Taming the twist grip throttle

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Geoff V

100 mW
Joined
Jul 30, 2012
Messages
39
Gentlemen

Before anyone starts whinging about not searching this Forum, I've spent hours looking for an answer, without success so far, now that's out of the way here's the question.

My understanding is that the typical ebike controllers are simply speed controllers, which is fine if you have just 250w available, but become unpleasent/dangerous to use with higher power installations especially mid drive units in a low gear. Starting off and low speed control are almost impossible to achieve smoothly, without at best surging and at worst finishing up on one's backside. I'm fairly clear that the correct way to cure this problem is by using a more appropriate controller with current control but for most non tech riders like myself this is not a realistic option, yet.

Whilst discussing this problem with a friend with a view to creating an exponential voltage change from the twist grip rather than a linear change, he suggested an electrolytic capacitor between the negative lead and the output lead from the twist grip might soften the voltage change enough to make the bike rideable.

Does any one on the Forum have an opinion on this as a 'temporary fix' and if viable, what value of capacitor would be required with an Infineon controller.

I'm astonished this problem has not been solved, or has it?

My thanks in anticipation.

GeoffV
 
i would sure like a solution as well! even having mastered the speed based throtle,,,,,,,

I think the v3 beta cycle analyst has a well implemented current based throttle. Perhaps phase current could be monitored with a shunt and this would produce real torque control with an infineon/ecrazyman, which has a poor throttle for higher voltage/power. imo


mabye someone with real experiance can pipe up :mrgreen:

another issue is whether the throttle is even giving out the proper signal (linear) to begin with.which hall throttles probably dont. Which might be fixable with methods throttle pots.

IT WILL EVENTUALLY BE SOLVED
 
The problem, as such, is that it's difficult to solve. Ebike controllers generally are all speed controllers, where the throttle sets a speed demand for the controller, pretty much more or less a motor applied voltage control. One reason they work like this is that it's easy to do.

Ideally I've always thought we wanted a torque control (a bit like the throttle on a car or motorcycle), but that requires the controller to measure the motor phase current (which means at least two current sensors on the phase leads). A workable alternative is to use power control, where the throttle controls the battery current. There is a way to do this using an add-on, like the CA. I've not tried it, so don't know how it feels.

One thing I can say for sure is that slugging the throttle voltage response down with a capacitor is a very bad idea. What tends to happen with a slow throttle ramp is that you open the throttle, nothing happens (because of the delay) so you open it a bit more, then the voltage starts to rise fairly quickly and you need to close the throttle, as now things are happening too quickly. The problem now is that the capacitor holds the throttle voltage up, so closing the throttle is equally sluggish.

There are ways to fine tune throttle ramps, and make them unidirectional (so they slug the open throttle response but act instantly to the closed throttle demand), but it still feels pretty horrible.

One way that does work tolerably well is to alter the linearity of the throttle, so that a small throttle movement from closed gives a very small voltage change at the controller, and a larger throttle movement makes an even larger throttle voltage change. This allows more sensitive control at low throttle settings, yet still gives a reasonably good overall response. The easiest way to change the throttle linearity is probably to use a small ucontroller between the throttle and the controller to intercept the signal and apply the appropriate function before outputting the amended voltage. I think someone here has done this, but I'm not sure how well it worked.

Another way to get a similar effect is to fit the three speed switch to the handlebars. All the Xiechang controllers allow the switch max speeds to be programmed, so you can start off with the switch in a low position, giving a much less sensitive throttle, then switch to a faster speed when you want to go faster and can accept the coarser throttle control.
 
I am finally happy with the current throttle response of my project, I tried many ways to get this nailed I first done the 3 position switch ( as JH has described ) it was a very easy way to tame the initial problem and in general I would say the easiest/cheapest way to solve the problem, but it was not good enough for my needs then I tried a log throttle response ( also as JH has described ) although this work reasonably well it was quite difficult to get it to work well for my needs and a bit more trouble than it was worth, I now have a setup that I am more than happy with and this is battery current limiting, the CA does this but I have done my own version ( dont involve a CA ) and it was based on a original circuit posted be fetcher ( forum member ) details can be found in this thread towards the end of this thread http://endless-sphere.com/forums/viewtopic.php?f=2&t=33963&start=30
 
Gentlemen

Thank you for going to the trouble of replying to my question.

Jeremy
You have confirmed my concerns about the capacitor idea, an exponential voltage ramp seemed to me a better route to try, but I value a second opinion.
I have tried controlling the battery current with a CA version 2.25, but to get over the problem requires reducing the Battery current limit to the point where one might just have well bought a 250w installation.
There is a thread which I spent much of yesterday reading which concerned a non linear interface between the twist grip and the controller, unfortunately a girl friend appeared on the scene and the thread died!

Hydro-one
Thanks for your contribution, as you say "one day".

Gwhy
Thank you also, I had noticed the three switch option but it doesn't appeal, seems to me to be more expenditiure for a less than satisfactory 'fix'.

GeoffV
 
Controlling the battery current is a 100% fix. The trick is to ramp the current limit as a mix with the speed based throttle. What causes the problem is that as soon as a speed based throttle is opened the controller will want to put max current limit into the motor so this current limit also needs to be linked to the throttle. The CA achieves this but I think it can be quite difficult to set it up to get satisfactory results. It sounds like that you tried the wrong thing with your CA and just set a low overall current limit.
 
Gwhy

You bring good news, but unfortunately more questions as well.

