Posted by: Oliver in: DIY and tinkering
[See all project knee posts]
So I’ve decided to fit my existing bicycle with an electric motor. The problem is that most kits come with all the parts you need, including an insanely expensive Lithium Ion battery. Although small and lightweight for the power they produce, they do wear out in a couple of years and are rather prickly about how they’re charged – and of course are several hundred pounds to buy.
Since I’m already towing a trailer (15kg ish) with two kids (combined weight approx 30kg), I’m not really going to notice the difference between a 3kg £500 Li-ion battery and a 12kg £50 lead acid one. Unfortunately, you just don’t get kits with lead acid batteries, and it’s remarkably hard to find just a controller and motor without the batteries included. There are many suspiciously cheap battery-less kits on eBay (shipping from China) but I just don’t trust them.
Enter the excellent Electric Transport Shop, who a) will do me a custom job including some decent lead acid batteries, and b) know their motors so can sell me one which will actually work on Bristol hills (the Bristol branch sells a different motor to the one in Cambridge, for instance). They certainly aren’t cheap motors, but I’d rather spend a bit on one that will do the job.
Unfortunately it seems my bike’s carbon forks will have to be replaced. The motor is large and usually forks need to be bent a bit in order to fit it in, and of course you can’t bend carbon forks: steel is best.
Initially I really wanted to get forks with disc brakes, since going back down Park St in the wet with the trailer can be a bit nerve-wracking with V-brakes. However, the size of the motor means it’s hard to find disc callipers that won’t catch on the spokes. This meant I wanted to get forks which had both V and disc attachments so I could revert to V brakes if necessary. Alas, steel 700C forks with V and disc attachments simply don’t exist (there were some promising models but they turned out to be discontinued). So after much searching and help from Bike UK I simply got some very cheap (under £30) steel Raleigh forks with V brakes – discs will have to wait for another time.
(Bike are a brilliant shop who have been incredibly helpful since I arrived in Bristol in 1996 – I remember being a student and them happily lending me tools to fix my horribly old cheap bike on the pavement outside.)
So, the only remaining problem is: how do I attach 12kg of lead acid battery to my bike? Answer coming up in ProjectKnees #3 soon.