Introduction: Engineering a Power System for Heavy Cycle-trucks and Velomobiles

Picture of Engineering a Power System for Heavy Cycle-trucks and Velomobiles

Downsizing will be the only thing that will save us from our technlogys.

Heavy utility cycles will become a very large part of transportation as people wake up to the reality of climate change. It is not easy to understand how to provide enough low-speed torque thrust that is needed to climb steep hills at legal speeds. Bigger motors are not the best solution. Proper gear to power matching is much more efficient and economical, especially in terms of mileage.

Many people confuse torque with power. They are different terms. Motors can have high torque-thrust at slow hill climbing speed, or low torque-thrust at a high top speed and yet have similar power output.

Step 1: The Simplest Way to Motorize a Cargo Bike for Steep Terrain

Picture of The Simplest Way to Motorize a Cargo Bike for Steep Terrain

If you can understand how motors need lower gears to climb steep hills of the pacific northwest, save energy and get better mileage. Just use a geared hub motor built into a 20” wheel. On a bicycle that will operate with a 20 inch drive wheel. And if you need more info than that just ask Lunacycles about which 5 to1 geared hubmotor to buy. You will still need to know the grade and total combined weight that you want to drive up it.

Most people will not even think about trying to understand these graphs no matter how easily understandable I make it. So all I can say is “use more power than you need”; Buy a 1500watt motor. Most motors have the peak performance RPM and watt rating on the label.

Geared motors are not best for more than 350watts, use a direct drive hub motor. Mount it off-set from the wheel hub. A slow motor like a hub motor will keep you from needing a two or three stage reduction.

The best 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) and mount it behind the seat post, in-front of the rear tire. Or of course you can use a motor that needs to be run at a power output that can overheat if stressed too long. 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 steep terrain unless their power systems are custom engineered.

Small fast motors would be the best, but they require two or three stage gear reductions. And a two gear system would be really nice:

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 ( 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' and can have problems with 450 to 550lbs. External belt drives like this will outlast any chain drive system. ( And motorcycle chain-drives will outlast any bicycle chain drive.

We need thousands of small shops working on this to replace all the gas gulping cars before it is way too late, fossil fuels are on their way out. Start a new economy from the ground up!

Do the graph with the load line first to choose the right wheel size (gear reduction)

Step 2: Finding a Motor That Will Climb Your Worst Hills.

Picture of 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.

The graphs above:

A. This is proof that a higher gear (smaller ratio contrast) will use more power than a lower gear, to climb the same hill at the same speed.

B. Proof that a lower gear (larger ratio reduction) runs cooler and will climb a steeper hill at the same speed as the higher gear.

C. Shows that if the gear ratio is right, there is no exesive heat build up on the same steep grade, even with more wattage. And it is possible to climb an even steeper hill when needed.

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.

Gear Reduction Ratio

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.

If you want to calculate the most effective gear with math try this:

Here's an alternate explanation:

The black Load Line shows the power required to propel the configured bike at any speed. This has nothing to do with the simulator - it reflects the same results you get from any standard bike speed calculator - basic physics - nothing to do with motors. This is all about aerodynamic drag, rolling coefficient, grade, etc.

The red line is the mechanical power the motor can deliver at any speed where speed varies according to load not throttle. This is based on dynamo data and Justin's modeling - this is the 'simulation' part and has nothing to do with drag, grade, etc.

The intersection of these two lines is the point where the power to propel the bike is exactly equal to the power produced by the motor. This indicates the terminal speed for that bike configuration and load. This is simply a graphic solution to two separate sets of power equations (i.e. it could be done algebraically - the graphic solution is equally valid...)

This means that if you want know how much power it takes to push your bike to 35mph, you just turn off all the lines except the Load Line, configure the bike, then look at the power at 35mph... This is the amount of power required regardless of the motor or drive system. It's only when you play this curve against a specific motor that you get into the terminal speed, etc where the specifics of that motor/battery/controller can be balanced against the requirements of the bike/grade/etc.

