Front and rear motors - how to control?

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pengyou

If you had front and rear hub motors how would you control them? Would a standard controller do the trick? How would you turn one off when you didn't want it? Must they be the same wattage?

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johns

put it on a stand

Abneycat

You mean two at once, Pengyou? Well, you can use a dual speed motor controller. That will let you use two at once. The consensus on these though is that they just eat twice the power, and double your weight, while offering little extra speed. Primarily the gain is in torque, something you can obtain from a higher winding count hub motor or a good geared frame motor.

The efficiency on this sort of thing is pretty low.

pengyou

Thanks! I will scratch that option off the list. :) It seems to me that in order to benefit from two motors a bike is going to have to have gears attached to the motors to benefit from the extra power and torque. Two hub motors are still going to turn at the same rpm.

BroadwayJoe

The only reason I can see to do this is maybe some desired handling aspect on slick surfaces? Nevermind the cpu power that would be required to make something like this work in concert with traction control?

Utilizing gearing will always be the ideal way to provide widest range of torque/speed. Trouble is, it get's way more complicated and harder to execute cleanly. Since genuine eBikes can be pedaled, hub motors do make sense in that leg power can often help during those moments when motor/controller are just not at their best operating range. Considering the simplicity of BLDC hub motor design and it's ability to be used on just about any bicycle wheeled contraption, they're a great option.

Dual windings might be of use to you but IMO the best money is spent on as much voltage range and lithium chemistry as you can afford?

Abneycat

Some people find that dual winding count motors don't do exactly what it says on the tin, so to speak. I've got no personal experience with them personally though, asking over at visforvoltage would be a good thing.

My personal mantra in this case, is going with your standard hub motor, picking the right one for your needs, and then simply picking *the right voltage* for your needs. Broadway joe raises a good point. Keep your setup simple and cost efficient as you can while meeting your basic needs. *Then*, put that money you saved from not building a crazy setup into getting a great high end battery.

Curious though pengyou, *how much* torque do you need? A higher wound hub motor will put out a huge amount of pull at 48v, my 408 for instance will dominate everything I can get up with my lowest gears on my best climbing mountain bike, but faster.. If you need more than that, the only other hub option would be moving up to a higher wound series 5 Phoenix motor, or getting a high torque geared motor.

The Stokemonkey is probably the absolute king of torque output, but pricey, and unfortunately right now I think they're not taking new orders.

pengyou

How much torque? Good question...my original reason for looking into gears and a chain driven motor setup was to squeeze more efficiency out of the battery-motor combo that I was using. I am not an engineer but it just doesn't make sense to me to have one hub motor driving the wheel of a bicycle - like having one gear in a car. I am hoping to get more miles per charge with a decent set of gears.

Abneycat

Well, what you'll find is that the answer is yes and no. A fixed hub motor such as a Crystalyte or Wilderness Energy will have a peak efficiency range, generally varying from hub to hub (picking the right one for your particular task will naturally give you the greatest efficiency benefit). Also, increasing the amp limit on your controller will increase the efficiency range of your hub motor. A properly chosen hub motor with a properly chosen controller will provide a good peak efficiency range for most users.

That said however, geared motors provide the benefit of allowing for various torque/speed combinations, which inherently increases your peak efficiency range by quite a bit, making the geared motor a more versatile choice for being able to remain in its best for a wider variety of situations.

If you're wanting more miles per charge, the biggest gains you can get will probably come from better tires, slower riding, and pedaling when out of your motor's best range.

Lock

If you had front and rear hub motors how would you control them? Would a standard controller do the trick? How would you turn one off when you didn't want it? Must they be the same wattage? If I had a motor fwd and back, it'd only be because they are for two different purposes... Folks tap about dual windings, but two common off-shelf motors may be a cheaper solution? Dual controllers toggled from one accelerator thumb/grip whatever control, so only one employed at a time.

I expect to use front drive only in the future. Chosen for torque and not top speed, and no opportunities for "wheelies" ever.

tks

loCK
human-electric hybrid

geebee

If you live in steep terrain a geared drive will help alot as compared to a single speed hub which will give either a high speed or great climbing but not both, especially so if kept remotely legal. The other great plus is the reduced current consumption on steep hills, the steeper the greater the benefits.

FWD has some great advantages but also some problems, ie. incorrect power application on a slippery surface whilst cornering can be entertaining.

cerewa

geebee

But when was the last time you saw a train climbing a 20~30% slope?

kcweb

If you have a Crystalyte motor, you can use a dual motor controller. You can find it here:

http://www.youtube.com/watch?v=wnwWpjXh5jc

and purchase here:

http://66.216.117.91/Crystalyte_Dual_Motor_controller_p/us-crystal-c7220dm.htm

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