China A4988 notes

[kb1gtt]

I had decided to try a batch of these A4988 found on ebay. I paid something like $5 for 5 boards, or some crazy low price like that. The boards came with header installed and small heat sinks that had an adhesive back to stick them on the PCB for cooling. Here are my results, and I would suggest paying the extra couple bucks to get OEM boards from Pololu, if you do, it will likely save you hours of head ache.

I'm trying to run these in half step mode, and I've used these before to control small solenoids and such. I'm aware of issues caused by small amounts of contact resistance in the motor leads, which I'm avoiding by doing things like soldering the leads, such that contact resistance doesn't create a tank circuit between the stepper and the capacitive power supply. I'm also aware of issues with the small bulk cap, I have 3 caps at the PCB. A small ceramic for higher frequency stuff, a 100uF per a datasheet, and a 1000uF because I was having some problems. The problems I was having were mostly that the motors were stalling very easily and not upholding the motors speced RPM.

With the china board, I had trouble setting the current limit properly. I could get the 0.56A motor to work OK, but the 1.10A motor would fail to adjust above 0.75A. Which was a bad sign for these chips. After adjusting these, I got the same results on both motors, so the difference in motor load didn't seem to effect the irregularities of these drivers. I then connected a scope to the one channel of the stepper. I was not able to get a good raising and falling transition, they always had some kind of problem, so I do not have a picture of a good wave. Any how, hears what I saw.

However with the same setup and the Pololu board, I was able to adjust the current with no issues at all. I simply adjusted it and it worked. The China boards were quite erratic about how they acted, and I couldn't set them for more than 1.2A, while they should allow up to 2A.

This picture shows several pulses. Notice that each set of pulses is different, I do expect a 50% duty cycle as it does the half step thing. I see it often does not do the PWM half step, as well it often half fires the high side drive.

Stepper_Halfstep_several_pulses.png

This is what I get from the same setup, but with the OEM Pololu board installed. Take note how it turns half on. This board does this consistently, while this was intermittent from the china board, and mostly did not happen.

Stepper_Halfstep_several_pulses_Pololu_board.png

So I zoom in to see what the peak is, and make sure it's below 35V spec, I see it's 19V, so these have not been damaged by over voltage.

Stepper_Halfstep_raise-edge-peak.png

This is what I get from the same setup, but with the OEM Pololu board installed. Not only is this under the spec, it's also ringing any where as much. The blue is the 15V supply showing only the ripple. The yellow is connected to one of the wires that goes to the motor.

Stepper_Halfstep_raise-edge-peak_Pololu_board.png

So what is this occasional high side leakage. It seems like the high side occasional half drives for some reason.

Stepper_Halfstep_wandering-highside-drive-worse2.png

I guess this leakage is normal, but that was not obvious from the china board, as it was intermittent. I'll show current as well as voltage at the end of this post which will show why this wandering happens. Basically it's part of controlling the current in the micro-stepping. This is how the Pololu board looks.

Stepper_Halfstep_wandering-highside-drive_Pololu_board.png

So what about those PWM's, look at the variations. Some with a 5% duty cycle, other with a 50% duty cycle, as well some times it forget to pulse at all, other times it pulses as expected.

Stepper_Halfstep_Poor-raise-edge-PWM-worser.png

And consistently the Pololu board looks like this.

Stepper_Halfstep_raise-edge-PWM_Pololu_board.png

So now that it's working close to correct, I changed the scope a bit. The blue is the 16V ripple, the yellow is 1A on Pololu's schematic, the pink is the current measured on 1A via Rigol clamp, and the purple is 1B.

Several_steps.png

And a closer view.

Partial_step.png

[puff]

could you please make a series of the same screenshots, but with some proper working drivers?

btw, what was the source of those signals for the driver? stm board?
and how exactly you connected the scope? should'nt it be measuring current in the windings?

[kb1gtt]

I plan to do the same when I get the real boards. They arrive about mid week next week, then I think I can get to it the following Monday.

Signal source was a STM32F429 discovery board, the one with LCD. The square wave going to the step pin was very clean, very square.

I installed these boards on a small proto board, with holes and generic copper on the other side. Wires were soldered when ever possible. I connected the scope ground lead to 24- on this proto board. The 12V power supply has a floating output, so the scope GND strap was the only GND reference. Then I connected channel 2 to the 12V signal which is set to AC coupling, and shows the ripple on the top of the screen. Channel 1 was connected at this proto board to a small bit of wire on the proto board. I can post pictures later on, but it's not at arms length right now.

I have a current probe for this scope, I can measure that as well, but didn't bother with that yet. The A4988 is an H-Bridge driver so it's driving to +12 and GND to generate the current. It does not have a current sensor, so it's not modifying it's output signals, it should be driving to high and low, but it's not.

