Friday, October 29, 2010

Motor-pedal hybrid design




More about the laws http://commutercycling.blogspot.com/2011/01/blog-post_2907.html

http://ledreview.info/2013/printers-terratrike-velomobile-skinning-is-completed/
http://bicycledesign.net/2015/02/a-collection-of-velomobile-links-part-1/








How to power a heavy Velomobile or Cycle-truck.


Velomobiles can get a get an efficiency of 40 miles to 85 miles per kilo watt hour of electricity. While it is easy to build a Vehicle light enough to get the really high mileage number at a slow speed on flat land, try thinking about how to power one that will hold two adults and 80lbs of cargo. Or a cycle-truck that will not be heavier than 600lbs (total combined weight) that will be driven up a 9% grade. We have worse hills but they are avoidable. If you think that is bad do the numbers on the new electric cars! 3.7 per kWh is high mileage.



I think the main reason that there is not much knowledge about this kind of vehicle is no one knows how to build one.



Most people build only for speed, unfortunately if your in a wreck and you get blamed for it the cops have to send your vehicle to be checked out by a technician, to make sure it cannot be driven faster than the speed limit for this kind of vehicle. So your best bet is to have it registered as a moped, or a motor-cycle. Using only one motor you could gear the motor down to the 30 mph limit, if it is still powerful enough to climb your steepest hills.




An option you might consider is using a multiple Kw capable motor and using a programmable controller to keep the total power running through the motor within legal limits but still allow multiplying up the phase amps for torque when hill climbing in the motors lower end.

For example lets say you used a 4.5-Kw rated 72V high power scooter motor. Normally you would use a controller with such a motor that would allow for motor phase amps to reach nearly 200-Amps with a battery side Amp limit of 65-Amps or so. You would end up with an electric motorcycle that could really move.

For a lower total power build, within e-bike legal limits, you still use the same motor and still use a large powerful controller that can handle phase amp multiplication. One that goes all the way up to the that 200-Amp level when the motor gets bogged down when climbing a hill, to get the full torque. But if you program in a much lower Amp limit on the battery side, thus ensuring you stay within legal total power limits, you still get the bottom end torque. Also you don't need a great big battery that can handle sustained 65-Amps pull on the battery end.

My state the legal power limit, for it to still be a Moped bicycle by the letter of the law is "2-brake-horsepower maximum" which is equivalent to 1.49-Kw physical output power. "Brake-horsepower" defines a motors physical output power not the electric power input. Thus in my situation I would examine the motors performance graphs and figure out what battery-side amp limit I should program in, to ensure that I stayed within that limit (knowing the general performance curves of such motors on a 72V system that would probably end up being about a 25-to-30 Amp limit on the battery side).

Basically use a much bigger motor and controller and just dial down the Amp limit on the battery side and thus tapper off the middle to the top band of the motors performance but still keep all, or nearly all, of the high torque capability of the bigger motor on its bottom end.



You do not want not to add speed to a 600lb vehicle. One of these motors can pop a bicycle drive chain easily. You will need a “Cycle Annalist” to help control the vehicle. And a controller that will read the Cycle Annalist. And at 600lbs with a speed of 30 mph, you will probably need hydraulic disc brakes. And I do not mean the small kind made for simple bicycles.

I calculated the power it would take to climb some our steep hills. There are other calculators on the internet, but they use metric.



{quotes from endless sphere forum}
Efficiency pretty much doesn't change down to 80% max speed, may fall off some at 60% max, and may for certain motors fall off up to 10% at 30% max speed. That means if the bike can go 25 mph it may at most take a 10% efficiency hit if ridden at 7.5 mph (without pedaling). It also means that if the bike can go 40mph, it will take about a 5% efficiency hit if ridden at 20 mph.  36V 20A at 10 kph. Efficiency about 42%. Switch to 11V custom battery. Now at 10 kph, efficiency is about 72%.

