Nosewheel Steering Tiller for Zibo

[Keith Baxter]

A stepper motor cannot be used as an input, because it gives no feedback. A stepper with feedback, always relies on something like an encoder or a potentiometer, but those would be the regular inputs we have.

Hi,

I thought that there is some reading coming out of the stepper motor. Like on my 3D printer and CNC when the power is off and I move one of the axis manually, the stepper motor is rotated and light pulses.

How is that working. Do you know? I would have thought that it is generating pulses.


Keith

[jph]

Hi,

I thought that there is some reading coming out of the stepper motor. Like on my 3D printer and CNC when the power is off and I move one of the axis manually, the stepper motor is rotated and light pulses.

How is that working. Do you know? I would have thought that it is generating pulses.


Keith

Hi Keith,
You are seeing a small back EMF pulse from the stepper. That is all.

[Keith Baxter]

Hi,

I thought that there is some reading coming out of the stepper motor. Like on my 3D printer and CNC when the power is off and I move one of the axis manually, the stepper motor is rotated and light pulses.

How is that working. Do you know? I would have thought that it is generating pulses.


Keith

Hi Keith,
You are seeing a small back EMF pulse from the stepper. That is all.

Joe,

Is it not possible to read that EMF pulse? If we can read it then we can use it. What pins on the motor will that EMF pulse come from? Or can it be read from the ULN2003 driver card?

Keith

[jph]

A stepper motor cannot be used as an input, because it gives no feedback. A stepper with feedback, always relies on something like an encoder or a potentiometer, but those would be the regular inputs we have.

100% - a stepper is a pure output device.

If someone really wanted to create a two way positional system then It is virtually identical to the issue of the 'trim wheel' with both manual and auto (motorised) positioning which has been discussed several times.

Joe,

Is it not possible to read that EMF pulse? If we can read it then we can use it. What pins on the motor will that EMF pulse come from? Or can it be read from the ULN2003 driver card?

Keith

Unfortunately not in any reliable way without additional reasonably complex limiting circuitry as it is dependent on rotational speed and many many other issues such as 'holding torque' . Any EMF will be from the pole that is being passed and and the design of the stepper as in bipolar or unipolar wired. If you have a standard - say dual pole 4 wire stepper - non geared - stepper you can 'feel the force' shorting a single pole together. You will feel that the stepper is much harder to turn. This is actually a method that is used - certainly by me - to identify unknown pole windings by selecting any of the 4 wires and then shorting 2 together. which ever two causes the turning resistance - the force needed - to turn the stepper is one pole - ie the two wires for a single pole. the other two wires are automatically the other pole. You 'can' also use an led in this case but it is easy to blow the crap out of the led.
Issue 2 is that there is no way to obtain positional data without a feedback potentiometer or Absolute Encoder with the potentiometer being the preferred option.

edit - just a note on ULN type drivers. They are 100% output only as they consist of a Darlington wired pair of bipolar transistors with the final transistor being open collector output. (each channel is the same).
Joe

[Ralph]

Thanks Joe, that's a good explanation.

[Keith Baxter]

Hi,

Thanks for the explanation guys.

I do understand that there is no way of reading the position of the stepper. But I have a feeling that it can be done in Air Manager. Going to need some fancy coding. Let me think on it and do some experimenting.

This is what I love about AM. Always trying to find new ways to hack things.


Keith

[Ralph]

Picking up pulses, if even possible, would be very time critical. I'm not even sure if an Arduino could do that, but you would at least have to do it in an Arduino sketch. The Lua / pin mode isn't quick enough to do that. But as Joe said, I don't think you'll get a reliable result. You're way better of with a potentiometer.

[Keith Baxter]

Ralph,

What I am thinking is using a photo sensor to middle/home the stepper. Then storing the pulse count in a var. That would be the output state. So any time the lock state is not 3 the stepper is activated and driven to home. NOTE: Any time the nose-wheel position is not at "0" then then the tiller cannot be unlocked . This would stop the stepper being it two states. (output or input).

Then when the lock is disabled the drive is disabled (output) and the input (enabled) the var is used. Counting the pulses from the stepper would add/subtract value from the var which would write the value to the dataref.

But reading the EMF pulse is the key. The logic is clear in my mind, but the experiment is going to be the accuracy of the pulse from the stepper.

That is how my mind ticks.
It may never work. But worth a try.



Keith

[jph]

You would HAVE to use a voltage clamping circuit for when the field collapses, probably a pulse stretcher for anti 'ring' pickup and then into a an opto-isolator which would be followed by a buffer - preferably a Schmitt trigger. This would then go to a rising or falling edge detection hardware interrupt routine on the Arduino with Messageport. . Don't forget you would also be only detecting every second step unless you mux or register both A and B poles which would double the circuit above. Even that would only give you around 50 steps per complete arm swing of the tiller presuming 90 degree swing so then you would need to gear the stepper motor with a reduction drive of at least 4 or 5 :1 to get anything close to reasonable resolution.

A potentiometer is 10 cents and can work directly with the arduino and would be perfectly accurate.

A potentiometer looks good to me . Motor drive can be anything as the pot controls the complete position sensing on read or write. It doesn't matter.
Joe.

[Keith Baxter]

You would HAVE to use a voltage clamping circuit for when the field collapses, probably a pulse stretcher for anti 'ring' pickup and then into a an opto-isolator which would be followed by a buffer - preferably a Schmitt trigger. This would then go to a rising or falling edge detection hardware interrupt routine on the Arduino with Messageport.
A potentiometer is 10 cents and can work directly with the arduino and would be perfectly accurate.

A potentiometer looks good to me . Motor drive can be anything as the pot controls the complete position sensing on read or write. It doesn't matter.
Joe.

Joe

I understand your logic and thank you for your input.

My thinking is wonky at best.


Just so I have this clear.
You say use a stepper to drive the tiller to the home position and lock then use a pot to write to the dataref?

I do not see how a pot can return and lock the tiller.

Keith