Tuesday 5 July 2016

Ghetto ebike: Batteries & Mounts

Hi, I finally got round to designing and printing off all the mount parts I needed to allow me to mount the big batteries. Here are some pictures

It was actually more time consuming than I realised to design and print. Each mount took approximately ten hours each to print so I just set it to run and run while I went out to get bolts and screws. I'm really happy with the way it came out, the measurements were pretty much spot on for the tubing, and the bolt holes worked - I used hexagon holes at the back to help tighten the nuts without having to use a tool to tighten there. The batteries will be held over the top with straps, and there are some foam pieces for support of the batteries. They are held really tightly. I ended up using PLA as a print material and I am happy with how strong it is.

Fitting the Bafang motor set was fairly straight forward, I had no difficulty, I had all the tools needed. There is a nice guide to fitting the motor here:

I do recommend getting a 'Hollowtech II' spanner to help you to tighten the lockring for the motor. The only issue I had was that I cracked the plastic bottom bracket cup when removing the old unit but it was easy to saw through and remove once I had the thing removed by unscrewing the other side. I recommend looking up a video on youtube to help figure that process out.

I think, all that is remaining for me to do is solder a Y-harness to connect the batteries to the motor (in series 2 x 24volt batteries = 48v) which I will do after a cup of tea.

One issue I face from the setup is the notorious 'chain falling off' problem. I took the bike for a test pedal to check the brakes and gears, and of course the chain falls off the motor ring when trying to use the top two gears at the back. I didn't know about this before searching on the internet. There are discussions here here and here.

It seems that the BBS02 Motor has been designed with Hub gear units in mind, and not in general traditional multi-cog cassettes. Hub gears mean that the chain will not move up of down when shifting gear, it will always be in one position. By attempting to use standard cassette gear systems, the BBS02 has a flaw where the chain will fall off, usually on the upper two gears due to chain alignment issues. There seem to be people who have already experimented with solutions, and these range from a complete front chainring replacement (around £100), using a hub gear as mentioned (Anywhere from £300 to £1500), and also using a chain catcher device (£3 - £30). I will probably begin with fashioning a chain catcher first and seeing how that goes. It's a bit of a shame that Bafang does not function smoothly out of the box, the company should explain this in their advertising or better yet fix their standard rings with a few more millimeters offset. Grrrr.

When I ordered my motor kit, I chose a 46T chainring to be shipped with it, and right now, after my first test, I think it is too hard for both my gear range and local geography. I live in a somewhat hilly area (which is used for UK Tour De France races) so it can be considered not at all flat like the city. I think I would recommend a 36T chainring for my hilly roads, possibly even fewer teeth, but I will test and learn. The 46T is in my eyes even too hard for a cold start on flat (using my rear gear ratio). Ah things we learn!

- Was not true in real testing. It actually works quite well on the road and is nice and powerful with good pull.

So Things left to do are Wire harness making, and cheap chainring solutions. I wonder if PETG will be strong enough for a 104mm BCD adapter? Crazy suicide idea? Or cheap genius? 

No comments: