Friday, October 29, 2010

Motor-pedal hybrid design

Can these things climb a steep hill (like 9% grades) with cargo, (like children)?

You don't really need pedals if your moving over 450lbs, just a big motor.

Hub motors are the most efficient but only if you do not have steep hills to climb at a speed limit of 20 mph. Two geared hub motors would help. But a two stage gear reduction is best for a pedal car.

This machine does not have pedals because it is better to classify these as motor cycles and use motor cycle brakes.

 First stage gear reduction:

Motor-pedal hybrid design

If you live with steep hills and want to drive a more than the usual bicycle-weight up them, you really need to put some thought into how to motorize the machine. Some people think that all e bikes do not last long, because most of them are designed for light weight duty on virtually flat land.

Hub motors are the most efficient, but not for this scenario. Climbing hills at legal speeds up steep hills wit only one gear, is hard on a motor and controller. Even if electric motors do have a much wider range of ability than gasoline motors.

So most people build for momentum, that takes calculation. Or just a reasonably low gear on the drive wheel, and possibly a larger than legal motor.

The federal government says that one horsepower should be the legal limit, but in the state of Washington 1.2 hp is OK. Most people I know, chant the phrase “the cops don't care”. But when I asked the cops in Seattle they told me how they do care, and how they deal with it.

In Europe the cops are allowed to have road blocks and do any thing they want to keep the people from using a motor bigger than one-third horse power. That is almost impossible to drive even one person, with out cargo, up a steep hill.

It is possible to use more than one motor, see the white trike car above with two or three hub motors.

Geared hub motors are available in 5-1 gear reductions or less. When I calculated for a 30 mile range velomobile, I had to use a 6-1 gear reduction because lead acid batteries are very heavy. Better to use lithium. The price works out to be the same as lead acid over the life of the battery.

If it is true that electric motors must spin near peak efficiency RPM to get full horse power
and that you need a very large gear reduction to allow the motor to spin that fast and still keep the vehicle down to a legal speed. Then most e-bikes are illegal.

For high torque at low speeds you'll need a motor and controller that can allow high amps at low speed. If you get a programmable controller you can limit the power to legal levels.Peak efficiency
Series wound motors have a peak efficiency rpm, when powered past that rpm the efficiency goes down sharply and they start stressing out ["A brushed series wound motor becomes extremely hot with as little as 10% over gearing"]. With a single gear configuration it is easy to know what the motor’s RPM is by the speed, if you know what that peak efficiency speed is. An ammeter with a volt meter is even more can is a good replacement for a tachometer in an electric drive train.

You might need something like this to get a continuous true 1 HP at slow speeds:
This is the motor to use for a 500 lb vehicle:
But you may have to gear it down to 15 mph or even less.
I think that the Mars 909 would be better, but it's a bit past the legal limit.
Bicycle drive chains are not strong enough for a heavy machine like these velocipedes I tore two bicycle chains with just my unassisted legs on my mountain bike last year. So motor cycle chains or automotive belts are best unless you can keep from accelerating hard enough to destroy the a bicycle chain.

The reason not to use the bicycle gears with a motor for heavy utility machines, is that the motor can not give you much power at the gear reduction and speed you must have for cranking speeds. And if you use a large enough motor it will over power your drive chain, unless it is a very heavy duty old style chain. And a heavy duty one to three speed rear gear hub. Even then try not to do any hard starting, like drag racing.Hub motors cannot use 12 volts because the thickness of the wire needed for the higher current will not fit through the axle; that means you will not get as much power at a low speed.

Most electric motors can’t be run on 12 volts because the windings can’t handle the
increased amperage of the lower voltage.

Geared hub motors use three large planetary gears that waste enough energy to make a single gear reduction worth the extra thought.

Brushles motors do not over heat as easily as series wound brushed motors and they have a wider range of peak efficiency, ie: a wider range of speed variance under stress. And they are approximately 5% more efficient.

Gearless brushless hub motors were developed for light weight solar powered vehicles that do not have the limitation of speed limits, or excessive weight.

I just wish I could find a chart telling exactly what they can do in terms of weight, gradient, and speed.

The ‘Cycle Analyst’ maybe able to control the speed with out eliminating the slow speed amps. But there may still be a chance you could burn out your power system if you run too many amps through it at too low of a speed. A heat sensor could be good.

Heavy vehicles on steep hills need batteries with a high discharge rate.


Trapezoidal or square drive Timing Belts??

A thin section belt, as the pitch change at the periphery would be quite small

This should be ratcheting so it will eliminate the drag of the motor when just pedaling 

This lack of gear reduction may need a large motor that will have enough power at slow rpms.

wheel speed formulas: wheel pulley / drive pulley = ratio......then 
motor RPM / ratio x 60 x tire circumference / 12 / 5280 = MPH 

Trike stability

Delta trikes and quads need a differential to use a single stage reduction; unless you can live with a lopsided traction drive (but that can push the nose of a delta trike to one side on wet hills).

Two-wheel positive traction can be had with a jack shaft, but will need a two-stage reduction.Delta trikes also have a tendency to roll over on a fast turn. The only thing that can be done for that is to weight down the rear wheels and lower the seat, then slow down.

A tadpole trike can spin out of control if the rear wheel is too close to the front and may be forced into a spin by too much weight on the rear; don’t use slick tires. But if the rear wheel is farther back it will need more weight to keep a grip on the road in an emergency stop-turn. In line tandem tadpole trikes probably will not have this problem. But the front wheels of heavy tadpole trikes should be built with the spokes all the same length to handle the lateral forces.

Low seats help keep trikes from flipping over, but they could still use a crash cage even if just to climb out of the seat.

Wheels should have at least 36 14-gauge spokes, 20" wheels with box wall rims are stronger than big wheels, although there have been good results from using the new tubular rims with only 32 spokes for down hill racers (jumping off cliffs).

Tires are a problem for this much weight. High pressure tires are essential but will give you a rough ride. I have a lot of expensive tires split down the middle. Maybe Moped tires?

Brakes are the most important thing

Only hydraulic disc brakes can be synchronized perfectly, but a double lever is not available, except for the Magura BIG brakes: But you will still need a third brake on the rear wheel with extra large rotors.

Drum brakes modulate better and give you more control over stopping than cable pull disc brakes, but are available only in cable pull and are no good in the rain.

If you insist on using a bigger motor than 1hp like the mars 909 ( the name has changed)

with out adequate gear reduction you will need to use motorcycle brakes, lights and tires.

Actually I don't know if it is possible to build one of these that is perfectly legal unless you can keep the weight (450lbs?) and speed down to about so the brakes work like they should.

gear reduction formula:

3000rpm x (3"/9") x (3"/12") x 2074.71 circumference x 60minutes x .621504 mi/km= 19.3mph

These should be built as a Moped.

'Build your own electric motorcycle' by Carl Vogal. I think people who lust for speed should be building electric motorcycles.

When the center of weight is so far forward, it is possible to drop your feet, and have them dragged under the front axial. It is much safer  to have the crank behind the front wheels.

Note that the crank should be behind the front wheels. But the front wheels should also be wider apart.

This one could use three hub motors

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