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  1. #1
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    High torque low rpm motor for hills.

    I am looking for a 24v high torque dc motor that can move 600 pounds at least 10 mph on flat ground and climb a hill at 20% grade,on a 16 inch wheel for a pusher trailer.

    How many rpm should the motor be and what kind of size of gears should i use.

  2. #2
    Senior Member chas58's Avatar
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    All electric motors are high torque. What you need to do is match the optimum motor RPM with your wheel size and target speed.

    If you are more concerned about power than speed, you could get a low RPM motor designed for a 26” wheel (say 200rpm) and use it with your 16” wheel. That is going to limit your top speed to about 10mph, but you won’t burn your motor up trying to run it at a speed that is too low for it to be efficient.

    Torque really isn’t a problem, it’s just keeping your motor running at an RPM range it is happy at. If you are really worried about hills, you are going to want a high amp package more than high volts.

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    Thanks for that

  4. #4
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    Quote Originally Posted by batrike View Post
    I am looking for a 24v high torque dc motor that can move 600 pounds at least 10 mph on flat ground and climb a hill at 20% grade,on a 16 inch wheel for a pusher trailer.

    How many rpm should the motor be and what kind of size of gears should i use.
    This query is very similar to one I want to make, so I'll do a little piggy-backing on it and maybe start a new thread later.

    The differences between this and what I want to do are as follows. I don't care about the voltage of the motor and I hope I do not encounter any grades steeper than about 6%. Also, I don't plan to use the motor on flat ground, but only want it to help me (and the wife--it's a tandem) up hills. Also, the wheel will not be on a "pusher trailer"; I did some experimentation with a home-brewed pusher trailer and decided I didn't really like that approach.

    As to similarities, I do have a 16" wheel on the front of my bike, and the total weight of the rig, including riders and gear, is close to 600 pounds.

    In the way of observations, I hope your trailer has some kind of really heavy duty connection to the bike and beefed-up swivel joints. That's some seroius stress pushing that kind of weight up a grade that steep.
    Last edited by wayover13; 04-08-13 at 12:52 PM.

  5. #5
    Senior Member chas58's Avatar
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    The nice thing about tandems is that they are good at carrying weight. A pair of light riders and some panniers, and I’m easily at 500lbs gross weight.

    You just want it for some hills? There is something out there called hill topper, but any small motor will work.

    Electric motors have tons of torque starting at 0 rpm, so I don’t think that is a worry. You just need to make sure the motor is running efficiently at the speeds you want. If your motor is happy doing 25-30mph, and you are running it at 10mph, the motor will not be efficient, you will make lots of heat, and sooner or later something will give out.

    Your average rider in good shape can probably do 200 watts. So your smallest motor putting out 250 watts is putting out more power than your average rider. It is rather like the difference if your wife is pedaling strong on the tandem vs letting you do all of the work.

    If you are just looking to supplement your legs, any small motor for a 26”-29” wheel should work. They start to max out around 16-17mph, so they won’t be too fast. A 4 lb hub motor is going to keep your bike from getting too heavy too.

    If you want speed, you want volts.
    If you want torque, you want Amps.

    Anything bigger than a 250 watt motor will be a lot stronger than your legs.

  6. #6
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    Quote Originally Posted by chas58 View Post
    You just want it for some hills? There is something out there called hill topper, but any small motor will work.
    Thanks for that information: I'll have a look. Yes, smoothing out the terrain a bit is what I'm looking for. I expect to pedal when I get on a bike, though it would be nice if I could pedal a bit less strenuously on uphill inclines.
    It is rather like the difference if your wife is pedaling strong on the tandem vs letting you do all of the work.
    You seem to have some experience riding a tandem together with your wife
    If you are just looking to supplement your legs, any small motor for a 26”-29” wheel should work. They start to max out around 16-17mph, so they won’t be too fast. A 4 lb hub motor is going to keep your bike from getting too heavy too.
    Yes, extactly; we just want to supplement our legs. Our uphill speed can drop as low as 5 or 6 miles per hour, so the motor should operate optimally in the sub-10mph range. If we're going faster than 16 mph, it should be either because we have a strong tailwind or because we're going downhill: I don't want the motor to play any role in top speed. This cycle has 20" and 16" wheels, by the way.
    If you want speed, you want volts.
    If you want torque, you want Amps.
    Amps as far as the motor rating goes? Or amps in terms of the battery's rating?
    Last edited by wayover13; 04-08-13 at 02:17 PM.

