|the secret to a cycle tractor is the gear reduction|
With 450lb to 550lbs total combined weight, a cargo bike needs very low gears.
|gear down from motor to wheel at this speed.|
If you generate a graph that shows a better performance at a smaller wheel size than you have, build a gear reduction that changes the simulated wheel size to the tire size you have. Ie: a 16 inch tire is 1.62 of a 26 inch tire (1.62:1) it is ok not be exact.
Finding a motor that will climb your worst hills.
For people that want to exercise their brains, try this:
You don't need to understand the graphs, but it does help to compare motors.
Finding a motor with a graph that shows the grade needed at peak efficiency will allow you to climb steeper hills without the motor over heating.
Set the simulator's parameters and choose 'load line' to see if the grade you want to climb is close to the peak efficiency, then do the 'grade and speed' which turns off the throttle value; then Slide the dotted line (with speed on the bottom of it) back farther to see what grade and speed it can climb while keeping it near efficiency peak.
Check the speed of the wheel with the RPMs. A 12inch wheel is 2.16 of a 26 inch wheel.(2.16:1 ratio), in other words use at least a 2 to 1 ratio for a 26inch wheel if simulated with a 12 inch wheel.
If you want to calculate the most effective gear with math try this: http://commutercycling.blogspot.com/2010/09/war-for-oil.html
The simplest way to motorize a cargo bike is to buy a direct drive hubmotor (because of the narrow profile and slow rpm in the hundreds rather than the thousands), rated for at least 1300-1400 watts output near peak efficiency (see graph). It is impossible to calculate exactly what you need so expect to drive a little slower. Factory made e-bikes can't possibly fit your terrain unless their power systems are custom engineered.
Then If you think the cops are going to test your vehicle if someone runs into you, just put a label on the motor stating the legal wattage, like 750w; federal law is the easiest to claim ignorance on. In most other country's you will need a very slow gear because they don't let you have enough power to climb hills with cargo on bicycles.
Most motors need about 1200w-1500watts output to drive 450lbs up a 9% grade at a reasonable speed. The law should allow for that (http://commutercycling.blogspot.com/2011/01/blog-post_2907.html). If you think you need to climb those hills faster than 12-14mph, you need to go to a mental hospital before you damage someone.
Using hydraulic disc brakes, and speed sensors connected to you controller, and a crank sensor to turn on the motor, will make any police department happy. I consider them safety equipment.
Find the RPMs at the peak efficiency wattage on the spreadsheet or graph, to build that low gear correctly. The right gear reduction will keep the motor from overheating by increasing the efficiency and wasting less energy as heat, allowing the motor to last 20 years.
Stop-n-go city driving with a hubmotor built into a wheel is like hill climbing in the WRONG GEAR! And mid-drives are already known for wasting human-powered drive-chains under these conditions. So it is very desirable to have a second drive train. Unless you are rich enough to have a second motor instead.
Geared hub-motors are more expensive than 'direct drive'. External belt drives like this will outlast any chain drive system. (http://commutercycling.blogspot.com/2016/03/custom-belt-drive.html) And motorcycle chain-drives will outlast any bicycle chain drive.
D. To compromise for a desired speed: find the wheel size that will give you the desired legal speed, then run the dotted line back to where the red power line crosses the grade line to see the maximum grade. And forward to find the grade it can climb without overheating in the time it will take to climb the hill.
Keep the green line high if possible.
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.
|Voloci rear hub w/sprocket on one |
side disc brake rotor on the other
|this one is still available|
|sprocket bolted on electric bike hub|
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?