[Abricos]

Check this one ...
It suppose to be better that A4988
toshiba TB6560AHQ
Look at this on eBay http://www.ebay.com/itm/111709001621

[puff]

I"d say 6560 is an overkill here. And we still have some weird problems on a cnc router with that one (3A motor, but just with one axle)
If I don't forget, tomorrow I'll check which drivers are used in my 3d printer. I believe, the power these motors draw won't exceed that of the idle valve motors (i think that was the intended application for that board, wasn't that?)

[kb1gtt]

A nice feature of the TB6560AHQ is that it measure voltage and current of the motor. It could potentially decrease the watts absorbed by the solenoid. As well with a heat sink for $5, that's not a bad price. However it's also kind of large, but it comes with screw terminal which makes it easy to install.

[puff]

I checked, an it is A4988, and it works just nice! Without any soldering - on the same style pins used in the discovery board.
I do remember I had issues with that pot - if you increase the power too much, it tends to overheat, then the heat protection cuts it off for a fraction of a second. If you decrease it way too low, you'll get missed steps. So you need to find the right balance. I'd like to check what current it draws with those small steppers used in 3d printers, but as far as i recall, the torque is okay, although, I don't know how much torque it needs to drive the idle valve...

[kb1gtt]

The pictures posted above were for a motor that was drawing it's rated 0.56A, this driver should be able to do 1A with out a heat sink, I had a heat sink both top and bottom of the chip, no shorting, and it was cool enough to touch with out getting burnt.

[puff]

I'm using A4988 with these motors, with 12V power supply. 1.7A per phase? no issues. could it be you solenoid is faluty?
http://ru.aliexpress.com/store/product/5-PCS-lot-4-lead-Nema-17-Stepper-Motor-42-motor-42BYGH-1-7A-CE-ROSH/822038_862561610.html

[kb1gtt]

In my case the it was connected to a stepper motor, I have two, one that consumes 1.1A and a smaller one that consumes 0.56A. These pumps are brand new from the OEM MFG. Other than pre-mature stalling and me looking at them with a scope to figure out why they are stalling, they operate OK.

One motor is the BA found here
http://www.welco.net/product/wp1000_1100/wp1000_1100_guide/wp1000_1100_guide03.html

The other is the EA found here
http://www.welco.net/product/wpm/wpm_guide/wpm_guide03.html

I would wager a guess that there is no quality control and that other batch's of these PCB's may or may not get the same thing I got in that batch. Some might work, some might not. In my case it appears a bad batch caused a bunch of head ache, and I'm pretty sure that paying $5 more would have prevented the problem. We'll know when I get the other boards and try them out.

[kb1gtt]

First message of this thread has been updated. I finally got to do some testing with the pololu board instead of the China board. I would say the Pololu board is acting much more as expected. First post can be found here. http://rusefi.com/forum/viewtopic.php?f=4&t=1056&p=19378#p19378

[puff]

today I placed an order for a couple of these
http://www.aliexpress.com/snapshot/8012870175.html?orderId=77716718846086
after I watched them on youtube used to drive my idle valve...

[puff]

check this page (google translate might help) - vids and scope pictures are there.
http://mysku.ru/blog/aliexpress/35064.html

[kb1gtt]

Any thoughts about this board https://www.pololu.com/product/2971

I'm thinking the autotune feature and the dynamically reduced current are handy features.

[puff]

for a 6x price. however, if it were not $20+shipping, in absolute values 7$ is absolutely okay. on the other hand, if A3967 or A4988 make the idle valve work the same way, I don't care about the noise.

[puff]

reading the product page for DRV8880:

Warning: This carrier board uses low-ESR ceramic capacitors, which makes it susceptible to destructive LC voltage spikes, especially when using power leads longer than a few inches. Under the right conditions, these spikes can exceed the 50 V maximum voltage rating for the DRV8880 and permanently damage the board, even when the motor supply voltage is as low as 12 V. One way to protect the driver from such spikes is to put a large (at least 47 µF) electrolytic capacitor across motor power (VMOT) and ground somewhere close to the board.

looks like I'll need a sandwich with a proper lower board with mounting holes and capacitors...

Warning: Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver. (More generally, rewiring anything while it is powered is asking for trouble.)

How does this correlate with its protections? (Over-temperature thermal shutdown, over-current shutdown, short circuit protection, and under-voltage lockout)
What is the preferred mode - default 1/8 step or full step?

To set up the current properly, do I need to measure resistance between the coils? Say, it's 50 Ohms. Divide 14.4V power supply by 50 and get 0.288 (A), which is the desired value? The product page states that in order to use microsteps I need the current limit to set lower than the max value to engage the current limit circuitry.


NB!
The ENABLE pin on the DRV8880 enables the driver when high and is pulled up on the carrier. On the A4988 the ENABLE pin enables the driver when low and is pulled down by the carrier.

[kb1gtt]

I suggest, if possible that you use no mechanical connections. If you can have soldered connection to the PCB that's best. If you have a connection some where make sure it's a low contact resistance, and good quality connection.

