Motor driver compatibility

1

Hi everyone,

We want to ude DRV8871 H-bridge driver. The listed continuous current is 2amp and peak current is 3.6amp.

Now, we want to use these motors: 34:1 Metal Gearmotor 25Dx52L mm MP 12V | POLOLU-3228 | Core Electronics Australia

Stall current is either 0.9amp, 2amp, 5amp or 6amp. Should i use these motors with DRV8871 or is it not suitable?

2

Hi Riddhi
The start up inrush current will be about the same as the stall current. Your driver will have to handle this. The driver should be able to handle the stall current anyway or you will destroy it if anything happens to jam the motor.

I would advise against pushing the driver close to rated limits, leave yourself a bit of margin or head room.
Cheers Bob

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3

Hi @Riddhi186182, I agree with Bob. It’s usually best to select a motor with a stall current lower than your driver’s peak current, with a bit of safety-factor in there too.

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4

Thanks @Robert93820 and @Michael

So, if my drivers continuous operation current is 2A and stall current is 3.6A, is it normal practice to use any motor with stall current around 2.5A?

Also, the continuous current of my driver being 2A, do i need to worry that my motor’s no load consumption is only 100mA?

Last on…(hopefully :slight_smile: )…can i use the same driver for brushless motors?

1 Like
5

Hi Riddhi

You driver will have a short (read very short) time capability a bit above continupos operating current but you would be operating pretty close to maximum. I don’t know how much you can trust the specs on this sort of hobby type equipment. They might tend a bit on the optimistic side for marketing purposes.

With this in mind I tend to overcook my requirements and allow as much as 100% headroom. Avoid most problems that way. If you go looking for a motor to suit your driver you stand the chance of not having enough motor power for the job. You may be better off in the long run using a larger driver to suit your motor.

No, The motor will only use the current it needs.

I haven’t got into this with any detail but I think the short answer is NO. Different technology and there seem to be dedicated “brushless” drivers available.
Cheers Bob

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6

Thanks Bob,

Its much clearer to me now. I’ll finalise my motor and then look for the driver. For a professional product deployment, where battery power consumption is an important measure, are there any other drivers that you would suggest? Cost is important as it always is but rates lower as compared to quality and battery life.

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Hi Riddhi186182

That is a better idea. I think the motor itself would be the main contributor to current requirement. That is the advantage of 100% headroom. It leaves room to ignore minor contributors like the driver. But not too many though as they will add up.

You will have to do the same as I would, have a browse. I don’t know off the top of my head.
Be a little bit careful though. I did notice some time ago that some controllers boast something like 15kHz PWM frequency. I think you would be hard pressed to find a motor of any size that would handle this frequency. BUT these are controllers that are controlled by just a potentiometer and generate their own PWM. I think you are generating the PWM with Arduino or similar in which case these drivers do not suit.
Cheers Bob

2 Likes
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Thanks again Bob, much appreciated. Yes, you guessed it right, we’re using CM4.

9

Hi everyone, based on previous advice, I chose motor driver that provides some head room in terms of the stall current. My motor listed stall current is 5amp. My driver TB67H420FTG Dual/Single Motor Driver Carrier TB67H420FTG | POLOLU-2999 | Core Electronics Australia provides stall current of 9amp when only 1 motor is run. Well, that’s my understanding. As per the product details, it appears to me that if i run only 1 motor at a time, the driver provides stall current support of 9amp. I’d appreciate your feedback on whether i am on the right track or reading it wrong.

Also, I have a second very tiny motor for pan/tilt. Now, if I connect my first motor to only only channel, and not both, do I still get the benefit of double the power? Answer is probably no, but thought I will check :slight_smile:

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Hi Riddhi

You are right, the answer is NO. To get an output capability of 9A you connect the 2 outputs together so the device can only support 1 motor if a stall current of 9A is required.

There seems to be a lot of information on the Core site for that product. Read carefully. The initial specs say this but maybe not completely clear.
Quote
"* Output current:

  • up to 1.7 A continuous (4.5 A peak) per motor in dual-channel mode
  • up to 3.4 A continuous (9 A peak) in single-channel mode"
    End Quote

If you look at the pics showing 2 motor and 1 motor connections it will be a lot clearer. They show the single motor connected to both outputs.
Quote
“In single-channel mode, the A+ and A- pins should be connected to form one motor output, and B+ and B- should be connected to form the other.”
End Quote

I don’t follow that and I have not read through in detail. Maybe you have to set single channel mode and that arranges the outputs accordingly. You would have to check this.
Cheers Bob

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11

Hi Riddhi
Excuse my ignorance but just what is “CM4”. I am afraid I am not up with the modern day abbreviations.
Cheers Bob

12

Hi Bob,

If I had to guess I’d assume CM4 was a Compute Module 4 which is a more industrial focussed version of the Raspberry Pi 4 that is optimised towards being embedded in a custom I/O board to host it.
Ideally Riddhi will be able to confirm or correct my guess though.

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Hi Trent
Thanks. Just wondered. If I am interested enough I generally Google these initials to find out what these secret devices are.
Cheers Bob

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@Robert93820 @Trent5487676 - Yes, correct. I meant Compute Module 4 from Raspberry Pi.