How to cool down a stepper motor?

[gimpo]

If you really need to cool your stepper motor for instance because the ambient temperature is too high then you can add a watercooled coolingplate to the flange of the stepper.

Thanks for the advice, but all the construction would look a little bit too bulky and massive. I try to keep things as small and slim as possible.

[gimpo]

Spend some serious time studying the Trinamic data sheets to get an idea of what these controllers offer, they are the most advanced stepper motor controllers I am aware of.

Time is what I need the more.
I feel acquainted in dealing with "simple" technology, but I will do what you suggest if I will be able to delay my project of around two months.

[innkeeper]

how hot is it getting that makes you concerned??

[gimpo]

After 10 minutes with windings fully powered (around 1.3A) I could barely touch the surface of the motor. This is normal, but at the same time I started to be worry.
As I wrote above, this "thing" should be installed on a motorcycle. I started to imagine the motorcycle parked under the sun in an hot sunny day of August. It will take a while before the stepper get cooled by the wind after starting the motorcycle and driving.
I will try to avoid to an enclosing black box too, but in any case reducing the current when not necessary will be a big benefit and will help me to stay on the safe side.

P.S.
As reported above, I ordered a cheap IR thermometer to have a rough idea of the temperatures. But I'm still waiting for the delivery.

[langwadt]

If I put a resistor between TPI and ground (i.e. the pin of Arduino set to LOW), then it will be in parallel with the resistor of the potentiometer (10K).
So I think that a value of 50K for such resistor (R_ref) should lower the voltage of circa 16-20%, and the same should hold for the current.
Or I missed something?

(Attachment Link)

the reduction will depend on the pot setting but it'll work.

Add a capacitor on Vref and you can use PWM to vary the current

[gimpo]

the reduction will depend on the pot setting but it'll work.

Yes, I have to detect the resistance of the pot when set at my preferred position, then I can calculate the right size of the resistor to be used in parallel  with it.

Add a capacitor on Vref and you can use PWM to vary the current

Intriguing. But as I know a cap can act as a filter if not correctly sized. I'm using an . It is not immediate for me what size of the cap I should use (Arduino Pro Mini at 3.3V with 490 Hz of PWM frequency).

I can recall my vague reminiscences have brought to my mind the τ=RC constant to calculate the charging/discharging time, but not resistor here... 

[langwadt]

the reduction will depend on the pot setting but it'll work.

Yes, I have to detect the resistance of the pot when set at my preferred position, then I can calculate the right size of the resistor to be used in parallel  with it.

Add a capacitor on Vref and you can use PWM to vary the current

Intriguing. But as I know a cap can act as a filter if not correctly sized. I'm using an . It is not immediate for me what size of the cap I should use (Arduino Pro Mini at 3.3V with 490 Hz of PWM frequency).

I can recall my vague reminiscences have brought to my mind the τ=RC constant to calculate the charging/discharging time, but not resistor here... 

start with something like 1u, it's not too critical all it has to do it turn pwm into roughly DC

[gimpo]

The "BigEasyDriver Manual" states
"A Vref of 1.76V will result in a motor current of 2A." (per winding - my note)

The output voltage of the Arduino pin could be set (roughly) to any value between 0V and +3.3V by using PWM.

If I understood right, I should be able to lower a little the Vref voltage upon my needs by connecting an output PWM-pin of Arduino to the Vref pin via a small cap.
SO, let's say that I would lower the voltage from 1.76V to 1.3V. Then (if your idea works) all I need to do is simply  to choose the right duty-cycle for that value. It is correct?

[langwadt]

The "BigEasyDriver Manual" states
"A Vref of 1.76V will result in a motor current of 2A." (per winding - my note)

The output voltage of the Arduino pin could be set (roughly) to any value between 0V and +3.3V by using PWM.

If I understood right, I should be able to lower a little the Vref voltage upon my needs by connecting an output PWM-pin of Arduino to the Vref pin via a small cap.
SO, let's say that I would lower the voltage from 1.76V to 1.3V. Then (if your idea works) all I need to do is simply  to choose the right duty-cycle for that value. It is correct?

cap goes from Vref to ground, resistor from Arduino to Vref

[gimpo]

Ah!
So the R_ref resistor is still. So you're proposing a Low-pass RC filter (see attached image). Why?

