Introduction: The Best Way to Motorize a Heavy Human Powered Vehicle (HPV)

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

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.

There are a lot of people that think all you have to do is put an over-sized motor on their bikes. That turns it in to a deadly illegal motorcycle. A good way to die you might say. I have known too many people to kill them self's on fast bikes, even without motors, the laws are there for a reason.


Choosing a motor

My Own MtGoat CycleTruck

It took a lot of work and even more thinking but it was worth it all.

My knees had given out with severe {onerous} arduous arthritis so I couldn't wait any longer.

How to Build an Ergonomic Cycle Truck

How I motorized my CycleTruck with the help of people on EndlessSphere forum

Step 1: 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 to 1 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 1500 watt motor. Most motors have the peak performance RPM and watt rating on the label. and a 20 Watt hour battery pack.

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


A guide to multi-motor (2WD and 3WD) ebike drive systems

Understanding Everything about Hub Motor Drive Systems - Spezi 2020 Live Presentation

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

It is possible to calculate the maximum power you need for hill climbing, but it is not going to be very accurate. [Because of driving style: speed / momentum / thrust]. My motor draws up to about 1800 watts from the battery when starting hard or climbing a bit too hard. So I trained my self to make soft starts, even if just to keep from popping a wheelie and crashing [a good reason to put the center of gravity at one third of the distance between the axles].

A motor-kit with controller should be able to use a 72volt pack so you can get more wattage to the drive wheel but then you will need lower slower gears to help stay out of trouble, and high voltage gives you more overall power. But to keep it “more legal” a lower voltage would be good. Like 36volt will restrict the speed more directly than using a high voltage. But of course most people have an insane desire to move fast so they opt for the 72v rig. [get a controller set for the voltage if you want a low voltage, because a controller set for a high voltage will turn off the power higher than needed for the low voltage] without a meter to watch the wattage,amps and speed, just use a voltmeter

Be aware that hub motors waste energy as heat then have a hard time getting rid of the excess [Two hub motors work much better than only one], but then mid-drive rigs with too many sprockets use-up energy converting torque into thrust. So a single reduction “direct-drive” would be the best [use a mid-drive motor with 6 to 1 planetary gear reduction [14t sprockets on the motor to a 42t sprocket on the wheel would be almost too slow if you the planetary gears; that is why some people have been thinking about how to build a two speed retro-direct gear transmission.]

But I like the mid-drives, because I have a battery pack that is too small. So I built a front gear shifter that keeps the chain on the sprockets. There is a wobble in the crank that maybe the problem.

You can use the graphs to figure out a lot of information, but they do not have a way to test “Mid-drive” or mid mounted “direct-drives”.

So the best thing to do is to build a battery pack that is far more than you need. I have a 13 Amp hour / 704 Wh pack that I must charge up before I can make my 5 mile return trip home. I use between 40 and 50 Watt hours per mile average, some times more. What I need is a 2kWh pack or larger. Then I could not only make a longer trip but also climb the worst hills in town with no problem of heating the cells.

Then how do I figure out how much a of a pack do I really need. I just know that I need about 200 or more 18650 cells of the Samsung 29E because they have the best balance of price / capacity / and C rate. Building a pack using the highest capacity is not the best thing to do because the more densely packed cells are not able to discharge as fast as a cell that holds less, and if you do find one it will cost a lot more because that is what every one wants.

I also do not believe that using wimpy 1 ply bicycle tires are going to save much rolling resistance energy over a properly inflated 2.5” wide motorcycle tire made for more weight than you can put on any kind of bicycle tire and expect to use it for years. My rear tire [17”rim size x 22” OD] is a three ply 2.5” wide motorcycle tire made for 291lbs maximum. My front tire that has lasted about 4 or 5 years so far, is a 4ply 2.25” wide 20.5”OD 16” rim motorcycle tire mounted on a 406mm BMX rim [the only motorcycle tire that will fit on a bicycle rim] if you want to replace a car with a cycletruck it should be built as heavy duty as possible.

Some one should write an instructable about calculating the pack size needed. I am 70.6 years old and need to slow down and paint pictures.

Choosing a motor

Electric motors run fast or they will burn out, that is why they need gear reductions. I really like the ones with planetary gears in them. external gears get dirty. If you use belts they need to stay clean or they will jump off.

MOTOR POWER RATINGS (and why they are useless)



Power Lost to Electric Drive Train Inefficiency

Torque loss in helical gears: Influence of “low loss” gear design

Motor graph simulator: (use a new browser)

Power needed calculator:

Gear ratio calculator:


Two-speed gear boxes

New 2017 updates to motor simulator:

Belt Drives

Belt driven bikes are quieter and last longer. I don't like chains because they wear out too fast and then start wearing the sprockets. But even a belt should be shielded from road grit.

Step 3: ​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.

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

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

Step 7: 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

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?

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.

Step 10: The Future of Transportation

Automated cars will be everywhere in ten years. If you are stuck with a simple gasoline car, your insurance will go up drastically.