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Author Topic: Electric Trike  (Read 4407 times)
19th Century Space Pilot
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« Reply #25 on: August 20, 2008, 12:40:54 pm »

Well, the regs. say

The vehicle must not weigh more than 40 kg if a solo bicycle, or 60 kg in the case of a tandem or tricycle.
The vehicle must be fitted with pedals, by which it can be propelled.
The vehicle must not be fitted with any sort of motor other than an electric motor.
The continuous rated output of the motor must not exceed 200 watts if fitted to a solo bicycle, or 250 watts in the case of a tandem or tricycle.
The motor must not propel the vehicle when it is travelling faster than 15 mph.

That doesn't cover having more than one motor, so if I had two motors rated at 250 each...


One thing the regs. I posted there doesn't include is the age limit (14), which is the reason I'm trying to build it. I'm 14 and can't be bothered to wait around to get to 16. It's technically legal, so they'd have no grounds in prosecuting me.

One question: It said the motor must not propel the vehicle above 15mph.
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« Reply #26 on: August 20, 2008, 12:50:59 pm »

This ( http://revopower.com/ ) seems a much more practical thing, though it woudl in the Uk have to be registered etc...


I would like to see an electric version of this.
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sidecar_jon
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« Reply #27 on: August 20, 2008, 12:59:06 pm »

"continuous rated output of the motor must not exceed 200 watts ".. but the peek can be an awful lot more than that! I think all the newer systems are pedal asist too, ie it adds to your power but legally cant take over completely...
« Last Edit: August 20, 2008, 01:00:37 pm by sidecar_jon » Logged

Siliconous Skumins
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« Reply #28 on: August 20, 2008, 06:02:36 pm »


One question: It said the motor must not propel the vehicle above 15mph.

Yep, that is correct :  the motor is not able to propel the machine above the 25 km/h / 16MPH limit (so 15MPH effective speed). This is easy to do with a PM (perminant magnet) type motor, which will turn at a given speed per volt (typical would be 2500RPM at 24V) - increase the voltage, and the speed the motor runs at increases. So as long as the motor is geared down correctly, the speed will not go past the limit (unless you are pedaling at the same time...).
The more common and efficient motors used now, are brushless motors (a type of AC motor that runs on DC power via a special electronic controller), and these are usually artificially speed limited by the electronic controller to achieve the same result. Both are easy to modify for increased speed, however.

Also of note, is that the regulations changed fairly recently - now new machines (manufactured only) must only enable the motor if the pedals are turning, and also must include a motor cut-out, or gradually reduce the motor output power to zero, the closer to the 15MPH threshold. 
This is not applicable on self build machines (as stated in the new regulations), instead the motor may remain operating, but the idea is that the motor is only able to provide a max speed of 15MPH (as above), so any increase past 16MPH is largely down to your own body's input - the motor doesn't really help to go faster (even though it's still working), and if you stop pedaling, and you slow down to 15MPH again.


As I said though, this is not the 'be all, and end all' of things : when I used to ride a bike daily, I would often hit continuous speed of 20+ MPH while pedaling, and often over 30MPH on a decent downhill slope (wind resistance is the biggest problem for speeds above 15MPH anyway).  I doubt you would draw too much attention to yourself at similar speeds - unless you happen to be doing 40MPH up a 1:3 hill, without being the colour of a choked Smurf that is...  Grin

Put it this way, when I finish the controller for my trike, it should be good for about 30MPH on the flat, and a little slower up hills with pedaling. Plenty fast enough, and I doubt I will run into any problems with the boys in blue. Wink

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19th Century Space Pilot
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« Reply #29 on: August 20, 2008, 06:25:06 pm »

So in the new regulations the vehicle shouldn't exeed 15mph without pedaling? Is it okay to have the motor assisting above 15 mph?

