driving 4 coil 5 wire stepper in both directions

[Simon]

I need to drive a 4 phase (coil) stepper that has 5 wires, my understanding is that I keep the common wire negative (or maybe positive ?) and pulse the coils in the sequency to get the movement I need. To reverse direction I reverse the order i pulse the phases in right ? do I also need to reverse the polarity ?

Basically I need to drive 2 simultaneously in opposite directions so I'm thinking if I put them in parallel with the phases wires up in oposite directions I'll get both moving at the same speeds but in oposite directions.

[Rerouter]

The general convention is tie the center pin to positive, then switch the phases negative with open collector outputs,

as for flipping the phases, i believe you can get away with reversing the polarity of the coils in the second to reveres its direction, allowing them to run in parrellel

just be aware if the load is uneven and exceeds the holding torque of one of the steppers it may miss a step,

equally while moving at faster speeds you can drive the coils with a much higher voltage (current limited) to let them charge up much faster,

[Simon]

flipping phases is easier because they are two motors that need to go in oposite directions to each other by the same amount so if I wire the oposite phases up in parallel I can driver for one and know that the other is doing the same buy in the reverse direction, tight ?

[poorchava]

There are 2 coils inside, each of which has a tap in the middle. In your case taps are connected together. You need to connect common wire to positive supply, and then switch other ends to ground in sequence. If you reverse the sequence, the motor will spin in the opposite direction. It's that simple. Obviously that works only for low speeds, low voltages, low currents etc.

[Andy Watson]

To reverse direction I reverse the order i pulse the phases in right ?

Correct.

do I also need to reverse the polarity ?

No.

Basically I need to drive 2 simultaneously in opposite directions so I'm thinking if I put them in parallel with the phases wires up in oposite directions I'll get both moving at the same speeds but in oposite directions.

Possibly. But if you're thinking about directly wiring the motors in parallel remember that the motors are dynamic systems, they have individual inertias which you will have tied together via an elastic coupling - expect the unexpected in terms of behaviour!  I would, as a minimum use separate drives. Also, as has been pointed out, you will probably want to have independent control of each motor so that you can synchronise their rotation.

[Simon]

Well it's pretty basic, my boss is rebuilding his motorbike speedo, there is the trip mile counter and the main mile counter, they both need to just go round with very low tourge by the same amount but they go in oposite directions. Rather than have a mechanical solution he wants to just couple two small stepper motors to each and drive them in reverse directions.

So wait, I have 2 forward and 2 backward coils in each ? or am I having to drive one negative at any time ? I'm hoping to do all of this off +5V

[Andy Watson]

Ah, I see.  It might work

So wait, I have 2 forward and 2 backward coils in each ? or am I having to drive one negative at any time ? I'm hoping to do all of this off +5V

With a 4 coil, 5 wire motor the arrangement is almost certainly as Rerouter has described, i.e. the fifth wire is effectively the centre tap of two opposing coils. But, you're over thinking this. Consider the coils as separate entities in which you have to attract the magnet in sequence to the next coil by energising that coil. Provided the polarity is consistent, all you have to worry about is the sequence of energising. Note you only have swap-over the two of the four wires to reverse the sequence.

[Simon]

ok so it's how I thought (I think) I just pulse round in a circle, and yes that would put 2 out of 4 in the same place at 0 and 180 degrees

[poorchava]

You have two coils, but they are wound in such a way, that when current comes in from the center tap, to one end it creates magnetic flux in one direction, if you connect the other end to ground it creates opposite flux. So by alternatively connecting ends of a center tapped coil you can cause the coil to either attract or repulse to the permanent magnet on the rotor. By doing it in alternating fashion on both coils you can make motor move around.

[Simon]

so I have 2 sets of 2 coils with a centre tap that all share the centre tap connection ?

[Andy Watson]

Yes.

[Simon]

so I couls drive 1 coil posisitive and one 180 degrees oposite negative to get more power ?

[SeanB]

Don't overthink this Simon, as it is a speedo drive and you are going to try to get to 300-500RPM abs max you are likely looking at using small 5V stepper drives out of a old disk drive unit, and just use them to drive the shafts directly. They will work as you start up at slow speed and go down at a slow speed ( relatively to the ability of the max rating of the drives) so you just need a counter to give the required 4 pulse rotation rate driven from the speed pick up unit. No need for a MCU here just simple combination logic. Might miss pulses at high speed and might slip a bit if he puts the grip to full welly from a dead stop but should be workable.

[Simon]

Well he is choosing the motors as he needs to make it work mechanically. He has found a switec needle pointer motor that works nicely for the speedo, the logic for the mile counters is that so long as they catch up eventually.

Don't forget I need to read the timing from the pickup for the speedo so i need an mcu, the arduino should work well, we found a library written for switec motors so it takes the headache out of worrying about positioning the speedo needle and the mile counters can just play catch up between readings.