Fechter's current based throttle

[Mathurin]

OK, so a standard ebike accelerator ajusts to a speed, and the difference from this speed ajusts amps. So you could say it's a speed based throttle.

Well from the voltage forums I'd saved this pic. It shows a circuit that should allow the accelerator to be amp based. So, for example if you crack open the accelerator ro say 10 amps, then it's gonna try & hold 10amps for all it's got. So if you're rolling at part throttle pushing 5 amps you'll be going at a given speed. Hit a hill and it's going to slow down, stil burning 5 amps. Go down a hill and it's going to keep burning 5amps untill the speed is too high and the controller can no longer put out that many amps.

So it's more like a gas motor's accelerator, where you play on force to get your speed, rather then the other way around. The consequence is that it should be easier to go gentle on the batteries, especially if you've got lots of stop & go or hills.

Ok, so this thing has a pot to ajust the accelerator's zero, as I had done back when I had a throttle. But the part that's especially interesting to me is that it has a pot to ajust max amps. Since I've circumvented my controller's amp limiting capabilities, it's the batteries limiting the amps. So the idea is to use this circuit to limit my controller below 60amps, with a 60a fuse. This way I should be able to use better batteries without blowing the fuses all the time.

So before I dive into this, anyone see a reason why it wouldn't do the job at limiting amps? (I don't intend to put the bypass)

 

[knightmb]

I like the idea of adjusting the amps (I wish more controllers were like that). I'm wondering though, looking at the diagram, does that wire length for the shunt need to be exactly 12 inches? Seems that this circuit is setup to be very sensitive, I wonder what happen if the length is off. Don't know off the top of my head what the resistance of that length of 10 gauge wire would be.

I'm still don't understand exactly what this will do, could you give more examples?

 

[sabrewalt]

Interesting, It's basically an autothrottle but instead of being a speed control, it is an amp control, if it starts to draw more current, it just simulates you releasing the throttle a little bit. This is a lot like the trade off between airspeed and altitude in an airplane. Thats a stretch but that comes to mind. Be interesting if they invented that for cars... Set it to 45 mpg.. everybody would slow down on the hills LOL.

 

[Mathurin]

Oh, well as far as 12 inches AWG10 is concerned, I figured I could play with lenghts of AWG12 untill I find a sweet spot, or something... So long as it works.

And no, I really don't understand the circuit very much asides from the throttle zero ajust pot... The idea of that one is to add resistance to the ground, the effect is to raise the throttle's signal voltage. So, you ajust this untill just below the controller's "on" threshold, so that the throttle responds to just a crack of a turn, instead of having to turn it like 1/4 turn. Also the hall thing in the controller is not linear, it's painfully obvious on an analog volt meter. So opening the trottle sooner means it climbs up faster, and you can hopefully use more of the smoother part of the ramp and avoid part of the range where you get like a volt's difference for 1 mm of rotation... So it becomes easier to drive the bike at part throttle. For the rest of the circuit, I guess I'll have to scratch my head a bit more eh?

In my case, using this circuit as I belive it should work, say I open the throttle to 20 amps. Starts from 0 km/h and the circuit opens the throttle gradually more and more, always keeping 20a. Once it reaches 25km/h then it's running full throttle, so it can't keep up the 20a, but it keeps accelerating up to 32-ish anyways. And my hand on the trottle always stays in the same position, no need to gradually turn it as my bike accelerates.


And well cars pretty much allready have this, if you've set your accelerator for 100kph on the flat and hit a hill, your car will slow down.

 

[Mathurin]

I think all you have to do is twiddle that pot shown in the circuit instead of the wire. That is probably your fine tuning. Would be a useful circuit for maxamizing distance.

You must drive a pinto or something. Most autothrottles in cars push on the throttle, and hold speed, I think that cars that slow down just run out of usable power. Don't believe me, rent one with a fuel usage meter and watch the mpg's go DOWN(AMPS UP), when you hit a hill.

