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Old 06-30-14, 02:52 AM   #1
Wisco
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Recommended hub motor for fat bike with trailer/heavy loads

So, I'm building a Surley Pugsley (with a non-offset Moonlander fork) to be my winter bike, and I happened across a blog post showing a fat bike with a front hub motor. I'm intrigued, especially since I'm also planning on building a heavy-duty trailer to haul appliances and stacks of bikes/scrap wood/compost. An assist would be helpful when I'm hauling 500 lbs of steel across a frozen lake. (yes, I will be buying those studded 45North fatbike tires).

Specifications I'm looking for:
1. I'm not concerned with speed so much as torque, pulling ability, and length of battery life under extreme conditions both in terms of weather (last winter the temperature here stayed below -5 for two weeks straight) and heavy loads. I do have an external outlet at my house so the battery charge length requirement is variable.
2. I don't need or want a powered front wheel all the time, for example in summer when using the Pugs to go mudding for fun. So I'll be building two front wheels, one powered and one not. Therefore, I would prefer something with a battery and control system that is reasonably simple to switch in and out, not something with 20 different clamps, although I suppose if it's essential this requirement is subordinate to #1 .
3. This may be a moot point since I know almost nothing about e-bike control systems, but I would prefer something other than a twist-grip, motorcycle-style throttle since those can get dicey when riding with thick gloves.
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Old 06-30-14, 07:23 AM   #2
Kopsis
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You have a lot of studying to do.

Hub motors are available in different "windings" (how the copper coils are wound inside the motor) that allow you to chose your max no-load RPM. Generally, the lower the max no-load RPM (at a given voltage) the more torque the motor will produce. Also note that a planetary geared hub motor will generally produce more torque than a direct-drive hub motor.

The essential components of an e-bike system are motor, motor drive electronics, battery, and controls. For your application, I'd suggest mounting the battery and the motor controller in a small Pelican case on a custom front rack. That will help keep weight over the driven wheel. And, if done right, would make it pretty easy to remove the whole system with a minimum of fuss. I've seen this done on DH mountain bikes and it's a pretty clean solution. The alternative is putting the battery and controller in a bag/case on a rear rack. Not a bad approach, but you'll end up with less traction in front and you have to run the wiring harness the full length of the bike.

Off-the-shelf throttles come in three flavors -- full grip twist, half grip twist, and thumb. Depending on your fabrication skills, other variations are possible. High-torque motors tend to be difficult to modulate with the throttle, so you might find a simple on/off push-button is just as good.
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Old 07-07-14, 10:13 PM   #3
Tailor
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Quote:
Originally Posted by Wisco View Post
Specifications I'm looking for:
1. I'm not concerned with speed so much as torque, pulling ability,
Everything I've learned about ebikes since starting to look into them, indicates that a mid drive is capable of giving you much more of both. Mainly because it can use the gears of the drive train, and also becuase the motor doesnít have to fit into a hub, and can be a little bigger if thatís what you're needing.

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Originally Posted by Wisco View Post
and length of battery life under extreme conditions both in terms of weather (last winter the temperature here stayed below -5 for two weeks straight) and heavy loads. I do have an external outlet at my house so the battery charge length requirement is variable.
Although the literature indicates that lithium based batteries only take a small hit in the cold (heat is their real nemesis), my experience has been that charging them in the cold seems to take longer, and result in a slightly substandard charge. Another fun thing about lithium batteries in the cold (and this part you cant really do that much about unless you went with the back pack battery available on one of the ebike kits) is that while they are only slightly impacted by the cold, the lowered output makes them hit their low cutoff sooner, so it really feels like the batteries die a lot faster in those conditions.

Quote:
Originally Posted by Wisco View Post
2. I don't need or want a powered front wheel all the time, for example in summer when using the Pugs to go mudding for fun. So I'll be building two front wheels, one powered and one not. Therefore, I would prefer something with a battery and control system that is reasonably simple to switch in and out, not something with 20 different clamps, although I suppose if it's essential this requirement is subordinate to #1 .
If you go with a mid drive, you can simply remove the battery (doubly easy if you go with the "water bottle" style battery, which also lets you charge it indoors), depending on the type of mid drive, there are often ways to disconnect the motor from the drive train and then (depending on how deep your mud is) you might not even have to remove it.

That said, if the easy removal thing is a deal breaker, you might be stuck with a hub motor. Of all the things I've been seeking in my "perfect mid drive" kit, easy removal hasnt been on my radar, so its something I cant speak to.

Quote:
Originally Posted by Wisco View Post

3. This may be a moot point since I know almost nothing about e-bike control systems, but I would prefer something other than a twist-grip, motorcycle-style throttle since those can get dicey when riding with thick gloves.
Is pedal assist an option for you? A number of the kits have that. Depending on the controller and motor type, it can go from an additional .5x, to 4x+, making each pedal stroke anything from you plus a little, to superman on a bike. Not sure about front wheel drive pedal assist though, never seen that one.


In any case, best of luck in finding the system that works for you, and that you like.
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Old 07-08-14, 10:22 PM   #4
sculptingman
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Stay away from hub motors of any kind.
they are inherently weak, and suffer dramatic overheating and battery drain when under high loads at speeds outside their sweet spot.

a Bottom Bracket drive of maximum legal power, however, can run thru your gearing, and thereby enable you to keep the motor going at its most efficient speed while swapping torque for velocity or vice versa.

this will enable you to gear the bike for the loading you need it to handle, and offer the longest battery life with the least potential for damaging your drive thru heat.
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