DCC controlled stepper motor

[The Nth Degree]

I've been looking at the CT Electronik DCX75 and DCX76. Both include the capability to drive Faulhaber brushless motors, which also require a dedicated driver. Is it possible to take this signal and convert it into a bi-plolar micro-stepping signal? I guess it would involve some sort of processor but would eliminate the need to find a source of the original speed signal decoder, making the whole process slightly easier to achieve.

[Gordon H]

Can't find anything about these that specifically mentions the ability to drive brushless motors, unless it means self-commutating types. Where did you find this reference?

Conventional Faulhaber and similar coreless motors (Maxon etc) simply need a conventional two-wire HF PWM drive.

[The Nth Degree]

Hello Gordon, selected excerpts from CT's website (translated). This is for the DCX76:

 

The decoder DCX76 suitable for all DC and AC motors in the Z-track to H0 locomotives.The maximum total load must not exceed 0.8A.

The mite has in hand a lot less than you can imagine the dimensions themselves.

The high-frequency 16kHz or 32kHz DCX76 provides engine control for Faulhaber motors. Alternatively, there are also infinitely adjustable 30-150 Hz for traditional motors.

Digital or analog operation

[Welly]

I've been looking at the CT Electronik DCX75 and DCX76. Both include the capability to drive Faulhaber brushless motors, which also require a dedicated driver. Is it possible to take this signal and convert it into a bi-plolar micro-stepping signal?

A quick look at the Wiki article :http://en.wikipedia.org/wiki/Brushless_DC_electric_motor suggests "perhaps" but I suspect it won't work for a 2-phase stepper because the drive waveform for a brushless DC motor is more like for the 4 phase stepper except that it is 3 phase!

 

Have you got some kind of driver circuit working the motor yet? - it doesn't have to be small enough to fit the loco and I only suggest this so that you can get to understand it working.

[Nigelcliffe]

Hello Gordon, selected excerpts from CT's website (translated). This is for the DCX76:

 

 

The decoder DCX76 suitable for all DC and AC motors in the Z-track to H0 locomotives.The maximum total load must not exceed 0.8A.

The mite has in hand a lot less than you can imagine the dimensions themselves.

The high-frequency 16kHz or 32kHz DCX76 provides engine control for Faulhaber motors. Alternatively, there are also infinitely adjustable 30-150 Hz for traditional motors.

Digital or analog operation

 

And it means the ordinary DC motors, nothing special. Just the coreless designs which need a high frequency PWM motor drive.

Whilst CT offer vastly better control of small motors when compared to most chips on the market, its not controlling a different type of motor.

 

- Nigel

[The Nth Degree]

Have you got some kind of driver circuit working the motor yet? - it doesn't have to be small enough to fit the loco and I only suggest this so that you can get to understand it working.

Welly, I haven't really got started on the motor yet, it's all just theory at this stage. I'm concentrating - or was! - on my baseboard. Now I've switched my attention to a test loco build in the RMW scratchbuild compo which the motor/driver/DCC will eventually go into.

 

I may try to contact CT directly to see if they have an option or can offer any advice.

[Gordon H]

I doubt whether any manufacturer will have options for driving a stepper motor on a mobile decoder.

You are far more likely to progress with this concept by adapting one of the many DIY decoder designs that have appeared in various places. There is a Yahoo Group called 'selfmade_decoder' where those interested in this kind of thing contribute.

[dergraben]

hello 

 i was very interersted by this thread because  

Im planning to build a magnetic road  with a series of coils activated sequentially by a tree stepper motor driving unit to move magnets on a road 

the three wires would be fed with a repeating sequence + - off / off + -

the speed of the magnet being controlled by the pace of the sequences

 

i wish i could control this process by dcc      In fact  I m looking  for a dcc decoder that could produce on the magnets  the same effects that a classic dcc dc motor decoder produces on a locomotive  ( controls acceleration decelerations and stop)    as i doubt to find a ready to use device to feed and control the coils  How do you think I could achieve the wanted result 

many thanks in advance for your help   patrick 

[sharris]

hello 

 i was very interersted by this thread because  

Im planning to build a magnetic road  with a series of coils activated sequentially by a tree stepper motor driving unit to move magnets on a road 

the three wires would be fed with a repeating sequence + - off / off + -

the speed of the magnet being controlled by the pace of the sequences

 

A timing diagram would be really useful here to show how the sequences on the wires overlap. You say three wires - is it effectively a 4 wire stepper with two of the wired commoned?

