Stepper motor operation
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Thread: Stepper motor operation

  1. #1
    Member
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    Philip E Miner
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    Stepper motor operation

    Before I removed the stepper motor its piston would vibrate at the top of its travel when the ignition was turned on. I then removed the stepper motor and split it apart. The piston seems to slide in the barrel OK. When reassembled the piston remains at the top of its travel, just like before I split it apart.

    According the the nice video from Eugenia (Errol) the piston should move down, uncovering the air holes, then return to its 'home' position.

    Any ideas way mine isn't going down?

    As always, thanks in advance!

    I'll add that the stem of the piston is threaded and that the piston and stem fell out of the bottom half of the assembly. I threaded it back in and stopped when I got resistance. The piston might be able to be screwed in some more, thus physically lowering the piston in the bore, but clearly I don't want to force/break it.
    Last edited by philinnc; 11-09-2020 at 03:25 PM.

  2. #2
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    Quote Originally Posted by philinnc View Post
    Before I removed the stepper motor its piston would vibrate at the top of its travel when the ignition was turned on. I then removed the stepper motor and split it apart. The piston seems to slide in the barrel OK. When reassembled the piston remains at the top of its travel, just like before I split it apart.

    According the the nice video from Eugenia (Errol) the piston should move down, uncovering the air holes, then return to its 'home' position.

    Any ideas way mine isn't going down?

    As always, thanks in advance!

    I'll add that the stem of the piston is threaded and that the piston and stem fell out of the bottom half of the assembly. I threaded it back in and stopped when I got resistance. The piston might be able to be screwed in some more, thus physically lowering the piston in the bore, but clearly I don't want to force/break it.
    Here are photos of mine and one of a new one--note that the distance between the piston and the body is shorter on the new one. It would seem that my piston is 'out' too far. I surmise that when my ignition was turned on the piston didn't move--but the stepper motor did--'unscrewing' the piston.

    Is it a simple matter of screwing the piston in?
    Attached Thumbnails Attached Thumbnails Stepper motor operation-dscn0405-2-.jpg  
    Attached Images Attached Images  

  3. #3
    Senior Member Engenia's Avatar
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    Errol Kowald
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    Quote Originally Posted by philinnc View Post
    Here are photos of mine and one of a new one--note that the distance between the piston and the body is shorter on the new one. It would seem that my piston is 'out' too far. I surmise that when my ignition was turned on the piston didn't move--but the stepper motor did--'unscrewing' the piston.
    Is it a simple matter of screwing the piston in?
    From what I've read, the Walbro ECU treats the stepper differently to the Sagem ECU, so my little video may not reflect what you see.
    That said, the stepper has a groove in the piston shaft that prevents it from turning, so you can not simply screw the piston back in. if you do, you may break that tab that locks it in place.
    If you run the stepper out of it's cylinder it will wind itself out too far and you will not be able to assemble the piston/stepper back into the cylinder. If you find yourself in that situation (as I did), all you need to do, for a Sagem, is to turn the ignition on and press the piston home while the stepper has the piston retracted, holding it rigidly while the stepper tries to push it apart.
    Alternatively, you can buy a stepper controller/driver and move it remotely with that.
    An finally, one of our members in the east of Europe made a cable that reversed the stepper connections, making it run in reverse. So it stepped out first, then reversed to fully retract. Very neat solution. He also has found an alternative source of steppers that are far cheaper and work perfectly with minor changes. I must add this to my list of alternative parts.
    hooroo, Errol www.engenia.com.au [139,200 km - and counting .....]

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  5. #4
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    Quote Originally Posted by philinnc View Post
    Here are photos of mine and one of a new one--note that the distance between the piston and the body is shorter on the new one. It would seem that my piston is 'out' too far. I surmise that when my ignition was turned on the piston didn't move--but the stepper motor did--'unscrewing' the piston.

    Is it a simple matter of screwing the piston in?
    More photos--with the spring and black 'shield' removed the shaft of the piston can be screwed in until the non-threaded portion contacts the stepper motor base. Note that the base has two 'tabs', which (I assume) should receive the two corresponding grooves in the piston's shaft.. If the stepper motor retracted I'm assuming that the piston's shaft would descend into the base, with the tabs in the grooves. But when the stepper motor is energized it only moves 'up', then stops.

