[kreutz]

!!WARNING!! POTENTIAL CUSTOMER!!! :P

Hello Kreutz, everyone,

this is my fist post in this forum and I would like to show my interest for one of these future board. 4th axis or 3 axis with possibility to upgrade to 4 would be perfect to me.

For now, I think I'm going to buy a bipolar Mechatronic board on ebay from seller "autohec" (how many people uses this one here? any advice? maybe in another thread..), as I am too lazy and too busy to make my own right now.

For a company I co-created 3 years ago that designs and sell FPGA prototyping boards, we used to have our PCB made in China with that company : http://www.goldphoenixpcb.biz, we actually bought their 50-60 dollars "package" on eBay and got a pretty decent amount of boards of really good quality, I think only one or two bare pcb had a flaw amoung the 70-80.
I believe you use a similar company or intend to. For a 10 000 dollars order or so, and if you ship them the components, they can also assemble the boards , for about 1 or 2 cents per solder point, lol!.... but that's a lot of board at once...

Anyway, I'll be glad to follow the updates of that project and will soon post new threads as I have a lot of questions and advices to ask this community as my precision ground ballscrews will be arriving in 1 or 2 days.

Kyromaster

Thank you. I will keep them in mind.

[sdantonio]

Sounds good to me. Is that 48 Max include back EMF or is that 48 max on the power supply?

[kreutz]

Sounds good to me. Is that 48 Max include back EMF or is that 48 max on the power supply?

Those 48 Volt max include BEMF. I was thinking about including a Regenerative Energy Dump feature to the monitoring circuit, but our target prices don't leave an open window to add more features without modifying the price.

[sdantonio]

Those 48 Volt max include BEMF. I was thinking about including a Regenerative Energy Dump feature to the monitoring circuit, but our target prices don't leave an open window to add more features without modifying the price.

Make up a second kit or model (the gecko strategy), have the basic one you propose and then have another that is 25-50 dollars more with the Regenerative Energy Dump feature (if it can be done in that price range).

[kreutz]

Make up a second kit or model (the gecko strategy), have the basic one you propose and then have another that is 25-50 dollars more with the Regenerative Energy Dump feature (if it can be done in that price range).

That is what I am planning, but, due to the complexity of the second one, It will have to be professionally assembled, not sold as a kit. I am planing to include short circuit protection, reverse motor voltage protection, over temperature, over voltage, regenerative energy dump, power supply sequencing and other niceties (possibly midband resonance compensation and mixed decay) in the second one. It won't be a 4 in one board. Probably, they will be offered as individual power boards and one PC/ power interface / monitoring board.

Handling more than 4 Amps per axis (and four axis) in one small board is proving difficult (problems: avoiding ground loops and ground/Vcc noise as well as proper heat distribution)

[kreutz]

I am still working on this design. The schematics are ready and I am working on the first prototype PCB design (1 axis). Meanwhile I made more tests to the "Mardus-Kreutz" unipolar controller board, this time I made a couple of videos showing micro-step accuracy, slow speed and medium range speed tests.

[ger21]

I am still working on this design.

And we're still waiting. Seriously, if you have them ready in June (or even July), I'll be buying one.

[valmet58]

There is definitly a demand for a board of that type..My friend is looking right now for a 4 channel driver board to convert is Milling to CNC..Most of the cheap
boards d'ont go over 3 amps..which is low if you want to drive large steppers....
Hobbyist are always on the look out for good price to quality ratio..
Keep up the good work......

[kiwichris]

Hi kreutz....

What do you mean by 'regenerative energy dump' in terms of stepper motors?

Do you mean loading the motor under deceleration as per regenerative breaking? I assume not, as that dosn't seem to be of much worth for a stepper...

Just curious, havn't heard the term used for steppers before...

Cheers.

[kreutz]

Hi kreutz....

What do you mean by 'regenerative energy dump' in terms of stepper motors?

Do you mean loading the motor under deceleration as per regenerative breaking? I assume not, as that doesn't seem to be of much worth for a stepper...

Just curious, haven't heard the term used for steppers before...

Cheers.

Steppers, like other DC motors, deliver energy to the power supply while decelerating, that energy is accumulated on the power supply capacitors increasing the power supply voltage. Low power steppers at low speeds are not a problem.