I don't know what an autothrottle is, I'll assume cruise control. That's not what this is all about. I was reffering to a plain, vanilla, accelerator pedal. If you keep it's position steady, the car will speed up going downhill, or slow down going uphill. That's what this adaptor is supposed to do, it works by plugging in between the throttle and controller.

The way the basic throttle that came with your kit works is that, if you turn it say 1/2 way, it'll bring the wheel up to a set speed. The difference between this speed and bike's speed determines the amount of amps beeing drawn, so starting from a stop with 1/2 throttle will suck amps, skid the tire and quickly reach a low top speed. In practice it's tricky to drive the bike for range with this because to avoid sucking/wasting amps you have to continuously ajust the throttle's position as you accelerate, go up/down inclines or just ease off the pedals.

Given Fechter's adaptor, if you turn the throttle 1/2 turn it'll make the controller pump out a set amount of juice regardless of the bike's speed. So, starting from a stop with 1/2 throttle would yeild a tamer start, but the bike would reach it's top speed. Or in the case of trying to go for long range, all you have to do is open the throttle a little, say so it gives you 250w of assistance. It won't spike up to 750 over the slightest hill, instead it'll slow down and keep giving 250w, unless the user gives it more gas. The end result making it easier to get more amps out of the batteries, and to get more done with the amps that get taken out of the batteries.

Obviously, with both systems, if you go full throttle that's what you're going to get.


Yes, Fechter's system has a pot to ajust the throttle's range over the controller's max amps. To use it I have to have a lenght of wire that's within the pot's ajustability range. I figure it'll take ~7 inches of AWG12 to equal ~12 inches of AWG10, with wire resistance data from here:

http://tinyurl.com/4wym5

I also see 12 guage was a poor choice given the amps to be shoved through it...

 

[sabrewalt]

Yep, That clears it up. BTW. The autothrottle term is used in airplanes. Same as cruise.

 

[safe]

I was over at the Voltage Forum before it got hacked and was following closely the whole idea about a "Current Based Throttle". It's an interesting idea that does make sense. In effect the throttle would only "restrict" amps in places that the normal controller would allow more amps (up to it's limit). The throttle is simply "restricting" the voltage to below what the rider imagines themselves as doing. Therefore if the user is holding half throttle at an rpm where the amps would be at the current limit normally you would instead get HALF the current limit of the controller. Or something to that effect.

I am on the "same wavelegth" or am I missing something?

Seems to me there are always three things:

Voltage
Current
RPM

The RPM you can adjust with gearing (multiple gears help a lot) and the Current is fixed to the internal dynamics of an electric motor and cannot be "forced" to be any higher than the physics allows. The Voltage becomes the only real area that one can modify to change the way the motor behaves in real world conditions.

My real question here is if anyone has done it yet?

Has this mountain been climbed?

 

[Mathurin]

Hi safe,

As far as I can recall it's hack value lies indeed in an ability to change the way the throttle works, and make it control amps instead. I'm mostly going on memory from the posts on V for the description of how it's supposed to work, btw.


I don't understand where you get the idea that the throttle is restricting the voltage to below what the rider imagines themselves as doing, though.

If I'm running at 10a on one bike with this module and one with a standard throttle, the accelerator signal to the controller and V & A should be similar in both cases... The only difference is the way the throttle is used, the standard throttle will have to be gradually opened more and more to keep the amps steady whereas with Fechter's hack I'd just need to open it to 10 and wait.


Noone that I know of has done it yet.

 

[safe]

It's taken me a long time to really understand the subtle points about how Current, Voltage and RPM's are related. The short answer is that you can't "force" the Current to be anything other than what it has to be based on the other two parameters Voltage and RPM's. There is a weird parabolic shape to the way power is created by the motor as the greater the load increases you also get a larger and larger efficiency loss, so the net effect is to cancel out all that extra power and get waste instead. In order to counter the wasteful situations the controller does this simple thing which is to limit the amount of Current that can flow to the motor. What the controller does is it forces the Voltage downward as the physical load increases thereby getting the same maximum Current but with less waste than an unrestricted motor. (and the same power... so it's like getting something for nothing)

So getting back to the "Current Based Throttle", the idea here is to no longer have a "flat" limit to the Current like the default controller gives, but to amplify the controllers restrictiveness by basically saying:

"How high should the Current Limit be?"

