only look good, they also mean things are less likely to snag or work loose. I use standard spiral sheathing that can be bought very inexpensively.
Step 22: Admire Your Work and Go for a Ride
You should now have a powerful eBike that you have intimate knowledge of that has better performance than most of the pre-built bikes on the market.