Throttle and Current Limit Theory

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Final Thoughts

Fechters "Current Based Throttle" will really open a whole new world of possibilities for people that use any type of fixed gear with their motors. By "squashing" the powerband of a normal motor you can "lean" out the power and get speed with a far lower "cost" in terms of energy usage without sacrificing anything at full throttle. (you still have low end torque if you want it)

The "combined" solution should not be overlooked however because it comes in as a "compromise solution" that splits the difference between the two extremes. In practice the "combined" solution might seem a little less "weird" to ride.

Anyone who is really "into" electric bikes should be thinking:

"FECHTER, WE WANT A CURRENT BASED THROTTLE OF OUR OWN!"

 

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A "post final" thought.

Take another look at the "peak power" values for the "combined" throttle solution. Notice how the range is CONSTANT.

CONSTANT RANGE?

Yeah, one of the weird things about the way the "combined" solution works is that you are basically always operating at a constant "burn rate" of energy if you are "in the powerband". So a big argument for this would be that it increases predictability of behavior of the bike. You can know that if you use the throttle in a manner consistent with the speeds you are going at (not cracking open full throttle all the time) that the bike will always travel the same distance. This might be helpful in making sure you don't run out of battery power unexpectantly.

 

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Fun With Charts

These are kind of interesting...

The first chart is top speed attained for each of the various throttle control options.

The second is range.

(rpm is the x-axis)

 

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Range

I hope people have realized the philosphical significance of the final results here. (sometimes people get lost in the details and miss the "big picture")

The "grand realization" about the "Current Based Throttle" is that you can effectively "lean" out the motor (sort of like running a gasoline motor very lean) and stretch out your range. This chart shows the enormous potential of the "Current Based Throttle" in the ability to extend the range. The "Combined" throttle is also very good, but it's actually a compromise solution.

Try to "get your head around" this chart. It demonstrates how the three different throttle systems behave in achieving range. (take a little while to figure it out)

This should be having people go "WOW". (but I don't think people are quite comprehending it yet) Fechter "understands" because he had the wisdom to suggest the idea in the first place. I "get it" now, but didn't in the beginning.

 

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Further Analysis

The parameters that define range are:

1. Energy being used.

2. Rpm at which the Energy is being analyzed.

3. Wind Resistance that occurs at the rpm used.

The thing that pops out about the "Current Based Throttle" is that is allows the rpms to remain high. That's VERY important. Both the "standard" and "combined" throttles reduce their duty cycles (and thus reduce their peak voltage) and that means that the rpms become limited by the throttle. While it's possible to get reasonably low power usage at partial throttle with the "standard" system you can't go very fast, so the overall range is not that good. Only the "Current Based Throttle" allows the voltage to remain high, but simply REDUCES the load that it can carry. The "upper bound" of load on the flat land is based on wind resistance.

So I reverse my decision about which type is "best", at this point I'm going to say that the "Current Based Throttle" is the best of the three options possible. Though I do think that the "combined" gets second place and the "standard" comes in last.

I see no benefits to the "standard" throttle at all.

Can ANYONE point out ANY reason to use the "standard" throttle other than the fact that this is how it's normally done?

 

[Toorbough ULL-Zeveigh]

Simple City
ERGO
Monet

 

[Matt Gruber]

Which type have you implemented?

Are you doing "current limiting"?

Or are you doing the "combined" concept of BOTH "current limiting" and "duty cycle limiting" (so it's linear) at the same time?

There are many "flavors" of limiting systems after all...

(there's also simple static throttle limiting like "Boost Control" which is a whole other category)
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ANSWER
on a hill it cuts input amps.
level it cuts output volts.
in variable winds it maintains a surprisingly steady speed.