[The Nth Degree]

Somewhere in the house I still have these two tiny 6x7mm stepper motors if someone wants to play with them. You can have them for free if you document progress in this thread and use them as I intended – as a controllable drive motor. If all works out and they are usable as drive motors I will contact the supplier to see if I can get more. I'd still like to power my 2mm scale Fox Walkers with them.

 

Let me know here or by PM if you're interested.

Steve

[SHMD]

Steve,

 

Remember my SDB in the 2012 Innovation challenges?

I might just take you up on your offer.

 

 

 

Kev.

[The Nth Degree]

Steve,

 

Remember my SDB in the 2012 Innovation challenges?

I might just take you up on your offer.

 

 

 

Kev.

I do indeed, and you're welcome to them – if I can find the little blighters!

[Suzie]

What drive does a Marklin C-Sinus motor take? Is it similar to a stepper? It might be that a decoder is already available.

[The Nth Degree]

I finally found them. I thought I had a pair, but I have four. I could split them into a couple pairs if more than one person is interested. Same caveat applies to both people, though – show what you do to them in this thread.

 

I got them for a point of sale signage job my company was commissioned to do, but was cancelled for budget reasons. These were free samples, so wouldn't sit well with me to charge for them. The retail value of them is fairly high though.

 

Here they are alongside one of the the locos I was building to put them in.

 

[The Nth Degree]

I just had a look for one to see if they were on sale anywhere. I found a source to get more information on them if you needed:

http://www.aliexpress.com/item/3V-With-Small-Screw-2-Stepper-Motor-Phase-4-Line-6mm-Micro-Motor/1369092332.html?spm=2114.40010208.4.75.jUoZbD

[SHMD]

G'Day Steve,

 

I've been trying to think of an application to use these little motors and I think I have found one.

(They are mainly used in cameras.)

Thanks for the link, by the way, it was that that gave me the idea. (I was trying to find the "step angle" and winding resistance.)

 

But they are NOT expensive! that $23.00, shown on your link, is for 100 pieces! And that is when I came up with an idea.

 

 

As you know, the main disadvantage with these micro steppers is that they :-

 

1/   Will have a large step angle resulting in vibration when it rotates. (So requiring uStepping to smooth things out.)

2/   They will have little torque. (So a gear chain is needed.)

3/   They have a slow RPM - which reduces torque as it increases. (???)

4/   They require "electronics" to drive them. (A Pic uController* - Insert uController of choice here.)

5/   Easy to loose positional accuracy when they stall. (Requires a (software) solution to recover positional accuracy.)

 

Advantages :-

 

1/   They have open-loop positional accuracy. (Once calibrated.)

2/   They are small.

3/   They are very reliable. (No brushes, POTs or switches.)

4/   They are very cheap! ~20p/each in quantities of 100.

 

 

I search more online using the info that your link provided. There are lots of these little motor assemblies and many of them have a leadscrew mechanism built in.

 

So, I think they will make a good cheap low power linear actuator and, if there is enough torque, then they can be used to throw points. (Camera focus mechanisms seem strong enough!)

 

 

So that is what I would like to try - make a point motor to test feasibility and true cost.

 

 

Kev.

[The Nth Degree]

Sounds like a plan! I'll be interested in seeing what you come up with.

 

That's quite an amazing price for such precision engineering.

[dergraben]

Hello I read with interest your thread and different comments 

i wish i could control a 3phase stepper driver with a dcc decoder and looked for some advice links or procedure to achieve such a project many thanks in advance for your help patrick

[Crosland]

What drive does a Marklin C-Sinus motor take? Is it similar to a stepper? It might be that a decoder is already available.

 

Looks a lot like a brushless dc motor to me. Three-phase drive with fixed coils on the stator and magnets on the rotor.

 

Andrew

[SHMD]

Steve, (The Nth Degree),

 

Thanks for your offer but I have bought some online.

(The pricing is unbelievable!)