Your stepper motor is an inductor, which then has some resistance in the wires, connections, ESR in the cap, etc, which is then connected to a capacative circuit. This general topology is commonly known as a tank circuit. Tank circuits are known to oscillate at their resonant frequencies. When it resonates it can amplify the voltages by very large amounts. This resonance issue get's much worse when you have small amounts of resistance. This is why the caps are chosen to be low ESR types. Also take note, that you can get 300V to 600V inside the stepper motor, even when you measure no more than 12V at the driver.

The motor impedance is not the same as your DMM measuring DC resistance. You need to set the current when the driver circuit is functional, as it will be sending pulses to the motor, and this AC signal will have a different resistance than what a DC meter would measure for ohms.

Adjust the current as noted on the Pololu page. You can not adjust it in steady state. They typically include a sensing resistor, and you can typically measure a voltage from a test point on the board, then enter that voltage into an equation provided on that that specific product's page and you have the current. I seem to recall they often have another way to measure the current. Oh, also most of the Chinese versions do not have this test points, so you are left guessing what the proper driver current should be. If you set the current too high, it will cause the stepper motor to get to hot, and perhaps catch fire. If you set it to low, it will skip steps, and have a limited torque. Less steps is easier to get functioning, and more steps is generally smoother. You are probably fine with the default at 1/8 step.

[puff]

This is why the caps are chosen to be low ESR types.

You meant to say higher ESR? (https://www.pololu.com/docs/0J16/all)
Do I have to add electrolytic capacitors to my Frankenstein board, btw?

That pololu page doesn't explain how to determine the needed current. The datasheet from my motor states the winding resistance (impedance?) of 55 Ohms (+/-5 Ohms)

[kb1gtt]

See "current limiting" section of page found here https://www.pololu.com/product/2971

The DC measured resistance has little to do with the current it will see under normal operation. You are best off setting the current by measuring the voltage as noted on the Pololu page. See attached picture. The Chinese drivers typically do not have this VIA which is used for setting the motors current. Setting the current wrong commonly results in electrical fire.

0J7148.1200.jpg

The "Understanding Destructive LC Voltage Spikes" page talks about how you need low ESR for the faster acting energy of the inductive spikes, and you need a larger bulk energy storage to absorb the inductive energy. I see the pololu board includes a 0.47uF low ESR cap, and suggests an external 47uF 50
V or higher V cap be provided by you. If you use a Pololu board, the external cap you provide can be high ESR, or low ESR. It's common that the Chinese boards use a high ESR cap on the board, or they simply remove it to save $, and if you do not have this low ESR cap on the board, it can be destructive to the board or motor. As well if you do not deal with these spikes correctly, they can propagate to the 5V MCU and destroy other circuits. Pololu avoids this common issue by making sure to use a low ESR cap on the board, which allows the ESR of your external cap is not so important. For a Pololu OEM board, what you need high voltage ratings and you need at least 47uF or more for this DRV8880 board. I would try to stay close to the 47uF, but if you have a lager cap, you would probably be fine with that.

[puff]

are you actually reading what's written there?

We introduced the LC transient problem as being unique to ceramic capacitors with low equivalent series resistance (ESR). One particularly straightforward solution to the problem is to add a large capacitor with high ESR to the circuit.

I've seen that video, and there is not a word on how to tell which current you actually need. It is presumed that you know it in advance, beforehand, from the motor specs. But I don't.

[kb1gtt]

I think verbiage is not good for translation. A large capacitor with significantly high voltage ratings will be an aluminum electrolyte style. These aluminum electrolyte caps will have a high ESR relative to the low ESR of a small ceramic capacitor. However keep in mind your small ceramic caps can also have a high ESR like the aluminum electrolyte, but the physical size of the aluminum electrolyte will not allow for an ESR as low as a ceramic cap. Instead of using vague terms like high and low ESR, it would be more clear if they used terms like ESR above blah ohms, or below blah ohms.

If your motor does not specify the allowed current, you can test it by seeing how hot it gets. The current limit is to prevent it from getting to hot. You want as much current as possible, to prevent skipped steps and to get maximum torque, but you do not want the winding's to get too hot. If you adjust it and let it sit for like 30 minutes, you can then measure the outside of the motor. Then you can adjust the current until the temperature is not to hot. However I do not know the thermal constants for how heat gets from the internal wingdings to the outside of your case, and I do not know the allowed temperature of the internal wingdings varnish. So I will have to suggest you simply adjust it until your feel it's not getting to hot. When a motor is provided with a current, it means the manufacture has done this testing and has provided you with a safe current that will not get to hot. To hot is typically based on the winding varnish, and an ambient temperature of 40C. Manufactures typically make a special motor which has a temperature probe, and they know the varnish ratings. They then increase current until they measure the temperature has reached the varnish specified maximum. What ever that current was is what they put on the motor name plate.

Of course Pololu only provides motors which specify the allowed current. It's one of the things you get for that extra couple of dollar. Your Chinese motors commonly don't list this current often cost you lots in labor, or increases your risk of electrical fire.

[Abricos]

[NormanAlphaspeed]

Can anyone tell me if this schematic seems logical? I pretty much cloned the typical application example on the datasheet, but it won't step a thing lol

image.png