Need more hill climbing power

RustyKipper

100 W
Joined
Apr 13, 2015
Messages
117
Location
South Yorkshire UK the land of flat caps and wippe
Morning folks,

I wonder if you chaps could offer any advice about where I might source a rear 500W hub motor that would accept a 9 speed cassette. I have emailed GreenBikeKit but they don’t offer such a beast.

A little background info, I have a Garry Fisher Tassajara mountain bike (fab bike), the idea was to build a commuter to travel between Rotherham and Sheffield, a trip of 14 miles and some Very hilly terrain. I fitted an el cheapo ebay pie dish kit together with a 9Ah water bottle mount battery with a small addition 0f a 20Amp ammeter. The system worked very well indeed, it would provide assistance up into the low twenties where the current could be seen to tail off, the only issues were the hub motor was VERY obvious, Very heavy and when in the low 30’s would add quite a bit of resistance to peddling. The best bit is the bike is 100% solar powered as it is charged from my off grid shed every evening.

So swapped this system out for a Bafang (probably copy of) SWXK front hub motor, it is so much more stealthy and lighter and looks really cool with a 203mm disc. It does alas top out at about 16mph with a 26 inch wheel and a large 2 inch road tire, interestingly without the drag of the pie dish I can easily top 30mph and on one of the more monster hills have done 38 albeit a bit bum clenching. The motor does however bog down badly going up the same hill slowing to around 9mph, I have done the shunt mod so the maximum current is 18Amps so the poor little motor is being hammered!

I’m not after silly speed but want to climb these hills at about 20-25mph as they are very long and very twisty so the quicker I climb the quicker I can get out of danger. I need to climb about 700 feet on the way home from work, if it wasn’t for the hills I wouldn’t really need the motor assistance except for the fact that the firm I work for insist I do some sort of constructive work when I arrive.

So I’m thinking keep the front hub motor and fit a 500W geared hub to the back, obviously I would need a bigger battery ( higher discharge C rate) and a second controller. Unfortunately I cannot find a 9 speed capable rear. GreenBikeKit do sell a 500W mid drive unit, however as I have to bike past the South Yorkshire Police traffic head quarters twice a day on a shared cycle path it has to either be fully legal or dead stealthy. ( Quite often the boys in blue are out jogging before work so get to see the bike at close quarters!).

Sorry about the long post but am sure you fellas will have found it of interest, any motor advice would be greatly appreciated.
 
BMSBattery sell the 500w Bafang CST. It's a cassette motor, so you can use whatever gears you want. At 36v, it does about 22mph in a 26" wheel. If you need more speed, a 48v battery an S12S controller would be a good match. I doubt that you'd need the complication of the additional front motor.
 
Wow thanks d8veh, that sounds perfect!
 
The new model 9 continent motors are also cassette. Just another option. Grin sells them.

http://www.ebikes.ca/shop/ebike-parts/motors/m3007rc.html

700 vertical feet is a big hill, but I assure you it's not going to overheat a 9 c motor climbing at 15 mph. Only if you are so heavy or the hill so steep that you climb below 10 mph will you overheat a motor.

To climb a steep hill at 20-25 mph, you need a big ass motor. 3000w. But you don't need to climb it that fast. You just need the power to go it at 15 mph or so. I think your main problem is mostly just too few watts to climb the hill faster.

FWIW, you can get 9 speed screw on freewheels. So a larger gear motor on the back, feed it 25 amps of 48v, and if you still want more power, keep the front motor. But I think a decent gearmotor in the back, and you will climb fast enough to not overheat.
 