    How to get the motor to retract?
    Attached Thumbnails Attached Thumbnails Stepper motor operation-stepper-motor-parts.jpg   Stepper motor operation-stepper-motor-base.jpg   Stepper motor operation-stepper-motor-piston.jpg  

  6. #5
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    Quote Originally Posted by Engenia View Post
    From what I've read, the Walbro ECU treats the stepper differently to the Sagem ECU, so my little video may not reflect what you see.
    That said, the stepper has a groove in the piston shaft that prevents it from turning, so you can not simply screw the piston back in. if you do, you may break that tab that locks it in place.
    If you run the stepper out of it's cylinder it will wind itself out too far and you will not be able to assemble the piston/stepper back into the cylinder. If you find yourself in that situation (as I did), all you need to do, for a Sagem, is to turn the ignition on and press the piston home while the stepper has the piston retracted, holding it rigidly while the stepper tries to push it apart.
    Alternatively, you can buy a stepper controller/driver and move it remotely with that.
    An finally, one of our members in the east of Europe made a cable that reversed the stepper connections, making it run in reverse. So it stepped out first, then reversed to fully retract. Very neat solution. He also has found an alternative source of steppers that are far cheaper and work perfectly with minor changes. I must add this to my list of alternative parts.
    There are four electrical connections to the motor--do you (or the member in Europe) know which ones make it go up and down? It would seem easy to apply 12 volts to the 'down' contacts to draw the piston into the housing. Or is that too naive to believe?

  7. #6
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    Quote Originally Posted by philinnc View Post
    There are four electrical connections to the motor--do you (or the member in Europe) know which ones make it go up and down? It would seem easy to apply 12 volts to the 'down' contacts to draw the piston into the housing. Or is that too naive to believe?
    The Service Manual indicates measuring the resistance between pins 1 and 4 and then 2 and 3. (I did and the resistances are in spec). I then measured the voltage between 1/4, it was +12 volts, while the voltage between 2/3 was -12 volts. I'll apply -12 volts to 2/3 and it should retract. Fingers crossed!

  8. #7
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    Quote Originally Posted by philinnc View Post
    The Service Manual indicates measuring the resistance between pins 1 and 4 and then 2 and 3. (I did and the resistances are in spec). I then measured the voltage between 1/4, it was +12 volts, while the voltage between 2/3 was -12 volts. I'll apply -12 volts to 2/3 and it should retract. Fingers crossed!
    For what it's worth--nothing happened. I applied 12 volts from a spare battery to all combinations of terminals--nothing. I wonder if all four connections must be in place for the motor to operate.

    Such fun!

  9. #8
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    Quote Originally Posted by philinnc View Post
    For what it's worth--nothing happened. I applied 12 volts from a spare battery to all combinations of terminals--nothing. I wonder if all four connections must be in place for the motor to operate.

    Such fun!
    So, using a suggestion from Eugenia (turn the ignition on and press the piston home while the stepper has the piston retracted, holding it rigidly while the stepper tries to push it apart), I did that and enabled the piston to retract to the 'bottom". The air holes were exposed and victory seemed close at hand. But when energized the piston rose--and stopped. And a repeat of holding it produced no repeat action--I believe the plastic threads that grip the piston's shaft are stripped. Oh darn.

    Soo--what is an alternative/cheaper source of a new one? Aliexpress has a Chinese copy for $80 plus shipping.

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    Quote Originally Posted by philinnc View Post
    So, using a suggestion from Eugenia (turn the ignition on and press the piston home while the stepper has the piston retracted, holding it rigidly while the stepper tries to push it apart), I did that and enabled the piston to retract to the 'bottom". The air holes were exposed and victory seemed close at hand. But when energized the piston rose--and stopped. And a repeat of holding it produced no repeat action--I believe the plastic threads that grip the piston's shaft are stripped. Oh darn.

    Soo--what is an alternative/cheaper source of a new one? Aliexpress has a Chinese copy for $80 plus shipping.
    What you have shown is the later Sonecboz Swiss made stepper , it has a green anodised metal piston, part number 7217R059 fitted 2007 onwards TNT, Tre K/ Amazonas.
    This replaced the white plastic piston stepper, which had a habit of both scouring and expanding in the stepper body.
    This "white" stepper is used in all the Triumph triples, part number T1240888, readily available from Mr Triumph your local store.
    Yes, I can confirm the Walbro operates differently to the Sagem as shown in Errols video clip.
    The stepper used in the Fiat Marea 1.6 16v can also be used , top of your stepper with the 3 pipes to the motor on the bottom (Same with the Trumpet one)

    And yes , you have buggered the one you show .

  11. #10
    GBo
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    The stepper motor has 2 sets of windings. It works by firing each winding in sequence but switching polarity as it does it. Not easy to make it work without some electronics. I bought something like this(but not this one) https://www.ebay.co.uk/itm/4-Wire-2-...YAAOSwcN1aZti0 mine only runs at 5v but is enough to run the stepper ok. As Engenia says don’t force it in. The stepper on the Walbro usually runs up to the stop when ignition is turned on and backs down a little. I found my groove had worn so badly my stepper was twitching instead of moving.

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