I mentioned earlier that I have a CA version 2.25 and have read the manual fairly carefully without spotting the facility to program it as you suggest, can you or any other readers of this thread throw any more light on the subject, as you correctly summise, I have simply tried setting a battery current limit.

I wait in hope and anticipation.

GeoffV

p.s. I think the CA is a wonderful piece of kit, thank you Justin.
 
Quick thumb on the three speed switch might be as good as it gets for now.

The switch works great if your needs are to ride slow for awhile, then you can switch to high speed once out of a congested area.

If you are using a full grip twist throttle, I found it easier to micro controll a half twist myself.
 
Geoff V said:
Gwhy

You bring good news, but unfortunately more questions as well.

I mentioned earlier that I have a CA version 2.25 and have read the manual fairly carefully without spotting the facility to program it as you suggest, can you or any other readers of this thread throw any more light on the subject, as you correctly summise, I have simply tried setting a battery current limit.

I wait in hope and anticipation.

GeoffV

p.s. I think the CA is a wonderful piece of kit, thank you Justin.
Click to expand...

I have no practical experience with CA's ( I dont own one ) But I do know that this has now been implemented on the newer CA versions, Hopefully someone else will chip in with more detailed info for you as regards the CA that you have.
 
Gentlemen

Thanks once again for your contributions.

I have incorporated an 18 turn 1k pot in the negative lead to the hall sensor, as suggested by Fechter, which has permitted me to remove almost all the dead space at the start of the throttle rotation. I also took advice from Dogman, thanks, and split the twist grip so most is fixed and only the inner part of the grip rotates. These mods are far from being perfect but at least the motor control is now tolerable until either a proper controller becomes available or I splash out on a CA v3.

Safe cycling to you all.

GeoffV
 
Morning Guys,


I've been working on a solution to this problem this last week,. Winter time I develop R&D for ebikes and summer time I Ride! :D

I have made a little harness that attaches between the throttle and controller that will allow you to apply different curves to the throttle response. I also added a button on there that allows you to toggle modes and even a cruise control if anyone dares. I don't do cruise, I like to have control at all times with the speeds I like to go :D Lol

How it works.. You connect one side to a controller. From the controller you get power to power up an Atmega328 that also powers up a DAC and ADC .. Then you connect your throttle to the other side.

What the code does.. It looks at the ADC which reads the input from the throttle (The controller power goes to the throttle) I then apply some math functions for EXPO like RC controllers to the throttle and output the value to a DAC. Using A button the user can select between different modes and by holding the button on a fixed throttle position the user can cruise.

I tested it out on the weekend and it's working great. I will post up a youtube video of it live and in action when I get a chance this week.


Mo
 
Yeah it's actually working surprisingly well. I thought there was someone on here working on it a year or so ago but I didn't see it develop. I recently learned a decent bit of hardware and software at work which made me feel comfortable enough to try it.

I apply 2nd and 3rd order polynomial curve fits to the ADC input curve and do piece wise calculations on 3 segments of the throttle range. I'm using a 12 BIT DAC and 12 BIT ADC. I'm getting pretty good throttle resolutions. I put a screen on the one I'm prototyping and could easily add the ability to make custom curves that are displayed on graphical screen but lets just see how this pans out first.

I'm working on something else now too. I got some digital potentiometers that I plan to interface to mean well style power supplys .. Add a screen 3 buttons and BAM you have a fully controllable charger that allows you to change Voltage and Current using 3 buttons and a little LCD screen to see whats going on.

I'll try and do that one next week.. Work sucks.. Little time for play :(

Mo
 
back about a bazillion years ago there was a thread titled "Fechter's Current Based Throttle". It started out discussing an addition and mods to the old Crystalyte 12FET analog controller. but by the end there was a stand alone circuit that could be added to anything. the thread is about 15 pages long and the schematics and pcboard layout are about page 10.

Based on Fe chter's design there was a spin off using an ACS750 current sensor IC. to do "Armature Current Limiting". started by Fechter it was hijacked by a now banned member "Safe". but it still explains the idea well.

these were analog designs using single op amps and a couple of trimmer resistors. no programing skills required. if you are interest just search for the thread titles.

rick
 
Geoff V said:
I mentioned earlier that I have a CA version 2.25 and have read the manual fairly carefully without spotting the facility to program it as you suggest, can you or any other readers of this thread throw any more light on the subject, as you correctly summise, I have simply tried setting a battery current limit.
Click to expand...
Geoff V said:
...or I splash out on a CA v3.
Click to expand...
You have employed the current limiting feature which is exactly what it says - it puts a ceiling on the battery current but has nothing to do with the throttle curve. Up until you hit the ceiling, the limiting is not in effect and the throttle behaves as if the CA is not connected at all. When the limit is exceeded, additional throttle has no effect, effectively producing a throttle dead zone at the top of the rotation.

However, the V2 CA does support a 'current throttle' where the throttle rotation is mapped to the configured max current limit. This is described in section 9.3 of the v2.23 CA Manual. In this mode 25% rotation yields 25% max battery current, etc. This goes a long way towards getting the throttle under control.

Since you have a CA V2 in hand, I recommend you have a go at the 'current throttle' setup. This may not cure all your difficulties but I am certain things will be improved.
 
I haven't tried this yet, but it may or may not give better throttle control.

http://www.cyclegear.com/eng/product/Motorcycle_Throttle_Control/web1001431
 
While this is for a volume control, as opposed to throttle control, this circuit may work on a normal linear throttle:

http://sound.westhost.com/project01.htm
 
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