Motor graph simulator: (use a new browser)

Power needed calculator:

Gear ratio calculaotor:

Step 3: ​Choose the Best Way to Power-assist Your Human Powered Hybrid Vehicle:

Picture of ​Choose the Best Way to Power-assist Your Human Powered Hybrid Vehicle:

Mid-Drives are very good for low wattage motors. But over 500 watts can put too much stress on bicycle drive chains, especially if it is a narrow chain for more than 7 speeds. BMX single speed chains are the best if you don't want to use a motorcycle chain on the other side of the drive wheel. And slow acceleration is easier on the chain.

Direct drive hub-motors are set at a very high gear, therefore are not good for hard acceleration like in stop-n-go city driving. Even if they are Brushless motors and can be pushed past the peak efficiency wattage for a few minutes, they need more ventilation.

Geared hub-motors are not available in more than a 1:5 gear reduction. Hub-motors can obtain full thrust at a slower speed than most other motors. Most hub-motors do not ventilate well, so they have heat problems when using high amperage while climbing hills in a gear that is too high.

High speed high voltage motors are better than slower motors because they do not build up so much heat. And are more efficient than hub motors, even with the large amount of gear reduction needed to produce the amount of thrust needed.

Two speed transmissions are all the gear ranges needed for electric motors, unless you want a very wide range of speed, or if your using a high speed motor that does not have enough low speed thrust. ie: your government may not allow powerful enough motors for your needs. If you are allowed all the power you will need, but just need to cut it off at the legal speed, that can be done with the controller. If you live in very steep hill country and you're going to be moving a lott more weight, you may want three gears.

Two motors in tandem can pump-up the output thrust without increasing the overall speed that is set by the fixed gear ratio. A controller for each motor is needed but then you can program them to power-up the extra motors when needed. And both controllers can be wired into one accelerator.

What are the advantages? Electric motors loose thrust ability when climbing hills at a slow speed; if you want your high speed gear-ratio to be set at about 20mph and you need a 10mph gear ratio to get enough thrust to climb your hill with only one motor, a second or third should provide enough thrust at 20mph without having to use a larger motor. The bigger motor would take more amperage to keep running at a high speed when cruising on flatter land, where the extra power is not needed. Also motors made for high speed are more efficient than slow speed motors; less energy is turned into heat.

It would be possible to use a gearless hub motor for a cruising gear with a mid-mounted motor with a large gear reduction for hill climbing.

Two Separate Reduction Ratios

I like the idea of using two motors separately. One with a large gear ratio reduction and the other with a higher speed reduction. Then the controllers set to turn on the slower gear reduction when needed and the other to turn off. Making it a two speed machine with the same legal wattage.

Vector Control (field oriented control) is a better way to make motors produce more thrust at lower and higher speeds than using gears. With controllers having more computing power now, they can control a motor much better than ever before. It requires a three-phase AC motor and a more expensive controller. These would be very good for a motorcycle that needs a wider range of torque-thrust than a simple electric bicycle.

Increasing the number of phases above three allows the stator MMF's to be shaped so that the motor produces significantly greater torque.

E-bike laws should be changed to reflect the gear speed so that you can still have enough power to climb your worst hills. i.e. Washington state allows only about 1000 watts for a power assisted bicycle and 1500 watts for a moped. Well if you want to move 600lbs (272 kg) up an 8% grade you are going to need a gear ratio that will drive at about 12mph (19 kph) at the r.p.m. that your motor will produce at that 1500 watts.

One reason the laws don't let you have more than “a given power output”, is because even if you have a controller set to turn off at a given speed, the sensor can be by-passed. And it is very unlikely that a law restricting the bike to the use of controllers that do not work without speed sensors, will be functional in the USA.

Some states require a torque sensor on the cranks. This is probably the only way to restrict the speed that cannot be bypassed easily. But this would also need to be examined by an “engineer”.

Step 4: ​Brakes Are the Most Important Part.

Picture of ​Brakes Are the Most Important Part.

If they are not strong enough to over power the motor, you can get into worse trouble than you want. Double cylinder hydraulic disc brakes should be used if you are going to be moving 600-800lbs (272-362 kg) faster than walking speeds, or down a steep hill.

Step 5: Leverage

Picture of Leverage

There are a lot of people that think gears waste enegy. Boy are they wrong!