During my tests for the "Mardus-Kreutz" unipolar micro-stepper, I found out that, in order to keep the DC voltage almost constant, I needed a fixed bleeder resistor (300 ohm 5 Watt) across the filter capacitor, and my tests were done with only one motor and 35 Volt power supply. (My power supply blew the output capacitors once...before installing the bleeder)

Maybe the end user will never see the need for that, because I am using extreme acceleration and deceleration settings, and also going to extreme speeds the user might never use (like 4000+ rpms). Some people call this regenerative voltage, "BEMF", and specify maximum voltages including it, but that is not the right term.

[kiwichris]

How would you regulate it in a stepper driver? Sense/external shunt on the bridge/rail? Or are you going to manage it via pwm in the bridges in phase with the B-EMF?

It seems you’ll be fighting some diminishing returns on the complexity in the hardware or software, as the phase difference and amplitude will vary for every motor/motion system, and may even vary depending on the position of the machine due to asymmetry of guides, tool loading etc.

Interesting......

[kreutz]

How would you regulate it in a stepper driver? Sense/external shunt on the bridge/rail? Or are you going to manage it via pwm in the bridges in phase with the B-EMF?

It seems you’ll be fighting some diminishing returns on the complexity in the hardware or software, as the phase difference and amplitude will vary for every motor/motion system, and may even vary depending on the position of the machine due to asymmetry of guides, tool loading etc.

Interesting......

I just compare the peak voltage taken from the transformer before the bridge with the DC voltage after filtering, when the last one is bigger than the actual peak voltage (more than 2 volts), I drive a Mosfet to dump the excess energy on a power resistor to ground (I use a 24 volt 150 watt halogen lamp driven by pwm from an At90S2313 instead of the power resistor)

[kiwichris]

OK....

I was thinking about it too much obviously.

You could just look for the large negative pulses on your main shunt resistors, or a PCB trace shunt on the supply input and differential comparator...

So, I suppose this leads to another question: If your drivers and power supply have enough headroom for the higher voltage, is there any other advantage in shunting the extra rail voltage to ground? Or is this just a saving exercise in the component spec for the driver and supply?

[kreutz]

OK....

I was thinking about it too much obviously.

You could just look for the large negative pulses on your main shunt resistors, or a PCB trace shunt on the supply input and differential comparator...

So, I suppose this leads to another question: If your drivers and power supply have enough headroom for the higher voltage, is there any other advantage in shunting the extra rail voltage to ground? Or is this just a saving exercise in the component spec for the driver and supply?

Look at the following oscillogram, it is the Vds of a mosfet switching a 6.8mH stepper motor's coil, the power supply is 35 Volt, Vds maximum is 100 Vdc, The peak transient voltage is 120Volt clamped by the internal drain to source anti-parallel diode's reverse avalanche voltage (IRL540N). Anyone would think that the safety margin between the power supply voltage and Vdsmax is more than enough, and it is not.

Specifying a maximum power supply does not guarantee that a mosfet is going to survive a sudden deceleration due to, lets say a shutdown in another axis' motor, due to over-temperature, while it is moving at high speed. Note that it is not even the problem axis' driver the one that is going to fail. That is why I rather add more complexity and cost in order to save a user's headache and a returned board.

That is an hypothetical scenario, but it is a possibility.

A simple power dump circuit is described in the attached application note. As I told you I use an halogen lamp that is highly an overkill (150W 24 Volt), you won't feel it getting warm. If the mosfet driving it gets shorted You will notice it immediately. I also use a similar circuit to the application note's, driving one interrupt pin on the at90s2313 and controlling the lamp's current by PWM. (I use that at90s2313 already as a safety monitor)

When using integrated bridge drivers it is more uncertain what the safety margin must be, excessive de-rating will create an under-performing driver. A common solution is adding Snubbers, that will be effective if you knew beforehand what motor the user is going to drive, otherwise it is a compromise solution (will work within a range of motor inductances, but can be ineffective in some cases).

[kiwichris]

Is that trace from a bipolar or unipolar drive? I assume Unipolar from the B-EMF spike and ringing after turn-off?

