# Motor recommendations for 16% climbs?

#### Blufires

##### 1 µW
I've got this 2005 Kona Stinky downhill/freeride bike with BMX handlebars fitted (for a comfy upright posture, straight back when standing) that's an absolute riot to ride down the 5 acres of steep hillside that my house is on. I just don't want to pedal back up the 16% (9.2°) average slope every time I go to get the mail, check on the plants etc. So I'm planning an electric conversion for the specific purpose of riding around my yard. I might also tow empty wheelie bins or a trailer with <50kg of tools up the hill. The bike is about 20kg and I'm about 100kg. So by my calculations I'll need 170*9.81sin(10)=289.6N of force or 289.6*(26/2)*(25.4/1000)=95.6Nm of torque at the wheel plus a margin to allow for acceleration. So while a JetCat engine with 30kg of thrust would push me up the hill, I'd like something quieter. A bit more math gives roughly 12km/h for every 1,000W at that torque output. So if it's a hub motor it needs to be very low geared or absurdly powerful (6kW at 72km/h is the same torque).

* I've thought about a Bafang mid drive, but it seems like power is pretty limited and it kinda messes with ground clearance.
* Is there a 2-3kW cargo bike hub motor with a high enough turn count motor to only do 36km/h on the flat? The bike has a standard quick release dropout for the rear wheel.
* I've also thought about building my own mid drive using a 2,000W 190kV RC helicopter motor mounted to the seat tube in front of the rear wheel and a custom belt drive using HTD-5M belts. I've already done this with some success on a 16" children's bike, so this would reuse the parts. I'd need to gear it very low, so a two stage reduction belt drive would be necessary. This could drive the rear wheel either through a Nuvinci hub I scored for \$30 or a ~170mm belt pulley mounted behind the 200mm brake rotor (the caliper is at the back, out of the way).
*I also thought about the time the custom mid drive would take to build and thought maybe it's better to just earn money with that time and buy a huge hub motor instead, but it seems like they're all geared for flat ground speed, and what I need is 10-30km/h with huge torque.
*Maybe I should just buy a Surron, but I like the idea of this being lighter (due to lipo battery for short range needs) and using better quality suspension parts (fork is a Boxer).

Anybody got experience with stupidly powerful builds on very steep terrain? Bonus photo: the 2,000W 16" children's bike drivetrain.

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16% isn’t too bad, but I wouldn’t use a geared hub unless it’s a short climb, since you can’t shed the excess heat. A 1000w-1500w direct drive hub with Statorade for cooling should work. The 1500w will run cooler, but with a little pedaling I’ve climbed pretty steep and moderately long climbs with a 1000w hub running at around 2000w.

Edit: a temp sensor in the motor adds peace of mind

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Acres is a square footage measurement, which can actually be rectangular, so i'm not sure how this convert this into miles.
I'm envisioning that this is less than a 10th of a mile, which means any motor gets tortured in this case, but you won't build enough heat to blow something due to the short duration.

I think even my trusty leafbike 1.5kw would totally melt even with the advantage of being in a 22" wheel. It needs to shed >1000W in this condition: Motor Simulator - Tools

You might even melt a 50mm wide cromotor hub ( a ridiculously oversized motor you can no longer buy )

In this case we are producing 800W of heat... even if you add ferrofluid.. you may still melt it. It's just a lot of heat!

What a hub motor will do for you is provide adequate regen braking as you go down this hill. Most bike brakes aren't up to this task, it's an incredible rate of heat to shed. We'd really need a 16" wheel to make a hub motor work.

Mid drive? we lose regen which is really bad.

RC motor with the correct reductions would be the way to go, if you have the means.

* Is there a 2-3kW cargo bike hub motor with a high enough turn count motor to only do 36km/h on the flat? The bike has a standard quick release dropout for the rear wheel.
Any typical hubmotor at the torque levels you're after will need torque plates enhancing or more likely replacing the dropouts with something like one of the ones in the Torque Arm Picture Thread (or elsewhere), that clamps / pinches the axle flats.

The QS205 might do what you're after (QSMotors will probably wind it any way you want).

The GAA Grin All Axle motor from ebikes.ca has a new wider stator version, and has a torque arm design that can probably handle the torque required, rather than using tiny axle flats like almost all hubmotors do.

I don't know that it could give you the torque you want in the wheelsize you have, but the GMAC from ebikes.ca has a round axle that would fit in the dropouts and like the GAA a torque arm design that might handle the torque from a smaller wheel. I also don't know how long you could run it at your power levels without overheating it. The motor simulator at ebikes.ca can be used to check that.

