# Next idea...



## Woodsmith (Jun 5, 2008)

Yep, a recumbent trike would be good. I bought a KMX with a broken back for just that purpose. I rebuilt it but have temporarily misplaced a little electric bike motor I put aside for it.

If you are looking for it to be road legal then I think there are limits to the maximum continuous power output you can have, something like 200W for a 2 wheeler and 250W I think for a trike but I will check. There is no limit on maximum intermitant power though. 
It must only be able to power up to 15mph though.

Also in the UK, unlike in the EU, we can have the bike or trike powered without pedalling, that makes control easier and also more fun.

You can replace the drive train with a generator and a motor but you will get diminishing returns. However you can keep pedaling even when stationary, or when parked up at home, to charge the batteries but it will be harder work. 
Are you a keen cyclist?

Have a look at VeloVision, BHPC and my all time favorite Aero Rider.

Edit to add:
Have a look at this site http://www.kinetics.org.uk/html/uk_law.shtml
Things have changed a little since I last looked.


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## Poohstyx (Dec 22, 2010)

Hello again 

I'd heard that the limit for pedal bikes is 200w, don't know about specific limits for trikes.
How do the requirements change if you exceed the 200w limit?

Its been a few years, but I used to cycle tour and offroad (80 mile round trip with some offroad in the middle - and a pub ).
And I've always done a lot of walking, normally 10+ miles per day.

I was thinking mainly that (ignoring mechanical system losses) using a pedal driven dynamo charging system would effectively be the same as a normal chain-drive system, but without the chain.
So a bike without the complex bits 

The three advantages I see are:
a) The pedaling difficulty doesn't change no matter what the terrain.
b) Backing off the motor while pedaling downhill lets me charge from two sources.
c) If I do run out of power, a bit of roadside pedaling solves the problem.


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## Woodsmith (Jun 5, 2008)

Ahh, in that case powering an electric drive system shouldn't be a problem. I reckon it would be a good idea but you will be limited to 15mph by law.

Keeping a chain drive will allow you to keep pedalling above 15mph even though the motor would/should have stopped assisting.

If you were to go above 15mph or 250W for a trike (or tandem and 200W for a bike) then you will fall into constructions and use regulations for motor vehicles and it becomes a moped requiring better suspension and brakes, insurance, MOT, road fund licence and a helmet. Also the age limit, which won't apply to you raises from 14 to 16 or 17 depending on power and top speed and will also require a suitable driving licence.

Are you on Cycle Chat at all? I also frequent that site to chat about , well tea mainly but also bikes and cycling.


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## Poohstyx (Dec 22, 2010)

Well, I'd be limited to 15mph a the flick of a hidden switch 
Any idea about how the drivetrain for a pedal vehicle is defined?
For instance, if the battery is removed it could be argued that since there is no power storage, it is just a pedal cycle that uses a non-mechanical drive system


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## Woodsmith (Jun 5, 2008)

Yes that would be true and effective. You just need to be able to show (if you are ever stopped and checked) that the battery powered element can't push you past 15mph. That can be rigged to a speedo sensor I guess.

Also the other aspect is that the maximum continuous power is measured at the wheel not at the motor, controller or battery pack. That means that you can have motor that is rated higher to over come any drive train losses and peak at, I think, 700W.

If you join the battery Vehicle Society forum you will then have access to their electric bikes forum with much more UK relevent information and advice. The forum is quite a bit slower moving then here but there are some good members there with many years of experience of bikes, motorbikes and cars.

I'm all full of links for you here.


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## sunworksco (Sep 8, 2008)

This would be cool to build!
It has dual variable steering and Heinzmann motors.
Regards,
Giovanni


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## Woodsmith (Jun 5, 2008)

sunworksco said:


> This would be cool to build!
> It has dual variable steering and Heinzmann motors.
> Regards,
> Giovanni


It wouldn't be legal over here though.


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## Poohstyx (Dec 22, 2010)

A bit too chunky for my taste.
And while a dual steering system does offer some interesting possibilities (smaller turning circle, lane changing or self righting) they would all be too complex for my minimalist tastes.
The seat height looks about right for what I'd aim for 

The Challenge ligfietsen looks closest so far to what I'd aim for with the frame design.


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## Woodsmith (Jun 5, 2008)

Here's a couple of Jozzer's videos for you.










Jozzer is one of the resident electric motorbike builders here. He may be able to assist you in your plans as well. He is located in the UK.