[langwadt]

Ah!
So the R_ref resistor is still. So you're proposing a Low-pass RC filter (see attached image). Why?
(Attachment Link)

the lowpass turns the pwm into the DC voltage need for Vref

the stepper controller itself does the current control by turning off the outputs off for a while when the voltage across the 0.22R current sense resistors
exceeds the Vref voltage (divided by 4)

[gimpo]

Uh!. So that is useful for smoothing the PWM output. Nice.

Anyway, I got a little bit lost...
To summarize, let's suppose that I get my 1.5A for my stepper when Vref = 1.5 V.
Then:

1. PWM output = ~1.5 V (to make the Big Easy driver working normally)
2. PWM output = 0V (to lower the Vref)

In the case 1, the R_ref does not influences the voltage. In case 2 the same resistor works in parallel with the pot and lower the voltage. Is this right?

[langwadt]

Uh!. So that is useful for smoothing the PWM output. Nice.

Anyway, I got a little bit lost...
To summarize, let's suppose that I get my 1.5A for my stepper when Vref = 1.5 V.
Then:

1. PWM output = ~1.5 V (to make the Big Easy driver working normally)
2. PWM output = 0V (to lower the Vref)

In the case 1, the R_ref does not influences the voltage. In case 2 the same resistor works in parallel with the pot and lower the voltage. Is this right?

just try it and measure the resulting voltage on Vref for various PWM values

[gimpo]

 

[innkeeper]

After 10 minutes with windings fully powered (around 1.3A) I could barely touch the surface of the motor. This is normal, but at the same time I started to be worry.
As I wrote above, this "thing" should be installed on a motorcycle. I started to imagine the motorcycle parked under the sun in an hot sunny day of August. It will take a while before the stepper get cooled by the wind after starting the motorcycle and driving.
I will try to avoid to an enclosing black box too, but in any case reducing the current when not necessary will be a big benefit and will help me to stay on the safe side.

P.S.
As reported above, I ordered a cheap IR thermometer to have a rough idea of the temperatures. But I'm still waiting for the delivery.

yes steepers get hot enough to burn you ... that is normal...

typical nema 17 steppers are rated for 80 °C above ambient and a max temp of 130 C  ... so if it's 40C outside your talking about 120 C ... so u less your getting over a 80 C rise or its getting over 130 C, then you have noting to be concerned about.

i would not enclose it in anything plastic or unventilated.

not sure why you would lower the current at any point unless your not using them at all and shutting them down completely if they're not needed ..... when you reduce current you reduce hold power so thats something to consider. 

do make sure you're not operating the stepper over the current as that will overheat them. the major damage to overheating them is 2 fold, one it will reduce the strength of the magnets permanently reducing the strength of the stepper, and second, it can melt the plastic inside the stepper and burn windings. 

[gimpo]

Hi innkeeper,

thanks for your observations. As I stated many posts above, I just want to have some safety margin to stay on the safe side. A reduction around 20% of torque when the stepper is holding a load (no movements) is not a bad idea, after all. If I can do it by program is even more clever.

More than this, I had another idea while writing in this thread: this feature could be used to make the manual rotation of the throttle (yes, we're talking about a motorcycle) more effortless. The stepper could help the hand of driver once the direction of the movement is detect.
I have received a little board with an AS5600 magnetic sensor rated for 0.015 degree of resolution (in ideal conditions). So I think that I could detect when the "user" starts manually applying some force on the motor shaft, and help him with some light torque in the same direction. It would be clever if this idea works, isn't it? 

Anyway, having (even a limited) control on the current trasmitted to the motor is a "nice-to-have" feature that all driver should offer, IMO. Setting the current by manually rotating a pot seems a little as a travel back to the '80 era... 

The enclosing box
Yes, I have to avoid a plastic in favour of a 100% metal solution. With some thermal paste in between, a metal box could work as heat sink as well.
I have also thought to mount the stepper at open-air, but the look will be honestly quite ugly... 

The electronics will be stored in a separate box 90cm (3 feet) away from the stepper. I plane to use a generous size of the cables to minimize resistance. I think that some AWG20 wires should be enough.

[gimpo]

UPDATE

In the meanwhile I almost randomly discovered another driver board distributed by Pololu: the TB67S249FTG board.

By scrolling down in the page until the "Active Control Gain" paragraph, I have found that this driver can "automatically" reduce the current when no high-torque is required. The amount of this reduction can be set by using two pins on the board.
No idea if this feature works in the real life and can reduce the temperature when the motor is stationary, but seems so: https://youtu.be/sySdiGsw9-g

[innkeeper]

that's a pretty cool find, id definitely give it a try if I were you.