Feathertouch focuser motor controller issues...

[SkyBound]

Hi all,

i have a couple of questions, and I will try to explain as best I can.

i have a 2" Feathertouch crayford focuser on the back of my SCT, and it is superb, I also have the starizona dedicated motor and controller for said focuser, now these motors are a 5v motor and the starizona comtroller supplys 5v output to the motor as it should, BUT, there is not reallly enough torque for my imaging kit from the motor. That is my first issue

So I bought a stepper controller form Hitecastro for another motor, but also to be tried with this one,  when I bought I told them it was also going to be used with a starizona motor which was 5v and there controller is a 12v one, so they said no problem, we supply a 12v to 5v Adapter using resistors, so I thought great, when it came I tried it and wow what a difference it was superb, loads of torque far better than the starizona controller.....but why, it seems to me that the motor is getting more than 5v (which I assume is the reason for more torque) even though I am using the supplied 12v to 5v Adapter....so why would this be happening ??and will it cause any problems in the long run ?? the motor sounds a tad louder, which I ssume is because of the extra voltage...??

the 12v to 5v Adapter consists of 1 x 10W 100 ohm resistor and 4 x 5W 100 ohm resistors as there are five wires used, for the controller.

when I checked the voltage at the output of the adapter it showed 12v......so how does this resistor 12v to 5v Adapter work....as the motor does not seem to get 12v when running but gets more than the 5v it should do.....which seems odd, but it seems to work really well....I reckon it's getting around 7-9v (certainly more than 5v but a lot less than 12v)  but that is just a guess, but my real issue is that this set up works perfectly whereas the proper 5v starizona controller is, well basically rubbish and only really works with just a diagonal and eyepiece, with my camera and filter wheel it is just a no go, it stalls, or slips....so why and how does anybody use the starizona controller with this motor when imaging....??

and thoughts from any of your DIY guys out there, and can all this be explained to me in laments terms...??

 

[Dr_Ju_ju]

It's not about voltage, it's about how much current can be passed through the motor, before it gets too hot, so you've bought a current limiting resistor set.

If the driver is based on one of the standard chipsets (DRV4498 etc.) then a reference voltage can bet set, that limits the amount of current that is supplied to the motor...

[SkyBound]

2 hours ago, Dr_Ju_ju said:

It's not about voltage, it's about how much current can be passed through the motor, before it gets too hot, so you've bought a current limiting resistor set.

If the driver is based on one of the standard chipsets (DRV4498 etc.) then a reference voltage can bet set, that limits the amount of current that is supplied to the motor...

Thanks for the reply but am a little puzzled So please forgive my ignorance here :), are you saying that it's ok for the motor to be receiving more than 5v as long as the current is limited, which you say it is with my Adapter I bought from Hitecastro ??

and not quite sure what you mean by setting a reference voltage....? And what the driver DRV4498 is...??

i just don't understand how Starizona can be selling theses controllers for there motors, that supply the 5v when it just does not work and has no grunt at all to do the job......and yet a third party controller works superbly albeit at a higher voltage 

[SkyBound]

3 hours ago, Dr_Ju_ju said:

It's not about voltage, it's about how much current can be passed through the motor, before it gets too hot, so you've bought a current limiting resistor set.

If the driver is based on one of the standard chipsets (DRV4498 etc.) then a reference voltage can bet set, that limits the amount of current that is supplied to the motor...

Also I was under the impression that motors would only draw the current it needed, so why limit it...? I thought it was the voltage that had to be correct and not over or it could burn out.....

it all really confusing my small brain..

[Dr_Ju_ju]

Sorry if this is going to be a bit heavy....

Stepper motors are driven by individual step pulses. These step pulses are usually generated using some form of motor driver (e.g.  a commonly used device is the DRV8825 http://www.ti.com/lit/ds/symlink/drv8825.pdf) which in itself is usually driven but some sort of processing control, albeit very small. This control may then have additional connection(s) e.g. USB, so that it may be controllable from a PC.

 Have a look at this thread, which my give you a greater insight

 

[SkyBound]

3 hours ago, Dr_Ju_ju said:

Sorry if this is going to be a bit heavy....

Stepper motors are driven by individual step pulses. These step pulses are usually generated using some form of motor driver (e.g.  a commonly used device is the DRV8825 http://www.ti.com/lit/ds/symlink/drv8825.pdf) which in itself is usually driven but some sort of processing control, albeit very small. This control may then have additional connection(s) e.g. USB, so that it may be controllable from a PC.

 Have a look at this thread, which my give you a greater insight

 

Hi, thanks for that but does not really answer my initial questions....

Still trying to figure out why it works better with a different controller at a higher voltage, and why it can't just draw the power it needs...and why you say I have a current limiting Adapter.....!!

my logic tells me it should work perfectly with the proper controller, yet it does not...?