Legal issues aside, my Dad knows someone who can build the frame.
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sidecar_jon
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« Reply #30 on: August 21, 2008, 09:17:07 am »

On speed... On a tandem i have noticed, 30mph is easily achievable, and that's the point i really notice i haven't got a helmet on! It really feels quite fast on a bicycle. 40 MPH on the flat isn't a real problem two up. But to me it simply don't feel at all safe. Specificity the brakes seem pretty useless. 15mph seems an ok speed to travel at, time to survey the country side and time to think.
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Siliconous Skumins
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« Reply #31 on: August 21, 2008, 10:51:12 am »

So in the new regulations the vehicle shouldn't exeed 15mph without pedaling?

Correct, though for DIY builds, the new regs mostly don't apply (the new regs are for manufactured vehicles sold to the general public). Neither version of the rules prevent the vehicle from traveling faster than 15MPH when pedaling - as any bike is capable of, only that motor power alone (ie no pedaling) is restricted to a max of 15MPH

Quote
Is it okay to have the motor assisting above 15 mph?

For our case with a DIY self build, yes, we are not required to prevent the motor operating past the 15MPH threshold.


The reason is that a 'permanent magnet motor' is expected to be most commonly used (because they are a little more efficient than other types of DC motor), and these have a specific RPM (revolutions per minute) per volt operating speed : say for example, 1500RPM at 12V, 2000RPM at 16V and the 'rated' speed of 2500RPM at 24V. Once this motor reaches a specific RPM at a given voltage, it will not continue to speed up, it will simply maintain that speed even if operating without any load (though it can be pulled around faster, say by pedaling a bike, but will not generate any help to do this).
These motors have strong magnets lining the motor case, called "field magnets", and these produce the magnetic 'field' that the rotating part of the motor (called the armature) pushes against to produce the turning motion. (Similar to holding two magnets with identical poles (N + N or S + S) together, they push each other away, while oposite poles pull together.)

Now we can use this fact to our advantage, we can simply (and fully legally) replace the motor with a type called a "Series wound" motor. This motor does not use field magnets, instead it uses coils of copper wire to make electromagnets called (unsuprisingly) "field coils" - and these do the same job as the magnets.....but with a difference - the field strength can change depending how hard the motor is working!  This motor does not have a top speed, the speed just keeps on increasing, but as it does, the torque (how hard it pushes) reduces the faster it turns.
The reason this happens is that electric motors actually SPEED UP when the magnetic field is reduced, but the strength of the magnetic field is what produces the torque of the motor - so it trades off one against the other : Very strong, but slow or Very fast but weak. Result is that the motor will still provide some degree of assistance past 15MPH.
These motors are not quite as efficent as the PM motor, because you waste a liitle more power in the field coils to generate the magnetic field needed to turn the motor, but it's not a huge loss.

Series wound motors are one of the most common types around, they are in most household items: vacuum cleaners, food mixers, drills, electric lawnmowers, washing machines, etc.  Becuse of their design, these motors can run on either DC (like a battery) or AC (like mains power), so a suitable motor can be scrounged up from a number of possible sources (I'm using a modified washing machine motor), washing machines, tumble dryers, large lawnmowers, garden vacuums, being among the best options. If 240V UK mains powerd devices are scavenged, you may find it necaccary to use a voltage between 48V and 72V - if higher than 50V, everything should be well electrically insulated, and waterproof to prevent any risk. 
Avoid car starter motors (also 'series' wound), these require insane amounts of power to even begin to turn withou any load (at least 30 amps no load, up to 900A under full load!!) - very inificient and will over heat quickly (they are only designed for less than 60 seconds of operation.).

SS
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19th Century Space Pilot
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« Reply #32 on: August 21, 2008, 12:18:46 pm »

Thanks, that's cleared it up a lot.

So I can scavenge the motor from any household item that has one such as a Washing Machine or a Vacuum Cleaner? Now I just have to find one that I'll be allowed to scavenge the motor from...

Now, how to set it up so I can hit a decent speed (25 mph) while pedalling with the motor on....
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Siliconous Skumins
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« Reply #33 on: August 21, 2008, 01:42:29 pm »

Thanks, that's cleared it up a lot.

So I can scavenge the motor from any household item that has one such as a Washing Machine or a Vacuum Cleaner? Now I just have to find one that I'll be allowed to scavenge the motor from...