* I've also thought about building my own mid drive using a 2,000W 190kV RC helicopter motor mounted to the seat tube in front of the rear wheel and a custom belt drive using HTD-5M belts. I've already done this with some success on a 16" children's bike, so this would reuse the parts. I'd need to gear it very low, so a two stage reduction belt drive would be necessary. This could drive the rear wheel either through a Nuvinci hub I scored for \$30 or a ~170mm belt pulley mounted behind the 200mm brake rotor (the caliper is at the back, out of the way).
For this you might look up Matt's drive, shown on a bike in this thread

The NV hubs are pretty heavy for what they offer, and they have an input torque limit beyond which they'll slip or be damaged. I'm not sure it's enough to do what you want; you'd have to check the spec sheets.

*I also thought about the time the custom mid drive would take to build and thought maybe it's better to just earn money with that time and buy a huge hub motor instead, but it seems like they're all geared for flat ground speed, and what I need is 10-30km/h with huge torque.
With a single-speed drive, for huge torque while at your highest speed, you'll need to set the system up for much more than your highest used speed, which will make it less efficient at the lower speeds, since motors' power peaks halfway thru the speed band where the torque and speed cross. (see the ebikes.ca motor simulator if you haven't run across it already).

A multi-speed drivetrain between motor and wheel would let you move the torque range up and down as needed, but it adds complexity and falure points. For the kind of power you're after, a lgearbox might work best, but if you use strong enough sprockets and chains you can look up Thud's 2-speed dog-clutch from a decade or more ago for something you can make that would be small and light. This page has a clear-cased plastic version to see it's internals; there should be an actual thread for it here somewhere too.

There's a thread with a number of 2-speeds here

Anybody got experience with stupidly powerful builds on very steep terrain?
Most of the ones I've seen over the years here used some form of middrive, sometimes DIY, sometimes kit. I don't have any specific links ATM but if I remember any I'll put them in here.

Bonus photo: the 2,000W 16" children's bike drivetrain.

You should look up LiveForPhysic's "Deathbike". (there's a youtube video of someone's attemped test ride..."and you know this bike is dangerous?...." :lol: )

One with a high-rpm BLDC motor and belt/chain transmission, sounds great
(sorry just noticed -no subtitles and videos are in Polish)

another one (built by professionals), for serious mountains

Acres is a square footage measurement, which can actually be rectangular, so i'm not sure how this convert this into miles.
I'm envisioning that this is less than a 10th of a mile, which means any motor gets tortured in this case, but you won't build enough heat to blow something due to the short duration.
Hard to tell what the distance is with only the 5 acres to go by, but I'm assuming not very long. The Grin 8T should be able to go up a 0.567 mile at 16% hill with a 330lb load at 20 mph @ around 2500W, with some pedaling.
or without pedaling:

In those simulations, the motor overheats in 1.6 minutes which may be longer than the travel duration.

Ferrofluid really does help, but i'd do this with a larger motor plus ferrofluid.

In those simulations, the motor overheats in 1.6 minutes which may be longer than the travel duration.

Ferrofluid really does help, but i'd do this with a larger motor plus ferrofluid.
Yes, 0.567miles is 1.6 minutes at 20 mph, but I'm guessing the distance is half that. Bigger is better, but if you only have the one hill, then it could be overkill.
We had a similar situation when I was growing up on a farm. House was at the top of the hill, mailbox at the bottom. My job was to walk down to get the mail, but when I turned 5, my dad got me an old go kart like this one. I had to learn how to do manual 3 point turns (pushing for reverse), since the gravel driveway was too narrow to turn around. It was a similar grade.

OK, you can technically do it, but what if there's wind..

RH212's diameter and additional poles really help here. It lasts 2.3 minutes without ferrofluid. About 14% more efficient.

Motor Simulator - Tools

We could do way better than this with a RC motor with a 2 stage reduction. Power consumption could be 1000w less, meaning we could get away with a smaller and cheaper battery. 69.5% efficiency is still bad.

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RH212's diameter and additional poles really help here. It lasts 2.3 minutes without ferrofluid. About 14% more efficient.
That's close to a mile before melting (0.935 mile), not bad considering the mass.

Yeah, far from the most efficient motor on the flat but the extra diameter and additional poles really make a difference on hills.

No ferrofluid required is nice.

24" is actually the sweet spot for this motor if your aim is to produce as much torque + speed as possible.
Scenario looks a little better in 22". Also, a 22" in a 26" bike is most ideal if you have vbrake posts because 24" tires want to collide with them.

I can't find the magic pie on the simulator but it might be an even better fit. I think it is like 16lbs though.. versus 12lbs for the RH212.

Thanks for all the help everyone.

The hill is 200m (0.12mi) long. The climate in Brisbane is the same as Miami, so cooling from the air isn't great.

In terms of braking: I don't need regen because that just heats the motor, controller and battery on downhill runs when they could be cooling down and any battery which can handle the current draw of the motor will have way more capacity than I need anyway. This is a bike that was used by energy drink sponsored professional riders on ski lift serviced mountains in its day, so I don't think the 200mm hydraulic brakes will struggle even with all the added weight.

