Tuesday, October 18, 2016

Cycle Tracter

the secret to a cycle tractor is the gear reduction

With 450lb to 550lbs total combined weight, a cargo bike needs very low gears.

There are a lot of young males that think gears waste energy. If you are racing that maybe true. But for hill climbing or stop-n-go city driving that is simply not the case. If you are obsessed with speed, go to a mental hospital; you need help before you kill yourself.

As you can see from this diagram low gears use less energy. If you are restricting your motor to a single gear, it should be as low as needed for your steepest hill and total combined weight. The brushless motor will still move you faster than that on flat land if it goes up to 1500 watts for a few minutes. So you will need a programmable controller and a speed sensor if you want to make it perfectly legal in our state. And you should use double padded hydraulic disc brakes simply because stopping 450-550lbs at 20mph isn’t easy!!!

Then tell your state law makers to change the e-bike laws so it reads "continuous output power" instead of “maximum output power”. Which would give you the room for peak bursts up hills.

 A 6:1 ratio can be done in a single stage reduction. But a rim pulley may needed, and maybe even make some splash guards to help keep the road grit out of it. In fact if someone wanted to do it right they could just use a single gear hub like in this thread that used a front motorcycle hub to hold the sprocket: https://endless-sphere.com/forums/viewtopic.php?f=28&t=59122&start=75&hilit=skeetab

Even mid-drive kits need lower gearing for this kind of application.


It is nearly impossible to use a single stage reduction with any motor for this application. For 400lbs it would be easier. At 1100rpm it could be done with an 8:1 reduction, but would still need a little more power if you wanted to drive more than 10 to 11 mph up a 9% grade. Well a faster more powerful motor and build a two stage reduction even if it is more expensive. 


You could use a motor that is rated for a high wattage at a high voltage like 48 then run it at a lower voltage like 36 and it should have a slower RPM. This will create higher amps per volt so the wires need to be thick enough to not over heat. Too bad motor manufacturers don't publish performance graphs at different voltages.

But the easiest way to get enough power yet not too much is just to use a good programmable controller that will keep that large motor down to a reasonable wattage and RPM. You could even find a used motor that would work; just remember that it is very easy to kill your self on a wimpy over powered vehicle with wimpy under powered brakes. I have known at least three people to die because of too much speed on their cycles

If you could add more wire to the motor it would run slower. Howto add more turns to a motor.


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.
You may need to get some one to measure the RPMs at the wattage you need just to build that low gear correctly. Or find it on the motor spreadsheet or graph. The right gear reduction will save energy and keep the motor from overheating.

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.
Required output power is pretty much a linear increase to speed or grade. So at 10 MPH on 5% or 5MPH at 10% just double the watts required. But here is where it gets challenging; how many watts in to get the required output depends on efficiency which also depends on the speed.

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.
Trouble is at that speed it won't shed heat fast enough for sustained rides, and you'll be building heat at a rate of about 300 watts. A simple rule to convert that to thermal rise is every watt-hour of heating will raise 1 Lb about 3° F. So that begs the question of how tall is the hill?

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.

pedal assisted power drive

The crank should drive the motor, if the motor drives the crank your top speed can be much faster than anything legal.

If you can find a motorcycle sprocket adapter that will fit the free-hub body it would be easy to use two chain drives on the cassette side.

  • controller:
  • Sprocket adapter (may need a longer axle or shorter hub to fit)
  • #35 chain
  • Large motorcycle sprocket (to fit the chain)
  • Motor:
  • Throttle:
  • Battery (the most expensive part)
  • Cycle-Analyst power meter
You could use regenerative braking in the rear for your in-place of a break, if you have a good break in the front.

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.

It would be very easy to add sprockets to the right side if you could find an adapter for a light motorcycle sprocket for #35 chain to fit onto a free-hub body behind a 6 or 7speed cassette. Then a ratcheting one-way bearing on the motor, so you don't have to crank the motor when it is off.

And thinking about a greasy chain splashing road crud on a disc rotor, it would be best to use only a belt drive on the left side.

Regenerative braking:

Direct 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.

Setting a controller for climbing steep hills with cargo:

Best 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.

Choosing a battery

Try to carry enough battery to keep your discharge rate under 2c.
For 10 amp hour size, that would be a 20 amp controller and about 700 watts.

To keep your self from being ripped off when choosing a battery please read this article!

Lead acid 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.

Belt or Sprocket Adapters ???

BIG BLOCK alternative Motor (for a larger motor)

NOTE: The motor wires are color for color on the Lyen controller (post 12 on page 2 of this thread: https://endless-sphere.com/forums/viewtopic.php?f=28&t=59122&start=25)


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. 

sprocket calculator


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