The apparent 58V rail is not such a good look, it's certainly eating up a lot of your headroom.... I assume you don't use a b-emf diode across the winding so that the current will decay quickly?

[Stepper Monkey]

Dumb question, as I am an electronics idiot, but could you stop the BEMF through something as simple as twin diodes to redirect the backfeed? If it needed to dump could it charge a cap on the stepper side of the diode or use a clipper diode or a neon tube or something to regulate? Just go to ground?
I know this is much different and happening much faster than on my vintage bikes, but to keep light bulbs from blowing out from backfeed voltage spikes on my antique motorcycles (Don't ask. The pre-war electrical generation systems are, well, interesting at best) I used a reversed diode clipped to ground that had a breakdown voltage below my bulbs failure point. Spikes just dump to the frame. Would something like this work????

[kreutz]

Is that trace from a bipolar or unipolar drive? I assume Unipolar from the B-EMF spike and ringing after turn-off?

The apparent 58V rail is not such a good look, it's certainly eating up a lot of your headroom.... I assume you don't use a b-emf diode across the winding so that the current will decay quickly?

That trace is from a unipolar drive, nevertheless, the reverse recovery time time of the internal diodes are in the 100s of nanoseconds, so the mosfet switching off time is always less than this time and the spike will be present on a bipolar drive too.

Your suggestion of using a diode across the winding for a unipolar drive is not effective, try it yourself, you won't get much torque from your motor. Clamping the two extremes of the coil to a diode voltage drop will slow down the decay. The recirculation current (on the other half of the coil) will not include ground to Vmotor anymore.

[kreutz]

Dumb question, as I am an electronics idiot, but could you stop the BEMF through something as simple as twin diodes to redirect the backfeed? If it needed to dump could it charge a cap on the stepper side of the diode or use a clipper diode or a neon tube or something to regulate? Just go to ground?
I know this is much different and happening much faster than on my vintage bikes, but to keep light bulbs from blowing out from backfeed voltage spikes on my antique motorcycles (Don't ask. The pre-war electrical generation systems are, well, interesting at best) I used a reversed diode clipped to ground that had a breakdown voltage below my bulbs failure point. Spikes just dump to the frame. Would something like this work????

That is already used, the problem is the mitmatching of switching speeds between the diodes and Mosfets, high transient voltages are created in those nanoseconds.

[kiwichris]

That trace is from a unipolar drive, nevertheless, the reverse recovery time time of the internal diodes are in the 100s of nanoseconds, so the mosfet switching off time is always less than this time and the spike will be present on a bipolar drive too.

The recovery time for the parasitic diode you mean? For fets that have a seperate parallel diode I thought we we're talking 60-90ns?

I assume on a Bipolar drive you'd see the B-EMF spike, but the ringing would be suppressed by the turn-on of the top side fet?

Your suggestion of using a diode across the winding for a unipolar drive is not effective, try it yourself, you won't get much torque from your motor. Clamping the two extremes of the coil to a diode voltage drop will slow down the decay. The recirculation current (on the other half of the coil) will not include ground to Vmotor anymore.

Ay, isn't it amazing how you can miss the point with some things... In the past I've worked on some high current controllers for brushed motors in traction applications where it was an advantage to slow the current decay during PWM off time. I'd seen a couple of low-power stepper app notes using diodes across the windings and just assumed it was the norm with steppers as well...

I've got a simple L/R driver on the bench at the mo, I think some playing is in order....

Out of curiosity, are you using a PC based scope? I've seen a couple of people on here posting what looks like screenshots from a PC. I'm developing tool envy, as I have an old analogue dual trace CRO!

Cheers, Chris H.

[kreutz]

[kiwichris;281234]The recovery time for the parasitic diode you mean? For fets that have a seperate parallel diode I thought we we're talking 60-90ns?

Look at the attached data-sheet, I highlighted some values on Yellow, those values are typical. Toff time for the mosfet depends on gate driving, above 120 ns will increase losses. Typical reverse recovery time for the diodes 190 nS to 290 nS., for integrated bridges like L6203 the diode's reverse recovery time is around 300 nS.

Out of curiosity, are you using a PC based scope?

No, I have two Tektronix scopes: TDS3012B and THS730A. I use the former to document the designs because of the nicer color trace feature.