I'm trying to get my head around what kind of hills would allow you to fly down at the speeds you mentioned, steep indeed!
Using the Ebike CA sim.;
http://www.ebikes.ca/tools/simulator.html
And plugging in an 8.5% hill, a CST on 48V would need a 50 Amp controller(1500 Watts) to climb it at 25 mph. Obviously, too much for that motor. A more reasonable controller, like the S12P would get you up at 20 mph without over-heating.
Both Dave and I have built 2WD's with all 3 speed winds of the Q100's and I know he likes them too, but I agree with him, that for most folks, a single BPM on 30 Amps willout perform two mins on 15 Amps ea. And be a simpler install to boot. If I wanted to start a new build, I would use a BPM CST fre sure..
But, I think you might be looking at a problem I have encountered.
When you installed the Bafang frt, you had to file out the fork drop-outs, right? Try putting the original wheel back on and see what you think.
With my Cute installs, enough metal was removed, that I didn't think it would be safe to run it with the axle only clamped, with no support around it.
I showed it to a machinist friend, and he thought he could make spacers, but it looked complicated. Small bits, but not easy to make.
In your case, I guess a new fork wouldn't be that expensive.
Or you could run two mini's. Two mini's ARE more stealthy than a single BPM.
But it would have to be two Q100's, because I don't think your Bafang is avail. in a high speed wind and the are no Bafang CST's.
I know Dave is not a big fan of running two high speed mini's, but I run two in 24" wheels with bigger controllers with no problems. But I don't do lot's of big hills.
But if you are light and fit, you could get BPM performance with two mini's.
Just to give you an idea what I'm talking about, click on my first link below. I just updated the review, so you can skip most of the thread and read the bottom of page two.
 
One reason I mentioned the 9 continent motor, is that motor can take 1500w. Or for a short time, even 2000w, 48v 40 amps. Your hill seems long, but it's not. So go for 2000w.

48v 50 amps is 2400w btw, and would likely be pretty tough on a 9 c motor. 2000w will get a 400 pound bike and rider up an 8% grade at 15 mph.

9c 48v, 40 amps. It wiill do er to get up the hill at a reasonable speed without frying it. But it won't climb the hill at 25 mph. 25 mph up that grade will take a motor with wide magnets and 3000w or more. It won't be a motor that takes a 9 speed. But it will be a motor that never needs to shift down! :twisted: :mrgreen:

No need to shift down on a motor that can climb a steep hill at 25 mph. You won't be pedaling it, EVER. So a single gear is all you need, for an emergency pedal if it breaks down.

So that's the other option, a 3000w motor, and no need at all for 9 speeds.
 
For an ebike to do 25mph on a steep hill it needs to be able to do 40mph or more on the flats unless you have the speed artificially limited. Sorry but no little geared hubbies are up to that task.
 
Lots of Amps and a big DD hub, and you can build a fast climber.
A slow climber is better built as a mid drive.

Hubs can only climb steep and slow for short periods. They need spin and wind to cool down.
 
MadRhino said:
A slow climber is better built as a mid drive.

Hubs can only climb steep and slow for short periods. They need spin and wind to cool down.

I don't quite agree. It depends on the winding speed and type of hub-motor. The only problem is that you can't have good climbing and high top speed with a normal hub-motor, except if you have really high power. The Xiongda motor is tiny, but it can climb steep hills as long as you want because it has a very high reduction ratio in its low gear and high efficiency at low bike speed. The single-speed geared motors like a 12T MAC or code 15 Bafang BPM can also climb steep hills without overheating.
 
I'm certain sure I could melt a Mac 12 with ease. Simply load the bike too heavy, and go climb Augustine pass. Below 300 pounds total weight, no problem, but 400 pounds, big problem. Same goes for low rpm 9 continent motors. Bog down to 8 mph, you'll melt one.

The xionga motor is impressive. But it's going to take more power than it can take to go 25 mph up his hill.

But I don't agree that he needs to climb the hill at 25 mph. 12-15 mph will be plenty fast, to not melt any hubmotor down on that hill. 700' of vertical is a big hill, but it's not going to melt his motor if he can just go 15 mph. It will be over too soon to get much above 250f. So the xionga motor will get him up the hill just unless he's overloaded. Does it take cassette? That seems to be what he really wants.

For sure, you can melt nearly any hubmotor easy, if you grind up a hill too slow, for long enough. I melted one down real good once because the trail was so rough and rocky that I simply could not hold on faster than 5-10 mph. I could have climbed the slope easy, but I was getting bucked off too much to ride up it at 15 mph.
 
BURP. "...climb these hills at about 20-25mph as they are very long and very twisty so the quicker I climb the quicker I can get out of danger."

Hi. Just curious? "twisty" sounds like many chicane-type racing course turns (at slower speeds)? Any chance turn banks etc are unobstructed visually such that you can see "what's coming"/other traffic etc on the roads and at it's edges? Whether higher speeds in any way increase risks to you and other road users? Thinking that (slightly) slower speeds traded for (slightly) less fast/more times taken to do this trip might reduce risks in any way? Any posted speed limits? And typical speeds and max. speeds of *other* road users?
 