A 24" wheel is quite limiting for tyre options isn't it? I wouldn't mind the 8% lower gearing though, and it would allow a wider (3-3.5") tyre to fit. Perhaps even a dirtbike tyre, where 24" is more common. I'll need a lot of traction if I'm towing uphill. There are no Vbrake posts.

I'm guessing ferrofluid works like transformer oil but it stays on the magnets without the need for seals and some of it jumps across to the stator when at full power? Seems like an OK idea as long as you never need to do any work on the rotor.

I've heard Nuvinci hubs are beasts that can handle far beyond their rated torque for ebike setups, although the original 180% range ones are a lot heavier and stronger than this newer N360 and people apparently run 5kW through those, so I was thinking 2-3kW would probably be ok with this one. It would be nice to be able to move part of the reduction drive into the hub for tidiness. It underdrives at a 0.5:1 ratio.

I Like the QS 3,000 option I guess with radio spokes you might be able to put it in a 24 in or probably find a moped rim that will clear your frame. Does it have rear disc brakes at the moment ? Yeah make sure things fit before you buy them. Maybe even make a cardboard box the size of your battery to see where the best fit.
Okay you have a rear disc brakes how wide is the dropout in the rear 135 mm or bigger ? As this may limit you with an aluminum rear. Here's something I know nothing about but it looks pretty sexy 40 mm magnets oh no 200 mm dropouts.

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### 2005 Kona Stinky GNG 1.0 build (mid-drive Stink-E) ABANDONED​

There are a ton of good options in 24" wheels.
22" is mostly BMX tires and 18" motorcycle tires that start at 2.5" wide.

22" might be too much of a drop in the rear, IDK. I had to use shorter cranks when running a 20" rear on a 26er.

You got the right idea about ferrofluid.
0.12 miles, you probably don't need ferrofluid.
Just a battery that can dole out about 55 amps!

Make a box for that triangle then after that see what would be a better fit 18650 or 27100 cells. As there are 40amp cell out there and 3 or 4p 14s ? 42 or 56 cells 21700.
Ok we got the battery. Oh Put the rest of the battery in the wagon.
One more thing 3p in a triangle for ez pyramid triangle Legos. Not how big is that triangle ?

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Besides the hill, what are the rest of the riding conditions going to be like? 200 meters is only a fraction of your riding, and there are many options to solve for that: so the question should be which of those options work best for the other 90% of your riding.

Why build this bike. It's nice.
Cut up some other bike and make it your mule wagon.

I've got this 2005 Kona Stinky downhill/freeride bike with BMX handlebars fitted (for a comfy upright posture, straight back when standing) that's an absolute riot to ride down the 5 acres of steep hillside that my house is on. I just don't want to pedal back up the 16% (9.2°) average slope every time I go to get the mail, check on the plants etc. So I'm planning an electric conversion for the specific purpose of riding around my yard. I might also tow empty wheelie bins or a trailer with <50kg of tools up the hill. The bike is about 20kg and I'm about 100kg. So by my calculations I'll need 170*9.81sin(10)=289.6N of force or 289.6*(26/2)*(25.4/1000)=95.6Nm of torque at the wheel plus a margin to allow for acceleration. So while a JetCat engine with 30kg of thrust would push me up the hill, I'd like something quieter. A bit more math gives roughly 12km/h for every 1,000W at that torque output. So if it's a hub motor it needs to be very low geared or absurdly powerful (6kW at 72km/h is the same torque).

View attachment 347113

* I've thought about a Bafang mid drive, but it seems like power is pretty limited and it kinda messes with ground clearance.
* Is there a 2-3kW cargo bike hub motor with a high enough turn count motor to only do 36km/h on the flat? The bike has a standard quick release dropout for the rear wheel.
* I've also thought about building my own mid drive using a 2,000W 190kV RC helicopter motor mounted to the seat tube in front of the rear wheel and a custom belt drive using HTD-5M belts. I've already done this with some success on a 16" children's bike, so this would reuse the parts. I'd need to gear it very low, so a two stage reduction belt drive would be necessary. This could drive the rear wheel either through a Nuvinci hub I scored for \$30 or a ~170mm belt pulley mounted behind the 200mm brake rotor (the caliper is at the back, out of the way).
*I also thought about the time the custom mid drive would take to build and thought maybe it's better to just earn money with that time and buy a huge hub motor instead, but it seems like they're all geared for flat ground speed, and what I need is 10-30km/h with huge torque.
*Maybe I should just buy a Surron, but I like the idea of this being lighter (due to lipo battery for short range needs) and using better quality suspension parts (fork is a Boxer).

Anybody got experience with stupidly powerful builds on very steep terrain? Bonus photo: the 2,000W 16" children's bike drivetrain.
View attachment 347114

I rode up such inclines in North Van hiking trails weekly if not daily at walking speeds on a Motorino XPH and a lithium LIFEPO4 emotorcycle. Steve Miloshev hub motors and controllers that were tricked. However..I would not do that on any other lithium unless my charger was 100% shielded from vibrTion.

That experience made me 20 years younger

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