brushless geared hubmotor comparison

[stompie79]

All

First off let me say I have "lurked" around this board for the last few years thinking about an e-bike and appreciate the knowledge and experience available.

I have decided that with winter coming up I will forgo the getting an Xtracycle and electrifying it, for now, and focus on my more immediate needs for something a little simpler and front wheel drive as my first attempt at this sort of thing. Plus my funding is limited.
My daily commute has a large hill (for me) to climb both ways and I mainly want electrical assist to help with this so I can ride without having to keep stopping to remove clothing and get to work and back again without being exhausted. For the remainder of the ride I am happy to keep mainly to pedal power. I'm also hoping it will allow me to tow my bike trainer which hasn't been an option as I have enough trouble getting myself and bike up the hill at the front on my apartment building.
Anyway as the hills will start to get icy soon I was looking at adding a motor to the front (with a studded tire) to give me two wheel drive and hopefully more balance and control. Being a engineering type (nerd I believe is how my wife defines it) I had a look at the torque and power requirements and what I typically produce myself heading up the hills. I also noted the legal requirements I need to follow only allowing me a max speed of 32kph (20mph) and 500W of continuous power. Using ebike.ca's simulator and my own calculations I realised I needed a geared hub with 36V and 35-40A to have the power to get everything up the hills and still stay within the legal speed limit.
Following HillBillys off road hill climbing adventures on this board it looks like these numbers are pretty realistic, substituting asphalt, a trailer and shopping/small child for rough terrain.

My questions are
1) Under 500W limits my options so I believe it's mainly BMC V1 and eZee hubs that fit, especially as I'd like to use disk brakes. Are their any others I've missed?
2) Is putting out 70 Nm or 51 ft lbs of torque through the front fork expecting to much? My donor bike will need a fork replacement anyway (suspension) so any suggestions on what might be up to the challenge?
3) It appears to me that the BMC V1 and eZee hubs are pretty similar but I think I've noted more quality issues with the BMC being reported. Is that fair, would you agree the eZee is likely to be more reliable?
4) 35-40A coming from the batteries thought the controller gives a approximate 1300W estimated peak but with motor efficiency only giving 450-550W of output power, at lower hill climbing speeds, does that mean the rest will be going straight to heating up the motor? Is that going to be far to much for these motors, will is significantly reduce their lifespan? It would likely only be for 5 minutes at a time.
5) I am having trouble finding suppliers in Canada that will provide these motors outside of a conversion kit. Most of the conversion kit controllers won't handle more than 20A so can anyone recommend a supplier that would let me just have a motor separately or substitute a more powerful controller. I've noted a few US sites that might but thought I'd tap the experience here rather than having to contact each individually about if they ship to Canada.

Thanks for your help

 

[lynchy]

Hi Stompie,

I'm by no means an expert in E biking but have been researching as much as possible for the last few months and have several different motor, controller and battery options that I'm testing and using. I'm from an engineering background.

I've actually got a motor fitted to my bike that is pretty much what you are describing. It is a 500W at 36V, geared hub motor with free wheel. It's very quiet, not silent but quieter than the 250W hub motor that I've used. Never managed to get it more than barely warm either, but to be fair, there's no hills round these ways and I can't keep it pinned for too long. Weighs about 4kgs. I use a 36V, 25A, 500W controller with this. Got a few different battery options to choose from but all are lifepo4 and none are bigger than 10Ah rating.

I would say that this motor is probably a little conservatively rated at 500W, it likes current. The 25A controller initially was current limiting and I sent it back to the manufacturer and after modifications it's now functioning OK. After the mods, the controller is ok for 48V also. Will have to put a current clamp on it and find out out what it's pulling at 48V. It was very easily overloading my 20A rated DMM at 36V, will let you know what it does at 48V.

Here's a pic of the motor. This unit is front mounted and without disk. There are also options to have a disk front motor but that is only 350W at 36V as far as I know. Will be visiting factory again soon to find out more details. As is it, running off 2 24V, 9Ah LiFePO4 packs, it pulls just under 30mph. The free wheel speed is very high, 70kph, about 500rpm. Now in a 26" rim, a smaller rim would maybe be a bit better and will try that in the near future. If you want to run a beefy motor such as this, rear wheel might be a better option and I believe that a 500W motor with disk and 6/7 speed freewheel is possible with normal sized dropouts.





I know it looks like sh** but it's doing it's job very nicely and at a price that would make you smile. Those little packs that you see are only about 2.5kgs a piece. They can also be configured fo 36V but your range would be pretty lame with a big motor like this. Lots of other nice battery options available too and they don't need to wrapped in shrink wrap

Whereabouts in Canada are you?