How good is the Big Bear on hills?

[Deleted member 4366]

d8veh, I have a 500w rated 20 kph top speed DD hub running at 36v and 30 amps and it can't climb upto my house without assistance, although it is brushed.

What's its no-load speed. Throwing more amps at a DD motor won't convert it into a torque monster. Torque on a DD is dependent on the winding speed, but it will never compete with a geared motor the same size. A motor like a 500w BPM at the same current will get a 5:1 mechanical advantage (torque multiplication) because of the reduction gears.

 

[trex]

for comparison, the TCM crank drive motor has a reduction ratio about 24.

 

[Deleted member 4366]

for comparison, the TCM crank drive motor has a reduction ratio about 24.

Do you think that size might matter?

 

[trex]

yes, it does. The TCM's total weight is about the same as the BPM, 4.8kgs, but its inrunner motor alone weighs 2kgs, so the inrunner is about 40% in size compared to the BPM and yet, I reckon its climb ability is about 75% of the BPM. That goes to show how useful the crank drive technology is.

this is the TCM 2013 first generation:

The 2014 second generation is beefier but not much heavier, then you get to the BBS02 generation, even more capable then you get to the modern Max Drive generation. The crank drive technology will keep on delivering for some time yet.

 

[selrahc1992]

Evening all,

A friend of mine is considering a Big Bear after I made him aware of Woosh bikes. We are in rural mid Devon and it is quite varied, hilly terrain. I have BBS01 crank drive on my bike.

By all accounts the Big Bear is pretty powerful and copes with hills well. Just wondering what experiences are with mixed terrain. I considered a Big Bear myself so would be intrigued to see how one performs.

Cheers,
Paul

IMHO you'll find a fair amount of fundamentalism (crank vs hub drive) on this forum. ive got an oxygen 250 W hub drive, ive built a 2.5kw BPM 500W and ive tried a TCM crank drive belonging to a friend a lot. Your original post made me wonder what I'd do if i had to start all over again and teh truth is i'd probably go for teh cheapest rear hub kit i could find - even teh smallest bafang hub drive will easilly power upalmost any hill with a non disabled cyclist weighing less than 110kg. anything more powerful - to me - makes it something different from teh je ne sais quoi of being a bicycle and takes away teh exercise part, and persoanlly i think crank drives exceed teh design parameters of bicycle drive trains and cause maintenance issues, but youd know more about that having a crank drive.

 

[safetyfast]

persoanlly i think crank drives exceed teh design parameters of bicycle drive trains and cause maintenance issues, but youd know more about that having a crank drive.

Quite possibly, time will tell on that one, though I expect to have replace the chain and cassette somewhere along the way. I do think, however, the way that it is ridden has a huge bearing. I always cut power when gear changing and there is no crashing.

I remember in 1992 when I fitted a 1275cc engine to my Morris Minor but continued to use the original 1100 gearbox. Some people said the 'box wouldn't last two minutes. Twenty three years on it doesn't feel any different...

Thanks for all the comments on this, very interesting and useful.

 

[mfj197]

Quite possibly, time will tell on that one, though I expect to have replace the chain and cassette somewhere along the way. I do think, however, the way that it is ridden has a huge bearing. I always cut power when gear changing and there is no crashing.

Yes, I'll be interested to see how the chain and sprockets wear on my BBS01 conversion. I don't think it exceeds the design parameters of the drivetrain - an 80kg person can exert a torque of 137Nm at the crank just by standing up on the pedals which is way more than the Bosch Gen II 60Nm or the BBS01 80Nm. If he wears cleats, make it more like 172Nm (calculations here). But yes, changing gear whilst powering must reduce the lifespan.

Michael

 

[JohnCade]

Yes, I'll be interested to see how the chain and sprockets wear on my BBS01 conversion. I don't think it exceeds the design parameters of the drivetrain - an 80kg person can exert a torque of 137Nm at the crank just by standing up on the pedals which is way more than the Bosch Gen II 60Nm or the BBS01 80Nm. If he wears cleats, make it more like 172Nm (calculations here). But yes, changing gear whilst powering must reduce the lifespan.

Michael

But the motor isn’t working on its own, you are putting your power in too. So that can easily add up to way over 137Nms.

I can’t remember now how may miles my road bike chains lasted but I replaced them every season mostly, and the expensive parts either side lasted a lot longer that way. But my Kalkhoff chains are lasting around 1500 miles before I would start to damage the sprockets. I live in a hilly area which is hard on chains even unpowered. Woosh told me that the CD Sport I briefly had would need a new chain at around 1500 miles too.

 

[mfj197]

But the motor isn’t working on its own, you are putting your power in too. So that can easily add up to way over 137Nms.

I can’t remember now how may miles my road bike chains lasted but I replaced them every season mostly, and the expensive parts either side lasted a lot longer that way. But my Kalkhoff chains are lasting around 1500 miles before I would start to damage the sprockets. I live in a hilly area which is hard on chains even unpowered. Woosh told me that the CD Sport I briefly had would need a new chain at around 1500 miles too.

Yes, that certainly is true. But then how many ebikers are standing on the pedals whilst using full assistance? Do you change your chains more often than your sprockets? My old road bike has made it to 7,000 miles on its original chain and sprockets but I've already bought a spare of both for my ebike. My commute is pretty flat and I hope I get more than 1,500 miles out of a chain - that would be me changing perhaps once every 8 weeks!

Michael

 

[JohnCade]

Yes, that certainly is true. But then how many ebikers are standing on the pedals whilst using full assistance? Do you change your chains more often than your sprockets? My old road bike has made it to 7,000 miles on its original chain and sprockets but I've already bought a spare of both for my ebike. My commute is pretty flat and I hope I get more than 1,500 miles out of a chain - that would be me changing perhaps once every 8 weeks!

Michael

Yes I changed the chains before the rest. I had quite expensive Campag groupsets and chains were a lot cheaper to replace.

I can understand why some people advocate running it all longer and wearing it all out together on commuter bikes. But with expensive road parts it’s best to change chains in good time, and I suppose the habit has stuck. I’d rather change a chain regularly than the sprockets. I had different cassettes for the road bikes too which I used to change depending on terrain, and they would soon get ruined if paired with a worn chain.

 

[mfj197]

Interesting, thanks John. I've just bought the same chain and sprockets as are on the bike - £8 for the chain and £10 for the sprockets. For that price I'll probably just run them both until they start skipping - unless it is likely to damage the front chainring? I don't have a spare for that (and I should get hold of one).

Michael