At full throttle the "Current Based Throttle" behaves exactly like a default controller and would limit the current to the default maximum limit.

At half throttle the "Current Based Throttle" would effectively reset the limit so that it would be lower in proportion to the partial throttle state. Half throttle would mean half the maximum Current limit.

The REASON one does this is to guarantee that no wasteful RPM/Voltage/Current situations can be reached. By excluding the possibility of some "bad settings" of the throttle you force efficiency out of the motor when otherwise you might be unaware of the mistakes you are making.

The "old way" was to stare at an Ampmeter and constantly try to get your throttle perfect... this simply "perfects" the throttle for you automatically.

And if you want to waste energy you can always open the throttle wide open and then it reverts to the normal wasteful scenarios of the default controller.

Last comment: When you choose a controller you often must choose 25 Amp, 30 Amp, 35 Amp, 40 Amp limits. What the "Current Based Throttle" allows you to do is to buy the highest limit as your controller and then let the circuit give you the performance of the lessor limited controllers depending on your throttle settings. The default controller setup will give you the maximum Current when you often don't want it or are unaware of it. Range is all about limiting the Current. Power is about maximum Current.

 

[Mathurin]

* Head desk *

 

[safe]

I'll be glad when the Voltage Forum is back in working order again. Hopefully some of the guys that posted there (like the one's into developing this "Current Based Throttle" circuit) will come around again. Frankly the electrical know-how that those guys have is beyond me and while I can read the circuit diagram and "almost" understand it there's no way I could develop my own circuits. (not now anyway)

 

[Mathurin]

Hey, don't sweat it man.

BTW, Fechter's registered on visforvoltage.org, but he's not brought up the current based throttle again, or not yet anyways.


I plan to try it as-seen above sometime within the next few weeks or so anyways, perhaps sooner. But first I have to fix up the controller again.

 

[safe]

I will be very curious how that turns out since you sound like the first person who will actually try the "Current Based Throttle" circuit.

It seems like the "Current Based Throttle" was just getting finalized when the hacker messed everything up. Hopefully we can get other lively discussions brewing in the future.

Why don't other people just come here?

I really don't remember how I got here, but I think someone had suggested to try this one out temporarily. It seems like this place would work fine for the kind of things that are needed of a messageboard. (is this some private companies site?)

Why bother repairing the old one when people could just pick up here?

(repost any ideas that seem important)

 

[Reid Welch]

Hi safe,

For me, this is the easiest of the forums to post in and to navigate.

I like the familar formatting and the ability to edit my old posts when errors beg to be fixed.

knightmb (Michael Brown) is the genial owner of this site,
and he's made it an alternative home for all of us.

I support this place and also I support the new Voltage forum.
I don't know if the old Voltage forum will come to life again. Seems unlikely...

Glad to read your work here. Smart stuff.

Thanks, and best to you,

Reid

 

[safe]

Thanks Reid, I was a late arrival to the Voltage Forum and was just getting warmed up when it was hit. I like being able to post pictures easily because so many things are easier to express with them. I'm not a fan of the Voltage-dot-net site, I don't like the formatting and there is not that much activity going on there anyway. I have no idea what happened to some of the "regulars" of the old forum and wonder if they simply lost interest.

This site is very nicely built and if (for the time being) people just came here it would work well. I haven't signed up over at Voltage-dot-net site, but if you have maybe you could post a message there to have people come here?

 

[fechter]

Gee, I guess they'll let anybody join this board. Sorry I didn't get over here earlier.

It sounds like Mathurin has a good understanding of how it's supposed to work. Throttle position controls the current limit from zero to whatever max you want. This should work wonders for increasing range with SLA batteries.

Anyway, as far as I know, this circuit has not been built or tested yet. It's on my to do list... somewhere. Mr. Electric has all the parts and was going to try making one too.
Since it hasn't been tested, there's a good chance some tweaking may be necessary, but I think the schematic should be pretty close.

