The repairs on frame #2 are in progress, the gravel thing I was working on has gone on the back burner, and the Freeflow Technologies motor system has arrived. It’s time to build a downcountry e-hardtail!
Design goals for this are to keep the riding characteristics of my acoustic hardtail (fast, composed, balanced, playful). Some tweaks have been necessitated by the motor size (longer chainstays) and dynamics of riding a powered bike (keeping the front wheel on the ground under power). I’d love to aim for a 16kg (36lb) AUW but, given budgetary constraints, I think it’ll be closer to 18kg (40lb). Still pretty respectable for an e-bike and a heck of a lot easier to lift over a gate than my current Giant eMTB.
Tubing will be cromoly steel, probably plain gauge subject to what Ceeway can supply me, except the seat tube which has already been sourced from FBS following recommendations from the previous build. Dropouts are Metal Guru UDH cast steel. Motor shell supplied by Freeflow. Drivetrain is SRAM GX Transmission. Forks are RS Revelation 27.5" 150mm travel.
Freeflow don’t publish their prices publicly that I know of so I won’t do so here either, but prices did seem reasonable to me and they were happy to speak to me as a hobby builder, which differs from other major players. They’re very friendly and easy to deal with too, although I did find there were short delays in responding sometimes. Being a small company, I imagine there’s a lot going on so don’t be afraid to nudge them if they don’t get back to you in a reasonable time.
In case anyone’s interested, here are some photos of the system as delivered. They offer motor shells in steel and aluminium for custom builders but also publish full design docs on purchase to enable builders in other material or people who want to make their own motor interface. They don’t supply a dummy motor to mount the shell in a frame jig so one of these will need to be built. My dummy motor is in progress and I’ll publish designs here when complete.
The system is designed around a 53mm chainline and has a 5-arm 110mm BCD chainring mount. I’ve bought a 36T Hope Retainer ring for it which claims SRAM Transmission compatibility. I’m going to try it with the default 53mm chainline as that’s within SRAM’s published specs but have the option of fitting chainring spacers if needed.
I’m really into in FreeFlow and your design looks a lot like what I had in mind for my first one. I’ll be watching with great interest, best of luck with the build.
I’ve reached out and had positive responses from them which is refreshing as a small scale guy. I actually feel bad I haven’t had the time I’d like to get stuck into sorting out my own design. But following a quick n dirty copy/ paste into our current designs it looks like integration would be about as simple as it can get (not necessarily actually simple).
Thanks. I’ve been following you on Instagram for a while and really like your bikes. We definitely come from the same school of MTB design.
Aside from going a bit more over-sized with the tubing selection on this one, the other noticeable difference was needing to extend the chainstays due to the motor shell diameter. My previous build had 415mm stays but that wouldn’t work here so I’ve gone for 428mm which is about as short as I think I can go and still keep sensible tyre clearance. I’m hoping they’ll still be short enough to keep it feeling lively but not so short that the front end floats up when climbing under power. I ordered a second motor shell for a good reason
For 29" wheels, the stays would need to be up around 435-440mm so, theoretically, you can build it into your Eponym without making any geometry changes. From what I’ve read, the demo MTB which Freeflow uses is a Specialized Hardrock which had the BB removed and an alu shell welded in. If you’ve got an old Eponym frame kicking around, that’s probably your fastest route to a working bike.
DT goes up to 44mm from 40mm - supplier didn’t have suitable stock of the former. CS goes down a tube size to 19mm - I wasn’t happy with the way the 22mm tubes would interface with the dropouts - and up to 433mm length from 428mm to make sure I’ve got enough room for the tyres. ST gets a little shorter to make room for a 240mm dropper.
Since mitring the front triangle I’ve discovered that my jig’s wooden backboard has distorted under the weight of all the metal stuck to it so I’m going to be getting a metal welding fixture table next week. That’ll need assembling then I’ll check/adjust my mitres and weld the front triangle.
Final chainstay designs are still in progress but I’ve got a clear path to completion, then it’s on to bending. I still haven’t figured out how I’ll fixture them as that was the area which went least well with the last build.
I’ll be welding the tubes to the surface of the cabinet with this build although the cabinet will be drilled for drainage and cable access. Someone else (or maybe you somewhere else?) mentioned drilling to allow the tubes to pass through - apparently it helps avoid misalignment. It sounds like it could be a good idea so I may do that next time, especially if the ‘welding to surface’ approach causes me any problems this time.
Freeflow have .step models for most of the system’s components. They dropped straight into Fusion for me. You can see their motor/cranks, shell and external battery models in one of the renders in my first post.
A bit disappointing that Freeflow stopped trading earlier this year. However, with the system in-hand and the frame build under way, I’ll finish the build and ride the bike anyway.
I had a few setbacks earlier in the year including realising that my original wooden jig frame was distorted, which significantly delayed progress, but I’m back on track now. The build is pretty much done with only the rear brake mount and a little finishing work to be done before it goes to paint. Here are some progress shots for your viewing pleasure.
The charging port bridge. This was formed from 0.9mm steel sheet over a 3D-printed buck. I took 2 tries at this and the second one came out really nicely. After the bridge was welded to the seat and down tubes, I cleaned-up the excess internal metal to smooth in order to avoid damaging the cables which will pass through it before welding to the motor mount.
Chainstays with UDH dropouts, cutout for disc rotors, internal routing for wheel rotation sensor and 5mm plate on drive-side for tyre/chainring clearance. Check out the new chain/seat stay fixture system
I haven’t ridden it far - just up and down the terrace - but it was the first time testing the geometry and the motor system. First impressions are that the motor gives the amount of assistance I was hoping for but it’s quite noisy. I’d imagine this could partly have been resolved by software updates but that won’t be happening now so I’ll have to live with it. The SRAM GX Transmission system seems to fit the Metal Guru UDH dropouts just fine and was easy to set up.
Finished frame weight (unpainted) is 3.65kg. Fully assembled as seen here (not all components are final) is 19.6kg (43.2lb) which I’m very happy with - a lot more pick-up-able than most full-fat eMTBs I’ve handled.
… and now we wait for my Incepi brake mount fixture to arrive from Canada so I can finish this.
I hope you have better luck than me with the motor. I’ve had 3 fail on me. I was like you and thought since I had the motors in hand, even though the company had folded, I’d carry on trying to make them useful. I now wish I hadn’t bothered.
First was mechanical. Big crack/bang/thud when riding and then started acting very weird. I had a spare so didn’t even look to see what the issue was, just swapped it out. The second never worked at all. I could connect to it using the app but it just never actually activated when riding. Swappped that out for another which went the same way as the first after about 3km.
I’d like to think at some point I’ll pull them apart and try and repair them, but I suspect they’ll be sitting where I left them in about 10 years time.
Damn, that sucks. I know mine works as it’s been up and down the terrace a few times, so that’s something I suppose. We’ll have to see on longevity. At least with mechanical failures, it might be possible to source replacement parts, either off-the-shelf or custom fabbed - whether it’s worth the effort is a different question. And they claimed the motor itself was designed for easy disassembly and servicing. Electronic failures are a different story though. How many of their motors, batteries, etc. did you get?