LockH said:
BURP. "...climb these hills at about 20-25mph as they are very long and very twisty so the quicker I climb the quicker I can get out of danger."

Hi. Just curious? "twisty" sounds like many chicane-type racing course turns (at slower speeds)? Any chance turn banks etc are unobstructed visually such that you can see "what's coming"/other traffic etc on the roads and at it's edges? Whether higher speeds in any way increase risks to you and other road users? Thinking that (slightly) slower speeds traded for (slightly) less fast/more times taken to do this trip might reduce risks in any way? Any posted speed limits? And typical speeds and max. speeds of *other* road users?

Two sides to the coin. :D

Head: Faster is safer sometimes, and ability to accelerate to high speed is always safer. For that is giving you more escape options.

Bitch: Slower is safer because you are unlikely to hurt yourself badly in a crash, as long as nut crashing with or by, another vehicle. :wink:
 
If using a 9c a 30 amp. controller and hills is all it can take till you start turning the winding a different color in time. 40amps yes but with lot's of hills, be careful. 48volts a must or higher voltage. 2,000 watts and put a hand on it to check for heat.
 
Oh Goody. "Faster is safer sometimes." Care to elaborate? And "ability to accelerate to high speed is always safer." OK! I've been advocating one million mile per hour vehicles as *MUCH* safer. Yes? Or is there such a thing as "too fast" perhaps?

Yah, at least we might agree that large, heavy "too fast" vehicles (w/occupants seated and strapped in) can be a threat to others? (Weapons of Mass Destruction)

"Fast" might be a "double-edged sword"? (Have known a few that were "fast" on their own two feet.)
 
Hey guys, sorry for the late reply.

The hill in question is about 2 miles long with varying degrees of steepness, the majority of the climb is around 15mph, but a couple of sections are down to 9 mph with me pedalling hard but not standing up, I am 168lb / 76Kg and reasonably fit. The road is a 2 lane country road but both sides have hedgerows so there are many blind corners, this is kind of the problem as cars tend to queue up behind me and there is often some right dodgy overtaking although 95% of drivers do seem to be surprisingly patient. I’m not really happy with this route and have recently started a new one, it is however 2 or 3 miles longer, much less twisty and less of a climb however this does add quite a bit of time to my commute which is the best part of an hour. My journey to work is mainly downhill and I like to keep to about 25mph although I am often spending quite a bit of time above 30 which I guess is getting a tad dangerous on a mountain bike even with road tires.

I’m thinking keep the little bafang on the front (now it has a disc brake) which works perfectly well around town as a pedelec when near people ect, but add a 500W bafang CST at the rear with a thumb throttle for use ONLY out of town which is not really natural territory for a 250W pedelec. Probably best if the motors don’t go above 25mph on the flat, that way when I come off doing 30+ I know it will be down to my own peddling! I’m sure both combined will give quite decent hill climbing.

I took a thumb throttle apart yesterday to see if I could make it a tad more discreet, interested to see it used a hall sensor and 2 magnets I was expecting to see a pot.
 
RustyKipper said:
Hey guys,...
I took a thumb throttle apart yesterday to see if I could make it a tad more discreet, interested to see it used a hall sensor and 2 magnets I was expecting to see a pot.
I doubt there's anything more discreet, advertized as a "universal throttle"(because it lacks voltage indicators haha) than this one:universal throttle again.jpguniversal throttle.jpg
Potentiometer throttles are available... at a (high) price and like all pots, are subject to wear (itchy AND scratchy)
 
RustyKipper said:
Hey guys, sorry for the late reply.

The hill in question is about 2 miles long with varying degrees of steepness, the majority of the climb is around 15mph, but a couple of sections are down to 9 mph with me pedalling hard but not standing up, I am 168lb / 76Kg and reasonably fit. The road is a 2 lane country road but both sides have hedgerows so there are many blind corners, this is kind of the problem as cars tend to queue up behind me and there is often some right dodgy overtaking although 95% of drivers do seem to be surprisingly patient. I’m not really happy with this route and have recently started a new one, it is however 2 or 3 miles longer, much less twisty and less of a climb however this does add quite a bit of time to my commute which is the best part of an hour. My journey to work is mainly downhill and I like to keep to about 25mph although I am often spending quite a bit of time above 30 which I guess is getting a tad dangerous on a mountain bike even with road tires.

