Introduction: Mountian Bike to Off Road E-Bike
Rocky Mountian ETS X-50 manufactured from around 2003-2008, they sold new for 3K+USD, and weigh around 26lbs (12kg)$
Conversion to Long Range Touring/Hard Core Commuting, Off-Road Capable Electric Bike, or GET OUT THERE AND HAVE A BLAST EXERCISE MACHINE!
A friend living in Victoria B.C. aka Bike nirvana, was commuting to work on an older bike, but finding that especially to keep up with road traffic safely, it was hard to get to work without being sweaty sometimes. He wanted to keep getting some exercise, he wanted to go a bit faster, and be less sweaty. As he thought more about it, he wondered about having some extra power to make longer trips easier. We talked.
I used to bike a lot, about 25 yrs ago, (bike courier, Calgary AB, 2 winters! back in 90's) so a few years ago when I saw this bike for sale I thought I’d get back into it, so I bought it, and didn’t. The bike sat, I moved with it to the Kootenay’s and largely it still sat (while trying again in the Kootenay's, I had an encounter with a bear and felt I almost couldn't outrun it, demotivating...).
When Ike mentioned he was interested in getting an E-Bike, I suggested upgrading the old Rocky Mountian ETS-50, and away we went. He’s now the proud owner of a long range touring/backroad monster that could allow him to do 200km/day.
An issue was that Ike really wanted a high capacity battery, which wouldn’t fit inside the frame of this bike, and which I didn’t feel good about mounting to the front/bottom of the down tube. So, as you see, I installed it on the top tube with riv-nuts, which I’ll detail later. This looks big, but we’ve found it doesn’t impact the bike handling much. You can see me bunny hopping it in the youtube video.
We installed a Bafang 750W BBS02B Mid Mount motor and the 48V 16.5Ah LiIon Battery, going from about 12.7kg (26+ lbs, not super light to start with) to + 8.5 kg motor + 4.3kg battery = 25.5kg (55lbs).
It’s a great ride, amazing power and RANGE! and the up top battery actually feels a bit like a dirt bike gas tank allowing for positive knee placement position.
A 1hr trip at 30km/hr uses about 4.5 Ah, with stiff pedalling, so it's range is easily over 100km.
Mountian Bike - 2003-ish Rocky Mountian ETSX-50
Bafang BBS02B Mid Mount Motor - from Golden Motor - about 900 with shift sensor, display, install tool
48V - 16.5Ah LiIon Battery - from Ebikes.ca
Battery Charger - Programable charger to allow for charging to less than full capacity for extended life - from Ebikes.ca
Double Bob battery mounting plate - from Ebikes.ca
From the hardware store
RivNuts - these are very cool fasteners that allow you to put a threaded insert into a hole in sheet metal or thin tube, and have it expand to lock itself in place. When it's done properly it makes for a very strong a long lasting connection. I'm calling them RivNuts, but they are available under different trade names.
Threaded rod- the same size as the threads on the RivNuts you use as it's going to be the tool for compressing the RivNut
Coupling Nut - these nuts are super long so they can join two threaded rods, get one the same size as the threaded rod. This is what you are going to spin on the rod to squeeze the RivNut into place.
Washers - to fit threaded rod
Epoxy Putty - This stuff is very useful! It's a two part epoxy paste, or play dough mixed with aluminum filings. It's one part on the inside of the role, and the second part is the outside. You just cut off what you need from the roll, unwrap the plastic wrap, and squish it lots.
Step 1: Installing the Battery
This was the difficult issue in this project, how to install a 6+ kg (16.5Ah 48V) LiIon battery to a fairly thin wall aluminum bike frame.
The large battery was chosen because Ike wanted both very long battery lifetime, and the ability to take long trips occasionally, and was willing to accept that it might not longer be as capable as an off road bike.
The outcome is that a 1hr trip at 30km/hr uses about 4.5 Ah, (just over 25%) with stiff pedalling, so it's range is over 100km, even at a good clip.
For the first test to get a sense of what it would feel like with a battery up there, we taped stryofoam blocks to both sides of the frame, to make a flat top platform for the battery to sit on. I worked well, but the foam was a bit squeaky.
So I 3D printed a mount to see what a bit harder riding would feel like. It's the pink and yellow assembly under the battery in some of the photos.
It felt great, not a lot of standover height with feet on the ground, but pedalling it wasn't noticeable, and on downhills, when you are standing on the pedals, it gives a nice position for your knee's to lock you to the bike.
Once we were happy with the general position, then I started thinking more about the final mount. I thought about building my own mounting plate, but curving it to match the top tube seemed like a big challenge. The solution was the "Double Bob" battery mounting plate from Ebikes.ca at 25$!