One variable that's hard to predict is the shunt resistance. I showed a 1ft. piece of 10ga., but that's really a swag for a minumum resistance. I had intended the circuit to use existing wiring, so no addidtional resistance would need to be introduced. A higher or lower resistance would change the resistor values, but since they're adjustable, it should be able to compensate.

 

[safe]

fechter !

The "electrical royalty" has returned !

What about the possibility of switching to the Hall Effects version instead of the shunt? It might cost $5 more, but since you could identify the appropriate component more easily than getting a wire the EXACT length right you would be making a circuit more universally adaptable.

The idea is great... by varying the throttle setting you are more or less reprogramming the current limit of the controller. That allows a higher current limit to be used to start with and yet you can still get the "economy mode" when you use less throttle.

I WANT ONE !

Note: You might also think for second about how you could make a small little business out of this product if it works as expected. If you design a completely "bulletproof" circuit that simply uses the standard 5 Volt throttles in widespread use then that universality might mean that hundreds of people would want one too. Build it for $10, sell it for $50. With the Alltrax Controllers costing $300+ it's a quick way to get a controller improvement for a small amount of cash. (and the Alltrax is more suited to the needs of bigger bikes, not the small ones) If it's a "hit" you might even get into the mainstream electric scooter market and it becomes a standard modification that every kid with an electric pocket bike will want to have. Geez, kids will by stuff just because it looks cool and when it actually improves their machines performance they (or their parents) will easily pay the price.

 

[fechter]

Using a hall current sensor would eliminate some of the guesswork for the resistor values. For my setup, I would need a 100 amp one. The hall sensor has several other advantages, like temperature stability and high sensitivity.
The "existing wire" shunt setup was used mainly because I'm cheap, and doesn't have any maximum current limitation.
If I can make it work with a shunt wire, it should work better with a hall sensor.

 

[safe]

These are some graphs that demonstrate how the "Current Based Throttle" SHOULD modify the behavior of your motor. The three graphs are for 1/3, 2/3 and Full throttle settings and would represent the amount of Power output in Watts as you go from zero on the left to maximum rpms on the right.

Note: This is for a 1200 Watt motor with a peak current limit of 75 Amps, your results would be different with other motor combinations.

Some additional thoughts on this "Current Based Throttle" idea.

Normally when you use less than full throttle what that does is it contributes to the lowering of the voltage. For any given voltage there is a corresponding amount of current that matches that voltage for a specific motor. The controller "controls" the situation by sensing the current and preventing it from going any higher than the maximum current limit that it was programmed to have by forcing the voltage downwards, but only enough to satisfy the limit of the controller.

So the rider might not know exactly what is going on when they are using less than full throttle. Depending on the load conditions that partial throttle setting might STILL be producing the maximum current OR it might not, you just DON'T KNOW.

If the "Current Based Throttle" can sense that the current being used is above the "partial-ness" of the throttle (in other words 1/3 throttle needs to translate into 1/3 current load allowed) then you can guarantee that if you are trying to preserve energy that you are in fact doing so and not just kidding yourself.

The ultimate effect of this idea would be to allow for a "perfect" efficiency motor at (say) 1/3 throttle and still have the ability to dump heavy current loads when you run into some monster hill that you could not get over if you were always in "efficiency mode".

It's a great idea... I can't wait until someone does it... ( people with undersized motors should be especially interested because it really effects the small motors much more than the large ones which usually wouldn't need it)

 

[fechter]

At a given setting, the current mode throttle will maintain a constant input power to the motor until the load drops off.

If I give it 1/4 throttle for example, it would accelerate to full speed (and full motor voltage) if the full speed load is under that current limit. Like going downhill, you could get full speed with a very small throttle setting. Going uphill or into the wind, you would need to increase the throttle setting to make full speed.

I have all the parts here to make one. Just need a bit of free time.

 

[safe]

Correct me in every way since I'm probably about to make errors in electrical circuitry theory, but here goes:

Here's what I don't understand...