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## Poohstyx (Dec 22, 2010)

Are 'off the shelf' controllers available that have the facility to switch between on-road and off-road use?
ie: a switchable 15mph speed limit.

Presumably I could then use any size motor, since the effective power would be limited to 200w for road use.


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## Woodsmith (Jun 5, 2008)

There probably isn't anything 'off the shelf' as such but Ebike throttles do often have a boost button.

Reading the rules carefuly the requirment seems to be a 'gradual reduction of assistance' as speed approaches 15mph. Not sure the best simple way to do that though someone good with electronics could sort it.

It may be worth looking at some of the Ebike kits that are available to see what controllers are used.

If you are doing a recumbent trike how about a legal rear wheel hub motor and two higher output front wheel hub motors for 'off road play'?


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## Poohstyx (Dec 22, 2010)

Been thinking some more.
with a 15mph speed limit, stability and wind resistance don't matter, so I may as well stick with a standard configuration trike. Still go for a low seat but put a motorcycle style front-end on with a rake of about 40-45 degrees.
If I keep the fork legs pretty short, I can then fit a low headstock and use a pair of apes to bring the bars up to my preferred height.

So how do the throttles work? do they just vary the voltage?


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## Woodsmith (Jun 5, 2008)

You mean something like this?








http://motorbicycling.com/f44/iride-customs-trike-7590.html

This one looks quite nice too.









This is one I made back in 1978 when I was 12. Not electric drive but would have been if the tech was available.









Even with the electric speed limit, personally, I would stick with the recumbent tadpole trike and a fairing so that I could pedal faster, and maybe sneak a little extra help in there once in a while.


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## Woodsmith (Jun 5, 2008)

Poohstyx said:


> So how do the throttles work? do they just vary the voltage?


Sort of.

The controller is a black box of electronics that 'chops' the DC into pulses. The pulses are then width modulated so that the square wave that comes out equates to a variable DC voltage as far as the motor is concerned. The throttle is simply a variable potentiometer that tells the electronics how the pulse is to be modulated.

Small pulse wide gap and the motor runs slower, wide pulse small gap and the motor runs faster. The pulses are usually around 5-15khz and so have to be protected from causing RF interferance.


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## Woodsmith (Jun 5, 2008)

Just found this:
http://visforvoltage.org/forum/6899-kmx-recumbent-tadpole-trikes-discounted-prices


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## Poohstyx (Dec 22, 2010)

From the first pic:
Put a seat with backrest (tractor seat possibly) about where the front of the rear wheels are.
Bring the headstock down to about level with the current seatpost mount.

So higher resistance = lower speed?
Then fitting a switchable resister will reduce max speed?


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## Woodsmith (Jun 5, 2008)

Poohstyx said:


> From the first pic:
> Put a seat with backrest (tractor seat possibly) about where the front of the rear wheels are.
> Bring the headstock down to about level with the current seatpost mount.


That'll look cool!


Poohstyx said:


> So higher resistance = lower speed?
> Then fitting a switchable resister will reduce max speed?


Not necessarily, it depends on the controller.
Some are 0-5k, most common are 5k-0 I think, some can be wired either way round.

I tried to add a switchable resistor in line with my tractor but it just messes with the controller. It checks to see if there is 5k when the throttle is off before allowing it to come online.

Maybe a physical limit stop on the throttle would do it but also maybe bike controllers have the facility built in anyway.
The ones I have played with limit the speed on full throttle but have a boost button that opens up a whole world of fun.


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## Poohstyx (Dec 22, 2010)

Presumably you can't power it up and let it do its self-test, then switch in the resister?

What advantages does the pulse system have over a simple variable voltage system?


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## Woodsmith (Jun 5, 2008)

Poohstyx said:


> What advantages does the pulse system have over a simple variable voltage system?


Well, Pulse width modulation (PWM) is an effective way of varying the DC voltage. Unlike with AC where you can use a transformer to change a voltage DC is difficult to change and so the motor is 'fooled' into thinking the voltage is lower by pulsing the high voltage so that the mean voltage going to the motor is lower. That then allows the motor to run slower and be speed controlled.

The other way to control a motor speed is to use a variable resistor so that some of the voltage is dropped across a resistance before it goes to the motor. The trouble with that is that power is also lost to the resistor as it gets hot and that is a waste of valuable battery capacity.


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