This plate has a number of drilled holes to mount the plate to the bike, via water bottle mounts, or rivets, and has relief slots cut so that hose clamps can be added, making for a very strong install, and making temporary mounting very easy.
An issue was that the cables and brackets routed along the top tube were in the way. Good news is that of the 3 cables routed here, one is front derailer, which we don’t need any more with the Bafang mid mount motor, one is brake line, which can be repositioned and doesn’t need the bracket, and the last one is rear derailer, which I can run in a housing from the handlebar shifter to the rear chainstay, so I removed the bracket by carefully cutting the weld (and not the tube). I found this pretty stressful, I'm a pretty experienced metal worker, but have never cut or drilled a fancy bike.
I used the Double BOB mounting plate but had to make a few minor alterations to it as the top tube of the bike isn't completely flat, it changes angle right at the end of where I wanted the plate to mount, making the plate sit up at one end. So I filed and sanded the end of the Bob plate to fit.
Once I liked the fit, I used the hose clamps to temporarily mount it, and tested the battery plate and battery fit. After being assured of good fit between the plate and the frame and that the battery was still able to be slid forward for removal, I removed the battery and battery plate. With the Bob plate mounted via the hose clamps, I drilled the 5 holes in the bike frame, using the Bob plate as a guide.
I removed the hose clamps and Bob plate, and then put the Bob plate in a vise with a scrap piece of aluminum that I will use for installing the RivNuts. I use the same bit and drill use the Bob again to make a set of matching holes in the scrap plate.
Then changing drill bits up to the smallest bit I can just barely get a RivNut to slide into. It's best practice to have a very clean tight fitting hole for RivNuts and pop rivets, as an enlarged hole, or a hole with burs or debris from the drill bit can have a big impact on joint strength. I drilled the bike frame holes out larger with the new bit, and then carefully deburred the holes by scraping with a small sharp cornered file.
I slid a RivNut into each hole, and set the scrap plate with matching holes on top. I put bolts into the 4 of the 5 holes and threaded them into the RivNuts. In the last hole I used a 12" long piece of high strength threaded rod 0.25" diameter, with a 90deg bend at the top. Before I threaded in this rod to the last open hole, I spun on a long coupling nut, and below that placed 3 flat washers. I lubricated the threads of the rod where the coupling nut was going to sit with a bit of grease, and tried not to get any on the rod where it was going to thread into the RivNut. I greased the washers as well, and then threaded the rod into the RivNut. After spinning and hand tightening the coupling nut down against the flat washers that now sit on the scrap plate I am almost ready to start cranking on the coupling nut to pull up on the threaded insert and crush into place. The last thing I do before this is to make sure that the RivNut is pushed hard into it's hole with it's flange tight against the bike tube. If the rivet is expanded without the flange being tight against the tube, it can be significantly weakened. So I used a clamp to push the scrap plate against the bike tube, holding the rivet in place. Ready to start placing the first rivet, the problem is that as you spin the coupling nut, even though it's greased, the threaded rod will want to spin as well, backing out of the hole. The solution is to hold the bend at the top of the threaded rod, with pliers or something (or make it long enough to hold on it's own). Now as you spin the nut with the wrench and hold the rod, the rivet crushes into place making a very durable connection. After repeating on the other 4 holes, I mounted the Bob plate and found that the flanges on the set RivNuts kept the Bob from sitting down on the tube. I put some tape on the bike frame to protect it, and took a file and removed a tiny amount of material from sides of the RivNut flanges, and had a perfect fit. As I was planing on large counter sunk machine screws for the new 0.25" threaded holes in the bike, I took the counter sink to the Bob plate and deepened the holes until my chosen screws fit flush. After trial fitting all that, I removed it again and added some metal filled kneadable epoxy paste. This two part epoxy comes as something a bit stiffer than tooth paste, usually as a little roll or log about 1" around and 6-8" long, with the inside being one part of the epoxy and the outside being another. If you do a good job of kneading it up, it sets up as hard as aluminum. It's quite stiff at first and I find rolling it long then twisting it and folding it, then repeating, gives a good mix in a few minutes. Wear gloves, epoxy isn't something you want on your skin more than you need. A small amount on the inside of the plate, especially at the Bob plate ends, and around the screw holes, means that the mount should be pretty well attached. Then I put it on, gently screw down the screws and clean up the extra epoxy paste. After 30 minutes the epoxy paste is set and the screws can be removed, and I used Locktite Blue thread locker as I reinstalled them and tightened them up firmly.
I only really needed the 3 threaded holes for the Bob Plate, however the two extra holes are available right through the Bob plate, so if I want I could add another 2 x 0.25" screws going from the battery plate, through the Bob plate, and into the frame. At this time I haven't, but you can see in the photo they are accessible.
Participated in the
Exercise Speed Challenge