  7. #7
    Senior Member chas58's Avatar
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    I posted this in part to help you, although it is set for 26" wheels.
    http://www.bikeforums.net/showthread...-(RPM-amp-mph)

    You can get an idea what the top speed is at different power levels for different small motors. Most motors have a "high torque" and "high speed" wind of the motor. You want the "high speed" wind because you have small wheels. Unfortunately "high torque" does not mean high torque, it means the engine will operate efficiently at low speed. Take a look at that info, and the table at the top to see if that helps.

    If you are pedaling, you probably are not going to run out of amps - that would be more important if you wanted the motor to take you up the hill by itself, carrying 600 lbs.

    The amp is mostly for the battery and the controller. With out BOTH of those, the motor will not get the power to it. And of course, the motor needs to be able to take the power. A small motor like the Cute 100 probably will not take much more than 12-13 amps for an extended duration (if you give it to the motor, something will overheat or break), while a 1000watt motor will need a battery and controller and motor that can take close to 30 amps.

  8. #8
    Doug CaliforniaEbike's Avatar
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    Hello batrike,

    I always love a challenge but why 24 volt? I think you'll find plenty of options if you can use 36v or 48v. we have developed an excel calculator for MAC hubs with 5:1 gear ratio and it would be possible to move your load as described at about 10.5 mph but with a 36 volt or 48 volt system.
    Best of luck to you
    Doug
    califronia-ebike.com

  9. #9
    Doug CaliforniaEbike's Avatar
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    Dear wayover13, I would agree with chas 58. If you only want assistance on the hills and nothing steeper than 6% a small hub motor would be quite adequate. In this case I would make sure it is a "geared hub" so that when you are not using it, it will free wheel and not add drag from the magnets. A 200 watt to 500 watt hub motor should do quite well.
    Doug
    califronia-ebike.com

  10. #10
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    Thanks for the helpful replies in this thread; I'm learning some things. In my area, on the paved roads I stick to, I suppose there may sometimes be short sections of grade that exceed 6%. But I'm going to guess it doesn't get much steeper than 8% even there. I should probably double-check that before I get too canonical about it though. But in any case I stick to paved, developed back roads, so whatever is considered extreme grades on such surfaces is the steepest grade I hope we'll confront.

    I've been looking at 1000 watt motors, being somewhat unsure what I'd need in that department. I do already have a 1000 watt, 48 volt direct drive hub-motor I got off eBay and have been experimenting with for a couple of years. That experience has convinced me that, yes, I do want a geared hub-motor when it comes time to upgrade. So that's what I've begun looking at. If I can get away with a 500 or lower wattage motor, I'd rather do that.

    Most recently, I discovered MAC hub-motors. I'd been looking at BMC since I'd read some good reviews on them. But I spoke with a dealer today from San Diego who said they'd moved away from BMC and are now selling MAC motors, the reason being that they feel the MAC motors are better supported by the manufacturer. So I'm now starting to look at these too. Can anyone offer testimonials on MAC motors, or remark on how, in their experience, MAC motors compare with BMC or any other brand of geared hub-motor?

    Thanks,
    James

  11. #11
    Senior Member chas58's Avatar
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    yeah, guess you got your answer in endless-sphere.

    I was thinking a 36v 500 watt with a 9 mosfet controler giving about 22 amps would do well. because of your wheel size and need for hill climbing ability, the 12t MAC motor would be good. at 200 rpm, its not going to give you a lot of speed on a 26" wheel. So, are you putting it on the 20" wheel? that is good for about 12mph, maybe too slow. doing teh 10T 250rpm motor on a 20" wheel will give a top speed of about 14.5mph, which may be better for what you need?

  12. #12
    Senior Member Trikin''s Avatar
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    i'm using a 500W Crystalyte front hub motor in the 16"wheel on my BOB trailer. The 36V Lit-Ion battery is mounted to the trailer deck and still provides me with plenty of cargo space for all my tour equipment. The torque is adaquate and when regulated through the throttle can push up most surfaces. I've been able to achieve over 120K on a single charge while using the motor sparingly, mainly on hills.
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    Last edited by Trikin'; 04-13-13 at 10:30 AM.

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