 

 

Here they are:-

 

 

These cost 12.7p each in packs of 10. Total cost (including shipping and currency conversion into HK dollars) = £2.54p.

These are SMALL. Real small and part of my reason for purchasing them is to not only prove them for model railway use but also to see how smooth, powerful, robust, interfaciable(!), et cetera...   ...or not, as the case may be.

 

(I'm wondering if these little assemblies are about scale, for 4mm, for real point motors!)

 

 

 

These cost much more at 35.3p each in packs of 10. Total cost (including shipping and currency conversion into HK dollars) = £7.06p.

These are quite bigger, than the first set of motors, with more travel, better mounting (and probably) more torque.

 

 

When I get them going, and they do indeed seem promising, I will set a couple of them running - permanently - to see when (and how) they fail.

 

 

Kev.

(I wonder if they will turn up?)

 

[raymw]

I skimmed through this thread, one point noted, the voltage marking of 3V/whatever, may work best if the supply voltage is about 20 times that value - e.g. 60V (at least for the larger steppers I've used). A couple of papers you may find useful - http://yertiz.com/cnc/steppermotor.pdf and more basic explanation http://yertiz.com/cnc/steppers-gecko.pdf from the gecko drivers site. The principles will be the same for the small motors you have. You will be able to drive them simply by using just a Pic, but if you want micro-stepping, then you'll need a few more bits (pun intended).

[SHMD]

Thanks Ray for those links.

I would thoroughly recommend them.

 

They are a good 'single' place where to get most of the basics (theory) from.

(If a little dated now - how many of us have access to "Parallel" ports these days? And no real mention of uController solutions - although, I'll concede, they would be the same as the mentioned "Software Solutions".)

 

Still, there was a thing, or two, in there that I did not already know.

 

 

I am already intending to drive the micro steppers with a higher voltage and will be controlling the current by the open-loop PWM method mentioned. Varying the mark/space ratio, depending upon the over voltage, by use of a simple look-up table, after sampling the supply voltage via the on board ADC.

(I have no intention of trying to uStep them though.)

 

So, plenty to play with try.  

 

 

While driving the Stepper Motor with more voltage (to increase torque at higher RPMs) and limiting the (dangerously high) resultant currents - is a well known technique - I am not sure about the "rule of thumb"(?) figure of 20x Voltage.

 

I would (normally) choose the over voltage level by the factors of :-

1/ the level of electronics complexity required,

2/ the required increase in motor performance, and

3/ the insulation of the Motor Windings.

 

I don't think that the little motors I have sourced (with no data sheets!) will have a very high insulation breakdown voltage.

 

 

Incidentally, I used to design (commercially) large 60V, 5 Phase, 2 A/Ph Stepper Controllers where I used the current sampling driving a Chopper circuit technique - all controlled by a Z80 micro processor! (A long long time ago now...)

 

 

Kev.

[raymw]

fwiw, a few years back I built my own decoders, based on Paul Harman's version http://www.dccdiy.org.uk/motor.html .They work very well, and can be made smaller if needed, but OK as is for 7mm stuff. The page linked shows my pcb design, which can control 4amps, via //op amps, or more if you want to piggy back them. Can also be configured for accessories. If I was bothered, I think I would program the stepper driver directly into the same Pic as the dcc decoding. if iirc, the common pic will sink 20mA on the i/o ports, and you can get away with //ing them up, afaik, so i don't think you'd need any more power components for the small steppers. The big advantage for steppers, is the same as for a reciprocating steam engine - maximum torque when stationary. I expect your little steppers would be OK at anything up to 20V, provided you don't hold on at full power.
But these days, there are better driver chips, for pennies, more or less https://www.pololu.com/product/1182  (or other versions) which would save a load of faffing about.

[SHMD]

Hello I read with interest your thread and different comments 

i wish i could control a 3phase stepper driver with a dcc decoder and looked for some advice links or procedure to achieve such a project many thanks in advance for your help patrick

 

Hi, you will need 1 and a half(!) H-Bridges to drive a 3-Phase stepper motor.

Where did you get the motor and what is your application?

 

 

Kev.

[SHMD]

Motors dispatched but they ain't goin' to be here any time soon!.

 

 

 

Kev.

(I don't normally need an excuse for doing nothing for ages but...)