Gears are force multipliers

How much power do you really need

The myth of ebike wattage

Vector control: “field oriented control of permanent magnet motors” on youtube:

This cannot add horse power, it can only put it where you need it, like at the slow end so that you have more thrust when starting off from a stop light or when hill climbing with cargo.

A 2 speed gear box:

Choosing a battery:

Read more on my non-profit blog: Utility Cycling Technology

motor pedal hybrid design

fixed gear drives

My facebook page about utility cycling technology:


How gears work:

Hub Motors for Cargo bikes?

Step 6: Excellent Examples

Picture of Excellent Examples

Step 7: State E-bike Laws Must Change!

Picture of  State E-bike Laws Must Change!

Washington state e-bike laws are not adequate for heavy duty cargo bicycles.

The maximum power allowed for a motorized bicycle is 1500 watts at the drive axle. The motor will have to draw more than that.

1200-1500 watts will move 4500lbs (total combined weight) up an 9% grade at about 12 to 13mph if using the right gear. Unfortunately most people think they need as much speed as they can get. So if a moped bike had a gear box with at least two gears, there would not be a problem.

But if you want to use a fixed gear drive the 13mph is the maximum speed the vehicle would drive at. So the laws should reflect the amount of gear reduction your vehicle has; ie: for 20mph you need about 2200 watts to move that 600lbs up an 8% grade.

The wide torque band of electric motors, particularly the torque available at low RPM, eliminates the need for more than one gear.

Set the single fixed reduction gear at the highest speed that the available power will still be capable of driving your fully loaded vehicle up your steepest hill. Then if you still need a faster gear for less strenuous terrain, you can think about using a two speed gear box.

However it would be easier to just use a gear box, not to exceed 20 or 30mph. And have your vehicle examined for stop-ability with a total combined weight of 800lbs.

The real problem is people's insane lust for speed. They want to be able to turn their bicycles into illegal motorcycles. Well there are better ways to kill your self.

Step 8: Smaller Drive Wheels Are Like Lower Gears

Picture of Smaller Drive Wheels Are Like Lower Gears

Hub motors work much better with smaller drive wheels. Large wheels are left over from the days human power racing on the high wheel bikes that were incredably hard to ride. If you need an even smaller wheel, use a gear reduction.

Smaller drive wheels are like lower gears, that do not wear-out as fast as mid-drive kits. It is well known that driving a bicycle's chain with 750 watts or more will wear out the chain and sprockets faster than human power alone.

The only really good way to power a really heavy utility bike is with a gear reduction not using the wimpy drive chains people love ot have on their bicycles.

And using a 20inch wheel makes it easier to find that low low hill climbing gear (below 17 gear inches) needed for human power. Mountain bike gears go down to only 17 gear inches, unless you can spend much more money for a 42 toothed rear sprocket.

Or of course use a Mountain Tamer fourth chain ring. I used one on my trike and got down to less than 2mph, but that is less than walking speed, you cannot balance a bicycle at less than 3 to 5mph.

You can build one or even convert a large wheel bike to a smaller drive wheel.

Step 9: Hydraulic Drives for HPV Hybrids?

Picture of Hydraulic Drives for HPV Hybrids?

It does sound good, but is it really worth the money? Unless you can make the tanks very light weight it will be good only for large trucks, the kind that use gasoline in place of pedals power.


Tretech (author)2016-06-01

I've been working on a little idea using a hybrid electric and hydraulic drive system... it seems to fit right in line with what you're talking about here. if anybody has any information about drive by hydraulic systems please get in touch with me. my idea is to have a tandem device with electric motor and hydraulic drive where the electric motor can power the hydraulic system or the hydraulic system can assist or power the electric motor making an all-inclusive assembly. then if you have one, you can make a unicycle. 2, you can make a motorcycle. 3 or 4, you can make a trike or car. more you can make a semi / hauling / commercial type of vehicle...

I would really like to see more info on that project. Do you have a blog?

I do not. so far i've just been tinkering and planning. need metal shop and hydraulic experience/support to go further

dtpit (author)2016-06-02

Very useful information
Thank You

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