The "Current Based Throttle" SHOULD be able to sense the amount of current that is going towards the motor. From this knowledge the circuit can then reset the throttle position so as to direct the controller to lower the voltage if the current sensed is too high.

I think I got that...

But how do you deal with the "starting maximum current setting" issue?

Let me throw out some numbers:

Controller Limit 40 Amps - Full Throttle then allows 40 Amps
Controller Limit 40 Amps - Half Throttle then allows 20 Amps
Controller Limit 40 Amps - Quarter Throttle then allows 10 Amps

And also:

Controller Limit 100 Amps - Full Throttle then allows 100 Amps
Controller Limit 100 Amps - Half Throttle then allows 50 Amps
Controller Limit 100 Amps - Quarter Throttle then allows 25 Amps

So how does the circuit know what the initial setting should be?

How much flexibility can you make into the design so that it would work with just about ANY controller?

 

[safe]

BOOST CONTROL

And as a completely separate question:

What about a circuit that simply "sets" the current limit externally?

Rather than integrating the current limiting functionality into the throttle itself what about a separate knob that might be called your "boost control" which you can either turn UP for maximum power or DOWN for maximum range.

This idea allows someone to not be so "prissy" with the throttle. You could still crack the throttle wide open all the time when the setting is set low and be certain that you would get the best range possible.

Something to think about... :wink:

(the idea of a separate "boost control" is even more attractive than the integrated throttle option to me)

 

[Mathurin]

"The "Current Based Throttle" SHOULD be able to sense the amount of current that is going towards the motor. From this knowledge the circuit can then reset the throttle position so as to direct the controller to lower the voltage if the current sensed is too high."

The circuit senses current going to the controller, not to the motor.
It generates a throttle signal in function of amps & the throttle's setting.



"So how does the circuit know what the initial setting should be?"

This circuit has a pot to ajust max amps.


"What about a circuit that simply "sets" the current limit externally? Rather than integrating the current limiting functionality into the throttle itself what about a separate knob that might be called your "boost control" which you can either turn UP for maximum power or DOWN for maximum range. "

This circuit has a pot to ajust max amps.
Mount it on your handlebars and add a "boost control" sticker.

 

[D-Man]

cancel

 

[safe]

"What about a circuit that simply "sets" the current limit externally? Rather than integrating the current limiting functionality into the throttle itself what about a separate knob that might be called your "boost control" which you can either turn UP for maximum power or DOWN for maximum range. "

This circuit has a pot to ajust max amps.

Mount it on your handlebars and add a "boost control" sticker.

So in effect the "Current Based Throttle" would be a kind of "Boost Control" in your opinion?

Here's the thing:

What happens in those nasty situations when you are using partial throttle (having no idea how much partial throttle, the other thread was talking about how imprecise they can be) and you desire a low current limit, but because you are on a moderate hill the load jumps through the roof anyway? (and you might not even know it)

In a pure "Boost Control" setup the current limit is directly related to the adjustment of the "Boost Knob" (pot). You can NEVER exceed the current limit no matter what conditions occur. Ever!

With the "Current Based Throttle" you would normally set the maxmum current of your circuit to equal the maximum current of your controller. (otherwise what's the point of having it?) The "Current Based Throttle" would then establish the current limit allowed through of the controller based on the open or closed status of the throttle itself.

Don't forget also that there are some situations where having TOO LITTLE current actually REDUCES efficiency. There are both sides of the curve to deal with and if the throttle is varying the current limit as it goes and the "Boost Control" is already turned down you just have one thing "fighting" the other and the result can be a too low current situation.

There's such a thing as "Keep It Simple Stupid" in design.

The "Boost Control" is a simpler design than the integrated throttle setup as I understand it. With "Boost Control" you can be assured that the desired current is being used. With the variable nature of the current based throttle (1/2 throttle means 1/2 Boost setting, which can mean just about anything) you open a "can of worms" of problems.

The "Current Based Throttle" is a great idea, but it requires a very sensitive touch on the throttle to use it. The "Boost Control" allows you to think about other things than the throttle. (like watching the scenery)


SET IT AND FORGET IT - The Boost Control Advantage?