Now, how to set it up so I can hit a decent speed (25 mph) while pedalling with the motor on....

Washing machine, yes - vacuum cleaner...probably not, usually too small (physical size) and operate at far too high a speed (typically 10,000 to 30,000 RPM). Vacuums may claim 1,400Watt motors - and while technically true - they can only operate at the wattage due to the very high speeds, and the fact that the high volume of air passing through the cleaner, is directed over the motor to cool it...otherwise it would glow RED within seconds (I have fixed a few Dyson cleaners for this reason, as the vacuum fan came loose on the motor shaft and the air stopped flowing...the motors melted!).

Also 1400 Watts of power at 240V AC, doesn't actually result in 1400 Watts of motor at DC voltages... (AC and DC resistance on the same motor, are two very different things!)  Wink

in most cases you need to look for low speed, heavy duty devices (washing machine, cement mixer, etc) - but there are a couple of exceptions: electric Garden Vacs and heavy duty hand drills. 
Garden vacs typically are rated at around 1400 - 1600 Wats, but the motor is MUCH larger than a household vacuum cleaner, and with a little extra cooling fan blowing through the motor (the case of which is designed for good airflow), should be good for around 150 - 200Watts at DC voltages around 60V or so. So two identical motors would be ideal !  I have two motors from an identical pair of Black & Decker garden vacs (though sadly one needs a new commutator due to damage - could be hard to find...), due to experiment shortly, expecting good results.

Hand drills use a high speed motor, but they are geared down. They are also available in 110V versions (for water safety), and can provide a decent amount of power.


Probably best / easier to visit a scrap yard, dump, etc, and raid a few washing machines though.

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19th Century Space Pilot
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« Reply #34 on: August 21, 2008, 08:32:57 pm »

I'll need one that is rated at 250 W continueuos power though.
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Siliconous Skumins
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« Reply #35 on: August 21, 2008, 10:19:55 pm »

I'll need one that is rated at 250 W continueuos power though.


Yup, but it's a little hard to judge what will give that power at DC current and lower voltage.  However, in general terms, the larger the motor's size and the heavier work it was used for - the more likelyhood of it giving around the right wattage (if not, then two can be used in parallel).

Washing machine motors are nice and large (and can be rewound by hand to provide the wattage you need - it's easier than you think), Tumble driers tend to be a little lower, usually around the 180 to 220W range.  With a fan blowing air through the motor, you can provide seperate power to the field coils and to the armature (the bit that spins) - in fact this how a washing machine can adjust it's speed between slow (wash) and full speed  (spin dry).
Remember I said about "field weakening", well this is it. The armature uses far more current than the field coils require, and the amount the armature uses depends on the strength of the magnetic field - and this depends on the amount of curent flowing in the field coils. So if your REDUCE the current in the field coil, the field strength weakens, and the armature draws MORE current - and thus spins faster = higher wattage.

The motor is now what's known as a "shunt wound motor". Because the field coils and armautre are no longer in series, but seperate instead, the normal resistance of the motor is now half - and this means more power can flow through the motor making it stronger (and hotter - hence the fan...).

If you do happen to find a motor that just is just a little too weak or slow (but fits perfect), I can show you how to rewind the armature by hand. It sounds complicated, but it's actually REALLY simple - and it's all just one long length of enameled wire. ( It's not too boring or a lengthy job either - couple of hours at most) Wink


Of course all that is only needed if you want to scroung a motor up for free, if you don't mind spending a little *cough* cash on a motor and controller, then  a single 250W hub motor or better a pair of 250W rated hub motors can be used (and disguised as drum brakes or similar) - this will give you 500W of power (better hill climbing ability)......but the controller may limit the top speed to 15MPH still.  You'll have to do some research on the controller before buying.


Have a read of the DIY electric bike conversions on this website - lots of good information (and hints on what NOT to do) and a good place to start:

http://www.theworkshop.ca/energy/energy.htm

Any questions, feel free to ask me. Smiley

SS
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