[Gina]

Stepper motors are best current driven and this is what the proper drivers such as the A4988 do.  The motors are inductive and the extra voltage with controlled current will drive them much better.  Simple voltage drive such as produced by the ULN2003A or similar is alright for full stepping but you really want current drive for micro-stepping.  A focuser drive will often use voltage mode to save cost and allow a lower voltage supply.  If you use a higher voltage than specified, resistors will safely limit the current and stop overheating and, as you found, can produce more torque without overloading the motor.  It's fine

[SkyBound]

4 hours ago, Gina said:

Stepper motors are best current driven and this is what the proper drivers such as the A4988 do.  The motors are inductive and the extra voltage with controlled current will drive them much better.  Simple voltage drive such as produced by the ULN2003A or similar is alright for full stepping but you really want current drive for micro-stepping.  A focuser drive will often use voltage mode to save cost and allow a lower voltage supply.  If you use a higher voltage than specified, resistors will safely limit the current and stop overheating and, as you found, can produce more torque without overloading the motor.  It's fine

Thank you very much Gina, really appreciate that reply, and am glad you understood what I was asking as I don't think I made it too clear... so the controller I am now using from Hitecastro with the 12v to 5v resistor pack Adapter, which they also supplied with it, is not really controlling the voltage then, more so the current...? Have I got that correct, and that's why it works much better than the proper starizona one (which is very expensive too) that is purely limited to sending 5v to the motor...??

[Gina]

Absolutely correct - yes

[SkyBound]

44 minutes ago, Gina said:

Absolutely correct - yes

I am amazed that anyone finds the starizona or Feathertouch controllers useable, as they work just about OK, with no weight on the focuser, with maybe a diagonal and small eyepiece, but with any sort of camera they are useless....

i have also tested the motor using a 5v supply through the Hitecastro controller and not using the resistor pack Adapter, and again its useless....so the problem is with the voltage...and yet the motors are a 5v rated Nippon stepper motor, so seems really ridiculous that to get them to work properly you have to use 12v and control the current....  or maybe they are not designed for using on an imaging rig..

[Gina]

Motors used in 3D printers are mostly rated at around 3v yet the motor supply to the A4988 driver is 12v (or even 17v in some cases).

[SkyBound]

The starizona and Feathertouch controllers are powered by 12v but i have checked at the output plug to the motor and its 5v there, so the 12v must be regulated down to 5v....

so wouldn't that be the same for your 3D printer motors, regulated down to 3v...? Or do you think that they get a higher voltage and have the current regulated...? If so then starizona and Feathertouch should re design there controllers that way....especially at the price they are, I am quite annoyed at what I paid for it, and does not do the job and is not fit for purpose in my opinion...

[Gina]

No, the A4988 and similar drivers don't regulate the voltage, they work on the current, having a resistor in the drive to each coil where the voltage across each resistor is compared with a reference voltage set with a tiny potentiometer.  More information HERE

[Gina]

If you think the product you have bought is "not fit for purpose" and it isn't too long since you bought it you should be able to return it for either a different product or a refund under the Sale of Goods Act and/or The Distance Selling Act if you buy from the 'net.  But you seem to have found a satisfactory answer in this case.

[SkyBound]

20 minutes ago, Gina said:

No, the A4988 and similar drivers don't regulate the voltage, they work on the current, having a resistor in the drive to each coil where the voltage across each resistor is compared with a reference voltage set with a tiny potentiometer.  More information HERE

This paragraph below, from the link you sent explains it really, so thanks very much for that, 

so the 100 ohm resistors in my resistor pack are limiting the current to under a certain amount, because it is being powered by a 12v supply to a 5v motor...there are 5 of these in the resistor pack, one to each wire of the motor..does that sound correct..??

and as the Feathertouch and starizona controllers only do full and half step, maybe that's why they just use voltage limiting controllers..!

 

To achieve high step rates, the motor supply is typically much higher than would be permissible without active current limiting. For instance, a typical stepper motor might have a maximum current rating of 1 A with a 5Ω coil resistance, which would indicate a maximum motor supply of 5 V. Using such a motor with 12 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.

 

[Gina]

With 5 wires it sounds like the motor is a unipolar type with the coils centre tapped and this becomes the supply with the other 4 wires being the coil ends and these are connected to 0v in sequence to form the drive.  It's possible that the intention is to put a resistor in each wire but I'm not sure - how are you using them?  You seem to have found a satisfactory arrangement and I suggest you just carry on with that.  I would have expected to have resistors in just the 4 wires that connect to the ends of the coils but not knowing the motor details I can't tell.

In my DIY focus controllers I use unipolar motors with 5 wires and ULN2003AN driver chip (these are a set of 7 Darlington transistors with overvoltage diodes built in to catch the back EMF from the inductance) driven by an Arduino Nano.  This is a very cheap alternative to commercial units if you can handle a soldering iron.  There are many designs around as well as mine including a full ASCOM version by "tekkydave" in this forum.

 

[SkyBound]

1 hour ago, Gina said:

With 5 wires it sounds like the motor is a unipolar type with the coils centre tapped and this becomes the supply with the other 4 wires being the coil ends and these are connected to 0v in sequence to form the drive.  It's possible that the intention is to put a resistor in each wire but I'm not sure - how are you using them?  You seem to have found a satisfactory arrangement and I suggest you just carry on with that.  I would have expected to have resistors in just the 4 wires that connect to the ends of the coils but not knowing the motor details I can't tell.

In my DIY focus controllers I use unipolar motors with 5 wires and ULN2003AN driver chip (these are a set of 7 Darlington transistors with overvoltage diodes built in to catch the back EMF from the inductance) driven by an Arduino Nano.  This is a very cheap alternative to commercial units if you can handle a soldering iron.  There are many designs around as well as mine including a full ASCOM version by "tekkydave" in this forum.

 

There is actually 6 wires, but two of them are joined which I assume is the supply voltage, and five resistors, 4x5w 100 ohm, and 1x10w 100ohm connected to the two joined wires, I guess there is more heat to get rid of on these joined wires hence the larger resistor.

that is how  it came from Hitecastro, it connects to the output of there stepper controller, and then a  cable from the other end to my motor,  it works really well....