19 replies to this topic

[paulrockliffe]

Not an automatic choke, I've read a load of threads about those and I definitely want to stay in control of the choke position.

 

What I want to do is add a stepper (?) motor to the choke and use a potentiometer (?) to let me put a nice switch on the side of my control box to let me dial the choke on and off without pulling on a cable and having to twist it to lock it in position.

 

I've added a longer cable so I can move the choke as I can't reach the dash from my seat, but it's still not really long enough so I'm wondering if a wired solution might be neater and easier to use.

 

Does anyone have any idea what the basic kit I'd need is?  I've not done anything along these lines in along time, so not really sure where to start looking.

 

And more out of curiosity than anything else; what are the parameters the dictate the need for the choke?  Is it purely engine temperature?  ie if I took the engine temperature gauge wire and fed it into an Arduino would it be possible to map an automatic control for the choke based on the engine?  Or would you need more data than that to be able to do something reliable.

 

Cheers

[paulrockliffe]

Having a quick look I think it will be easier to use an arduino, so my question is really how do I know if a stepper motor is strong enough to rotate the choke or would you remove the spring form the choke?

 

Ta.

[Ethel]

There was a factory carb with a stepper motor, Montegos and similar age wagons had 'em. I wouldn't think it would be too difficult to cobble together some code for an Arduino. Adds some bulk though some might not fit as a direct swap

 

I've got mine on a radio control model servo, I think others have done that too, tmf topic somewhere?

 

Stepper motors are strong,  it would make sense to remove the spring but you'd nee a solid connection that can push as well as pull. My servo setup seems to work ok with the spring in place.

[paulrockliffe]

Thanks, I've found some easy Arduino projects that list all the kit and give you the code, so I'm confident I can get that working and programmed for the maximum and minimum angles required.  It'll just need a bracket making to put the motor on the shaft, which shouldn't be too difficult. 

 

The Arduino will go behind the dash easily enough and I was planning to put one in anyway to build a custom LCD dash eventually so I might as well start with this project and build from there.

[Ethel]

Looking at this reminds me you'll need to incorporate a fast idle somewhere

[paulrockliffe]

I'm not sure I understand, is that different to the choke itself? 

 

I was planning to simply replace the cable turning the spindle that has the cam thing on that pushes on the nut.  Stepper motor on the end of the spindle, remove the spring and  let it do exactly what the cable was doing.

[Ethel]

Sounds good, from the exploded diagram you can see SU chose to dump the original linkage and reinvent the wheel instead.

 

I mounted my servo above the manifold flange and made a pushrod out of a knitting needle  . I'd grab some photos but the car's buried under a pile of floor insulation at the mo.

[Dusky]

Could always buy a long choke cable and mount it on the floor behind the handbrake, like on the old fiat 500's.

[paulrockliffe]

I bought a long cable to mount between the seats, I was putting a control box there.  But for various reasons the control box is going to the right of the drivers seat now, and the choke cable isn't long enough to reach across the seat as well.  I'll lash something up between the seats temporarily, but the reality is that any cable is a little tricky to use unless it's fairly straight and in front of you. 

 

It would probably go best on the steering column, but I've order the electronics now.......

[carbon]

Paul,

 

I have a NOS HIF44E somewhere in the garage if you go down this path...

[paulrockliffe]

Hello, what just seen your post. I'm going to Diy it with the Arduino.

I've bought the kit, but I just waiting for the stepper motor to arrive. It's surprisingly straightforward so far, I have a knob that controls the speed an LED, so just need to swap the LED for the motor and work out a scale factor so I get the right angle of rotation.

The hardest bit is going to be the bracket I think.

[Ethel]

Is it the map function on Arduino that does the scale factor for you?

[paulrockliffe]

No idea, I was just going to multiply or divide the output to the stepper by a factor so that 270 degrees at the dial = 40 degrees at the motor, or whatever the right number is.

But I've not looked at this bit at all, no point until the motor arrives.

[paulrockliffe]

Got my motor today, wired it up and tested it then set about trying to code it for what I want.

Ethel, having looked at it, yes the map function will restrict the range of movement, but I think you can do it a few ways.

Problem I've had is that the potentiometer is returning a value between 0 and 1000 and this needs to translate to 1 of a number of steps between 1 position and another, which is choke off to choke fully on. The stepper doesn't know where it is so you can only code it this way by telling it to move further in one direction or the other.

Most of the code examples compare the potentiometer values with the last value, and if it's higher move the potentiometer. Problem with that is that it needs the stepper to move faster than you can move the potentiometer and I'm not sure how each loop through the code interacts with the last.

I know it's all wired up right, but the code I've tried doesn't move the stepper with the potentiometer. It seems to do something but it's as if it's recalculating before the stepper has moved.

Anyway, I found a method using a rotary encoder instead that looks better, so I've ordered one of those.

[paulrockliffe]

I had a think about this on the way into work I *think* what's probably going on is that the potentimeter value fluctuates up and down due to noise on the voltage signal or the quality of the components, so the motor is following the fluctuations rather than the rotation of the knob.  

 

I'll change the rule so that the value has to change by more than 5 or 10 before the stepper moves and see if that irons out the fluctuations and fixes it.  

 

But I think the rotary encoder will be better because the plan is to work out a map between choke angle and engine temperature and automate the choke, in that scenario the encoder will work as an off-set from the map to allow you to dial in the map perfectly as I doubt there'll be a perfect correlation between temp and choke required. 

 

I think I'll start by getting it to work, then program full choke when the engine is cold.  The encoder also has a push-to reset button, which I can use to reset the choke to on if cold or off if warm.

 

I ordered a few other bits and pieces including an LCD display so I can monitor the outputs as I go as it'll help wit the guesswork! 

 

I would have loved a ton of this stuff when I was a kid!