|the secret to a cycle tractor is the gear reduction|
With 450lb to 550lbs total combined weight, a cargo bike needs very low gears.
The simplest way to motorize a cargo bike is to buy a direct drive hubmotor rated for 1500 watts and above. Then hook up a programmable controller to it and control the motor down to something close to legal wattage, like 1400 watts. Then If you think the cops are going to test your vehicle if some one runs in to you, just put a label on the motor stating the legal wattage, like 750w; federal law is the easiest to claim ignorance on.
Geared hub-motors are much more expensive than 'direct drive'. And external belt drives like this will outlast any chain drive system.
Starting with efficiency, the frequency of pole switching events has the largest effect at lower speeds. Virtual rotor speed. You can get an idea of that about halfway down in this article:http://www.triketech.com/Drivetrain/PowerAssist/HPV-MAC-V2.html
The Grin simulator is an exceptional tool, when used for comparisons but in the real world one finds their usage often deviates from what they were inputting.
If your looking for hill-boosts. Here are a few numbers to start with:
5MPH on a 5% grade will require 274 watts of output just to lift. At that speed the efficiency will be much higher for a geared vs direct drive nearly double. Less heat to shed.
Limits. You have a 36V battery that I would assume (LiFePO4) capable of 30A continuous (check, including BMS). That allows a budget of about 1080 watts. If you pedal at about 30-40 watts (overcoming rolling/areo drag) at 7 MPH climbing a 10% grade the efficiency of the MAC12T will be in the 68-71% range; that provides about 750 watts to the ground, and 330 watts to heat. Most typical DD motors will be down in the 50% range and below in the real world.
Lets work with 100 foot climb increments. 7 MPH @10% will take 97 seconds. 97/3600 = .027 hours, multiply by 300 watts = 8.1 watt-hours = 24 BTU. The stator assembly weighs about 5 Lbs, so 24/5 = about 5° F.
|veloci front hub w/ two disc mounts|
|sprocket bolted on front hub used on rear|
A #35 chain to the left hand side of the drive wheel is better than a BMX chain. The hard part is figuring out how to mount a large sprocket on the hub and still keep your disc brake.
I think it would be easier to use a belt drive with a large rim pulley on the drive wheel than any kind of drive chain, unless it has a two stage reduction. I could not find a sprocket large enough for a single reduction. But a 12inch child's bike rim makes a good enough pulley for a belt. Then a 1.5” belt pulley on the motor would be close to an 8:1 ratio.
drive hub-motors even just for bicycle use are not a very good option
for true cargo hauling ability at least in my experience. For a cargo
hauling a manual transmission with manual clutch that allows
aggressive downshifting regen braking (and also downshifting for
getting those big loads moving or dragging them up hills) is a very
good idea. Why do you think the big 18+ wheel tractor trailer rigs
still use manual clutch transmissions? In-fact due to the greater
downshifting regen braking ability of electric motors compared to IC
compression braking the argument for this kind of drive system is
even stronger for heavy cargo hauling.
a controller for climbing steep hills with cargo:
to probably take a Kelly controller and set the output motor phase
end amp limits to the exact same as the battery input side amp limit.
That will give you nearly constant stable torque, if that's too low
to do the controlled front wheel pop up you desire on take-off then
slowly up the output motor phase end amps limit while leaving the
battery input side amp limit the same which in each step will
increase the bottom end torque slightly and just keep upping it in
increments a little at a time until you get the level of bottom end
torque that gives you what you want.
to carry enough battery to keep your discharge rate under 2c.
10 amp hour size, that would be a 20 amp controller and about 700
keep your self from being ripped off when choosing a battery please
read this article!
batterys are now costing about the same as lithium-ion per watt-hour
and life expectancy. I hope that lead acid will eventually cost much
more than the light weight cells; even if they do need to go to the
moon to get the lithium materials.
BIG BLOCK alternative Motor (for a larger motor)
|sprocket adapter for free wheel hub|
Best thing to do is to use a large sprocket like this one and just bolt it onto a large sprocket from a used cassette, or possibly two. then use a smaller cassete for the leg powered chain.
/ how to motorize a big vehicle/ Hub Motors / How much power do you really need?