Front gearless hub drive for tandem

[brickelltandem]

Many sources sell a 750-1000w (dependent on controller) gearless front hub drive.
However, none appear to carry ratings RPM or rim-pull (unlike heavy construction equipment....)
We understand the controller is one deterministic factor, will be used with 48v LiPOH battery set.

We have been advised to procure a "lower RPM higher power" hub, e.g. 500w not 1000w but there is no RPM or copper coil count data to support this claim.
Is there a serious difference in pulling power and how can we tell for a given make and model?



This will be for a tandem, 26" wheels, 390 pounds weight or so. (Yes, Bafang mid drive is desirable but not an option for reasons of geometry and sanity.)
Thank you.

 

[amberwolf]

http://ebikes.ca/simulator
data shown in curves and readouts as you experiment is all from tested motors/etc.

 

[dogman dan]

Lets get one thing crystal clear right now. If all else is the same, a high rpm motor does not have different torque than a low rpm one. There is no "high torque version" despite most vendors selling them as such.

However, if the use is going to be loaded heavy, and the rpm extremely slow going up hills, the lower rpm motor will work more efficiently at low rpm. It will heat up less, and be less likely to burn out the motor on an extremely long steep hill. This can be an advantage as well, in stop and go city riding. Better efficiency is a good thing, if you have no intention of riding faster than 20 mph.


One US based seller carries the low rpm 6x9 (9 turn winding) winding direct drive motor. Here's the specs for it. If you can find the same type 28mm wide magnet motor in 6x9 elsewhere, such as in china, the specs will be the same. A different motor, such as one with wider magnets, will be able to pull harder than a 28 mm motor. Once you get into monster motors, the power is high enough to ride fast up hills. Then there is no need for lower rpm motors.

Brand: Electric Bike Technologies
Type: Direct-Drive (brushless, disc brake compatible)
Power: 500w nominal / >750w @36v / >1000 @48v
Max Torque: 39N-m @36v / 46N-m @48v
Max RPM: 194 @36v / 259 @48v
Cable: 8" axle exit, 3-phase / 5 hall effect
Connector: Round 8-pin 19/32" (10.4mm)
Weight: 12.8lbs (5.8kg)
Warranty: 2 Years (up to 48v)



It breaks the rules for me to sell stuff for my employer in this section of the forum. But you specifically asked for it. I work the on line chat there.

Most generic dd motors are 9x7 winding, or the faster 48v kits may be 10x6.

In 26" wheel and 48v the 6x9 will go about 19 mph, the 9x7 about 27 mph, and the 10x6 about 30 mph. With a tandem, a bit slower than those numbers because of the extra weight.

 

[wesnewell]

Read this then edit your first post.
https://endless-sphere.com/forums/viewtopic.php?f=3&t=66302
I don't think you will be happy with a 500W motor kit, and the cost difference between it and a 1000W kit is minimal. The 1000W kit may even be less.

 

[chas58]

So much to talk about here, where to start?

Like said above, high and low RPM motors have similar torque. I have both. Very little difference.

What is really critical in design is that you have the motor designed for your speed range. If you drive the motor with full power too slow, you will overheat and burn something out.

Are you climbing hills? If you are on a tandem, your motor has to be designed for climbing hills and will not help you on the flats.

I ride my tandem (no motor) at over 20mph flat. I really can't imagine a motor that could help me go up any significant hill and help on the flats, unless of course I used a mid drive. If you are only going 5-12mph, maybe a motor can help. But a tandem is a beast, needs a good bit of power. Taking one up hill on a hub motor is a recipe for disaster.

we would really need to know about you (and your stoker) the terrain you ride in and what bike you are putting this on. There is a guy in Hawaii who did this a while back - try searching on Tandem and Hawaii.

 

[d8veh]

It's true that high and low rpm motors give the same torque, but the question is whether you can use it. Both produce the same torque at low RPM, but the high RPM motor will have a lower efficiency, which will cause it to overheat, so it can't be used at low RPM.

The important thing is to ensure that you choose a motor that remains efficient in the RPM range where you'll be using it. The maximum RPM is a very significant characteristic in that respect.

Back to OP's question: I wouldn't fit a motor that draws anything more than 800w in a front wheel. It brings several problems. Firstly, you have to resist the torque. Most drop-outs aren't strong enough, even wit torque arms. It would be OK with strong steel forks. Secondly, the torque makes the wheel spin, especially on steep hills. I don't know how that would be on a tandem. Thirdly, the weight in the wheel (big DD motors) upsets the handling and steering a bit. If it were my bike, I'd be looking at a rear motor or mid-drive, if possible.

 

[Eteck]

gearless front hub drive

Are you set on front drive ?
For such a large heavy bike with two people that would require some careful thought on the front forks.

However, none appear to carry ratings RPM or rim-pull

It's hit or miss. Some have good specs listed. Such as this one:
600 max RPM and 35 N/M torque
http://www.ebay.com/itm/Quiet-48V-1500W-Front-Wheel-Brushless-Gearless-Hub-Motor-for-Electric-Bicycle-/331722706517?hash=item4d3c36ce55:g:5PYAAOSwAKxWVWG1

We have been advised to procure a "lower RPM higher power" hub, e.g. 500w not 1000w but there is no RPM or copper coil count data to support this claim.

I agree. I'd experiment with a decent lower cost 1500W motor and see how it performs.

Here's one I stumbled across that claims it has 58 N/M of torque, a little more than the typical hub. It's for rear wheel though.
http://www.alibaba.com/product-detail/DIY-1500w-high-power-brushless-gearless_60434918544.html?spm=a2700.7724838.0.0.B5RiGO

I

Is there a serious difference in pulling power and how can we tell for a given make and model?

I think you mean the N/M figure or torque rating, Most of the lower cost popular Ebike hubs are going to be designed around a normal 1 rider bike
scheme with a bias for greater speed as the voltage/power goes up. So there may not be a huge difference in the "basic pulling power"
BUT a hub with a higher power rating will be able to handle sustained loads better, such as your tandem bike, all else being equal.

 

[BigBird]

One hub motor that works well in steep hills with a tandem is the Bionx d500. It is NOT a front hub motor and is not cheap but is a good system. I have one on a Santana RIO 26" wheel road tandem and one on a Ventana ECDM full suspension MTB Tandem. Our typical rides are close to 100' of climb per mile and MTB rides are MUCH more than that. We are a 146 year old team and that doesn't count our 13 year old pup that nearly always rides with us.

 

[dogman dan]

https://endless-sphere.com/forums/viewtopic.php?t=79816

Not sure why he started another thread.

FWIW, pretty much beat to death he can't easily use a mid drive, or rear motor.