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:

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. But no one seems to care unless you ask the police department.

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.

 You might need something like this to get a continuous true 1 HP at slow speeds:

All power assist e-bikes are geared too high for steep hills and full cargo weight around 500lbs!
Everyone knows that hill climbing works best in a low gear, yet people still use momentum (and not enough of it) which puts more strain on the motor and batteries and the controller, so that they do not last long.

If you need to slow down you will not get the full HP of the motor unless your not climbing a hill with too much weight.

The right way to build a heavy e trike? :

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. It would be better to use a tachometer if you can get one. Actually an ammeter with a volt meter is even more important.

Cheap controllers and batteries can burn out if under sized for the maximum current flow.

Heavy vehicles on steep hills need batteries with a high discharge rate, not cheap lead acid gel batteries.

for 300LBs max

A 20” drive wheel maybe needed for a single stage reduction, or a sheave made from a wheel rim on bigger wheels.


Hub motors cannot use 12 volts because the thickness of the wire needed for the higher current will not fit through the axle, if you find one please let me know about it. 48-volt motors are not more efficient than using lower voltage. The reason that people say that high voltage is more efficient than low, is that high speed is more efficient than low speed. High voltage is like a high gear, and is not efficient when climbing hills that need a lot of torque. The slower  you climb hills the voltage lowers at the same time the amps go up. That's why Hub motors are not popular for hill climbing hills.  But they don't take much effort to apply to a bike, so that's what they are used for most of the time.

Brushles motors do not over heat as easily as series wound brushed motors and they have a wider range of peak efficiency ie: a wide range of speed variance under stress. And they are aprox. 5% more efficient (at twice the price of the mars 909 series wound, what a deal!?). So if you can find one that will work for you it may be worth the larger price.
The less the voltage the slower the but it will increase the amperage. Most electric motors can’t be run on 12 volts because the windings can’t handle the increased amperage of the lower voltage. So they may need a two-stage gear reduction.

Geared hub motors use three large expensive to replace planetary gears that waste enough energy to make a single gear reduction worth the extra thought, and low range of speed variance.

Internally geared hubs need regular maintenance and should be sealed enough to hold an oil bath.

I do believe that gearless brushless hub motors may be the best kind of motors for light weight racing bicycles. I just wish I could find a chart telling exactly what they can do in terms of 'weight-gradient-speed'.

I believe that if you do not limit the speed electronically to 20 mph, your vehicle will be illegal. And if you are in a wreck using an illegal vehicle you will get the blame even if it is not your fault.

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 would be good.

This is the motor to use 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 point.

Bicycle drive chains are not strong enough for a heavy machine like these velocipedes  I tore two bicycle chains with my unassisted legs on my mountain bike last year. So motor cycle chains or automotive belts are best unless you can just not accelerate hard enough to destroy the a bicycle chain.

A good reason to use motorcycle sprockets is that you can change the size if you need a lower gear on your regular route's worst hill.


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.

Another good book:

Electric motors and their controls : an introduction


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.

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