I’m thinking keep the little bafang on the front (now it has a disc brake) which works perfectly well around town as a pedelec when near people ect, but add a 500W bafang CST at the rear with a thumb throttle for use ONLY out of town which is not really natural territory for a 250W pedelec. Probably best if the motors don’t go above 25mph on the flat, that way when I come off doing 30+ I know it will be down to my own peddling! I’m sure both combined will give quite decent hill climbing.

I took a thumb throttle apart yesterday to see if I could make it a tad more discreet, interested to see it used a hall sensor and 2 magnets I was expecting to see a pot.
I use a half twist and a thumb side by side and it works quite well, very intuitive;
http://endless-sphere.com/forums/viewtopic.php?f=4&t=40567
Scroll down towards the bottom of the page for pic.s.
You will need a stiff battery to run both motor simultaneously.
 
i like what you have created here....this is very interesting...i was curious if there was some sort of mid drive calculator on here. or somewhere....so if you are anyone else wanted to climb the hills with a mid drive how much power would you need....

iam stumped here on calculating exactly or around about weight ,gear ratio, and rpm and grade of hill and watts put it and ofcourse watts putt out.....distance etc..
 
That thumb throttle looks perfect, I had the standard type that looked awful, it was like a big wart, I found after fitting the pedal sensor the throttle became redundant so I removed it, my only gripe now is that when tooling along at 25 the motor is running all the time sapping power unless I hold one of the brakes in. I'm thinking of adding a little circuit to cut the power when the motor runs out of steam. I so wish I started this project years ago its turned a hellish commute to a totally enjoyable one, even in the pouring rain!

A mid drive unit would make a lot of sense as the shortest route home involves a climb of 20%, its just as difficult to walk up it, I have ridden it a couple of times but I've been overtaken by empty crisp packets blowing past!
 
You just need a motor that gives high torque. You don't need to limit your choice to a mid-drive.
 
I'm gonna go with gearing to keep motor RPMs up (re efficiency curves) at slower wheel RPMs (vehicle speeds). Assuming same diameter motor stator size/number of magnets/number of magnetic pulses per revolution. Also assuming same average vehicle target speed up hills as level/down hills. (Gravity your friend/enemy. As is "efficiency" aka "heat losses".)
 
Maybe in an ideal world I would go with maybe a 1Kw mid drive on a full suspension bike (roads here are shocking) but in the UK we have a 250W limit so anything more powerful has to be pretty stealthy, also at 35mph my feet are spinning like crazy, I guess with a mid drive I would need to tie my feet to the pedals as I believe there is no freewheel or I imagine the fire brigade would need to untangle my remains from the bike :oops:

OK I've just bitten the bullet and ordered a motor, controller and spokes from BMS Battery so will see what turns up. Such a shame GreenBikeKit don't do that exact motor as I have ordered from them before with good success.

Next big expense will be the battery, I'm planning on using some 12Ah headway cells with a bms, they seem to have a peak discharge of 10C, if I mount the battery pack on the rear carrier instead of using a water bottle mount it might stop me flying over the handlebars when I brake hard! as well as being super discreet. I do need to make the battery removable as I have to take it into work to charge it in the morning, quite handily we have a 1.5Kw solar tracking array in the car park and at home I have a 180W panel charging a big battery ready to charge the bike at night, there is no fun in using that national grid stuff that comes out of the wall! Also it is just so damn cool to plug the mains lawn mower into the shed, sometimes I even go outside and plug the hair drier into it to dry my hair just for the hell of it. 8)
 
How about a MAC 10-12 T Geared hub from http://em3ev.com/store/index.php?route=product/product&path=36&product_id=107

These are great hubs, 60-72 volts should give you the speed you need even on 10-12T ?

The 8T is great fun but the 10-12 T would be far better for regular steep hills.

10-12T and/or 20" Rim ? you'd probably need more than 72 volts in an 8T though with a 20" wheel. If you like to pedal the 20" wheel is out though.
 
so have you experiemented with changing up your drive train a little? maybe lowering crankshaft sprocket...and or raising gear cassette?
i noticed they make add one for 10 speeds..where you can just add a sprocket with like 44 t on back...i want to say like 100 bucks or maybe 80 kinda pricey but that maybe help...i am struggling with this stuff myself.....just tossing out ideas..thank you for providing a forum for discussion.
or if you had a middrive could you keep your gear set or change it up and add a little three speed hub...assuming your not using a rear hub motor.
 
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