How to get the best out of the e bike?

[mike_j]

I am exploring the characteristics of my new 8fun bike in an attempt to find how the power is controlled (control algorithm).

The motor has no output above about 15mph - presumably this is measured by motor speed with the wheel diameter being a known constant.
The level of assist is set by the selector at three levels.
The pedelec knows how fast the crank is tuning.
I'm all OK so far.

BUT:
the system doesn't know how hard I am working (crank torque), what gear I am in or how fast I want to go - so how is output set?

Is output ramped up if I change up or down a gear?

How do I make it increase output so I do less work for a given speed and assist level - pedal faster in a lower gear or slower in a higher gear?

Generally - how do I get the best out of the system in terms of speed, gear and manual effort?

Purely a side issue but for interest what does a typical electric bike weigh? Mine weighs in at 19.8kg unloaded and a disgraceful amount more with me on it.

 

[Scottyf]

I think generally it depends on how sophisticated the controller is for each setup.
Some Of the older contolleds litters my used the pedelec function as an off switch to apply motor power. The assist level or 3 speed switch was a basic 80%, 100% or 120% throttle adjuster.

More advanced systems controller use a series of ramps to find out user input from the rpm your legs are spinning while using the back emf from the motor to determine speed.

That's as much as my basic info goes really

 

[andyh2]

I've just been trying mine out. It's a 20" wheel and assist seems to end at 13mph, but the hill climbing seems pretty good.

Ian posted regarding his kit that the pedelec sensor seemed to give max power once 40 RPM is reached. I'd assume that you can increase cadence as much over that as you like, and continue to get max power.

As far as I can feel the 3 levels are not so much power levels as motor speed levels. Level 1 assists up to about 7.5mph, Level 2 10mph and Level 3 13mph. For hill climbing it seems happier in Level 1 or 2 as in Level 3 it's trying to go faster than it's got the power to deliver on. Well I suppose that should be it's trying to go faster than I've got the power to input

So whilst it's no speed demon it does make hill climbing very easy going, provided the speed is kept above 5mph.

It's nice having the choice of throttle or pedelec. The throttle being good for fine control in town and the pedelec nice on the open road.

I don't think this set up would be that good in a flat area as, unless there's a head wind, 13+mph would be easy to maintain without a motor. It's quite hilly round here so I'm expecting it to be quicker uphill and on the downhills the extra weight won't be a problem.

 

[NRG]

I am exploring the characteristics of my new 8fun bike in an attempt to find how the power is controlled (control algorithm).

The motor has no output above about 15mph - presumably this is measured by motor speed with the wheel diameter being a known constant.
The level of assist is set by the selector at three levels.
The pedelec knows how fast the crank is tuning.
I'm all OK so far.

Only very few systems measure wheel speed and ultimately speed is limited by motor design. Motors like the Bafang come in a number of speeds IE: they are wound for a particular speed (15mph say) for a certain wheel size (26") driven by a certain voltage (36v)

So a 200rpm 36v motor in a 26" wheel will give an unloaded speed of 15.5mph. This speed is a design choice and is limited by the motor back EMF equalling the supplied battery voltage.

The typical 3 way handle bar switch fitted to most bikes and kits simply sets a scaling factor for the throttle. IE: level 3 assist maybe programmed in the controller to give 100% throttle or in other words full rotation of the throttle gives full battery voltage to the motor.

Lets say level 1 assist is programmed to 50%, this means full rotation of the throttle only gives 50% of the battery voltage to the motor IE: 18v

As BLDC motors are voltage controlled devices 50% voltage means 50% RPM or half speed. E-Bike throttles do not control power directly only voltage, some get confused by this as by switching the assist level while riding can see the bike accelerate, however, if the load on the motor is high enough (climbing a hill) switching to a higher assist level does nothing...

BUT:
the system doesn't know how hard I am working (crank torque), what gear I am in or how fast I want to go - so how is output set?

Power output is a function of Torque and RPM. As RPM lowers the torque rises, with torque being maximum at 0 rpm. Tillson made a very good post about the relationship of Power, RPM and Torque here:

http://www.pedelecs.co.uk/forum/electric-bicycles/8860-torque.html#post108423

Is output ramped up if I change up or down a gear?

Unless your bike os fitted with a torque sensor the controller has no idea of how much effort the rider is inputing. Systems like the Panasonic one measure rider input and there are some hub bike systems like the Raleigh bikes that also measure input.

How do I make it increase output so I do less work for a given speed and assist level - pedal faster in a lower gear or slower in a higher gear?

You cant as it stands, its a fixed power output system. Theres no feedback to the controller on speed or rider input. You would need to fit something like a Cycle Analyst that has the ability to control battery current delivery to have any degree of control over power.

Generally - how do I get the best out of the system in terms of speed, gear and manual effort?

What do you mean by 'best'. Best speed is inbuilt to the system, to go faster you need to either change gearing and rider harder or change motor / voltage to get more speed from the system. Best range is achieved by either riding above the assist limit or limiting battery draw by lowering the current limit....

Purely a side issue but for interest what does a typical electric bike weigh? Mine weighs in at 19.8kg unloaded and a disgraceful amount more with me on it.

Under 20Kg is good, the lighter the better. Typical hub powered bikes weigh in around 25Kg...this becomes an issue if you wish to maximise range by using more rider input than motor...a heavy bike is not nice to rider without power!