Lower voltage systems are safer, have easier BMS requirements (less channels), less complexity, more compatibility (with DC converters and other components), and easier on electrical components

use this simulator to figure it out:  http://www.ebikes.ca/tools/simulator.html


e-bike motors:

converting a hub motor to mid drive motor:


This machine does not have pedals because it is better to classify these as motor cycles and use motor cycle brakes.
http://www.thecartimes.com/plug-in-electric-tricycle-piet-plugs-away-green-comfort/


http://wildnaturesolutions.com/
Links to Enineering tool box. com:

Gear calculations

Bicycle gears


Pulley diameters and speed




























 First stage gear reduction:
















regenerative braking 


Is it worth the effort and expense to put regenerative braking on an electric bicycle?” For grades
steeper than 4.1%, we would need LiFePO4 batteries to recover all the energy. There is energy loss associated with adding regenerative braking and there is just no way to regenerate enough power to make it worth the expense and effort. It would be much more sensible to put money into an aerodynamic fairing, even on a cargo bike. Velomobiles are made to cut the wind resistance that really slows a vehicle down, starting at 25mph. And Cars are a lot more heavy than a velmobile or cargo bike.








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 with 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 a little less than lead acid over the life of the battery.


geared hub motor

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 amperage at slow hill climbing speed. If you get a programmable controller you can limit the power to legal levels.


 Some motors have a lot more torque when run on 24 volts rather than 48 volts, So for a heavy vehicle and steep hills there could be an advantage to run it at a low voltage setting
brushless motors that are big enough for 600 lbs
http://www.cloudelectric.com/category-s/332.htm



These are best for 400 lb total combined weight 


The unloaded RPM for the 800W is 1333 versus ~1150 for the 650W and 500W motors though, so that might be the difference. Less torque, but higher speed.





Most electric motor systems will have a power/torque curve which looks similar to this:

You then ask two questions:
Is acceleration in constant torque region enough for every use of the vehicle?
Is constant power region and max rpm enough to give an adequate top speed?

If the answer to both questions are yes, then a 1 gear transmission is enough. Otherwise, the vehicle can benefit from gears. Then you get to choose whether to use a gearbox or to change the electrical system.


“In n
ormal mode, or the constant torque region, the motor exerts constant torque (rated torque) over the entire speed range until the rated speed is reached. Once past the rated RPM speed of the motor, the torque will decrease proportionally with speed, resulting in a constant power (rated power) output. The constant power region eventually degrades at high speeds, in which the torque decreases proportionally with the square of the speed.”
Conclusiveproof gearboxes are awesome.


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.                          




http://www.ebikes.ca/drainbrain.shtml








If 3 to 7 years life span is long for a big hub motor, then forget them.
(For Life expectancy, hub motors could work 5000 hrs without damage in Lab.
In real life it depends on the motor's usage (e.g. hitting bumps and water getting in).

You can make a good heavy-duty motor like the brushed Mars 909 last twenty years if you do not over power them with a cheap controller.





  One other thing to consider is that if your motor nameplate says 1200W, that's the electric power it  draws. Its actual output will be less, possibly considerably less depending on the motor design. 



How to calculate a fixed gear 



 First measure the average grade of your worst hill. Use a carpenter level and a metric or 'tenths of inch' ruler.
And divide the span by the rise to get the percent of grade.

Decide what the total combined weight of your machine will be. Include every thing!
Then use this calculator to find how much energy it takes to climb your worst hill, as a 'streamlined trike'.

Find a gear ratio that will bring the drive wheel RPM down close to the legal speed limit (or what ever you can live with) when at the wattage you need to climb the nasty hills. See graphs provided by manufacturer. (this motor should have enough torque for any hill)
Decide what you think maybe a good sized pulley for the motor, you may have to rethink the size later. Divide the diameter into the size of a larger pulley on the drive wheel.

use this simulator to figure it out:  http://www.ebikes.ca/tools/simulator.html




When using a rim sheave the belt may slip! Especially in wet weather! Unless you add something inside the rim like matte textured electrical tape or ridges some how.





    To use a Gates power grip belt 8mm pitch GT3 down load the manual and rack your own brains to find the parts to fit together to get a close ratio to slow your drive-wheel down far enough! It will be easier to find a large belt pulley for a 20” wheel than any larger wheel. 
















 Look for a 

"One-Way Locking  Bearing" 

to make a ratcheting pulley.


"One-Way Locking  Bearing" 



Trapezoidal or square drive Timing Belts??

A thin section belt my be the best,where 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 




Use gates power grip GT3 8mm pitch
get the pulley at the same time your finding the length you need.








http://www.volksrods.com/forum/showthread.php?t=37725 
















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.http://commutercycling.blogspot.com/2007/10/trike-wheels.html

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?


http://commutercycling.blogspot.com/2007/10/tire-liners-expose.html


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: http://www.greenspeed.com.au/magura.html

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.





Moped laws of Washington state says that you can't have more than
 2 Brake Horsepower




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.




'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

No comments: