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### Topic: Motor acceleration speed (Read 3224 times)previous topic - next topic

#### Yaro

##### Aug 09, 2013, 04:27 pm
How I can measure motor acceleration? I have this specifics:

The torque necessary to start rotate my object(overcome the static friction) is 172+gf at 28mm.
The torque necessary to overcome the dynamic friction is less then 100gf at 28mm.

I see the holding torque is much more then static friction, so it'll rotate without problems.
Now I know the forces that I need to beat, how I can calculate motor acceleration without weight, with weight and motor efficency vs. torque?
Also, acceleration depend to motor driver hardware? Chep motor driver will affect acceleration?

p.s. I need to complete a 90° rotation withing 130ms

Thank you.

#### icio

#1
##### Aug 10, 2013, 10:51 am
With stepper driver we can start ramp with 1000 step/sec , ( 1msec/step) as you can rotate 90 degreed in 100msec at half-step , full current, bipolar driving, 24volts power supply and chopper method. You must pay attention to elastic return when press chuck onto object because if can't detect force on object it's easy go overall max motor torque.

#### Robin2

#2
##### Aug 10, 2013, 11:42 am
I'm thinking of getting some stepper motors for a project so I'm interested in this.

@Yaro, can you explain why you need to know the acceleration? Are you concerned about how quickly the motor will get up to speed without losing count of the steps?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### Yaro

#3
##### Aug 10, 2013, 03:26 pm

With stepper driver we can start ramp with 1000 step/sec , ( 1msec/step) as you can rotate 90 degreed in 100msec at half-step , full current, bipolar driving, 24volts power supply and chopper method. You must pay attention to elastic return when press chuck onto object because if can't detect force on object it's easy go overall max motor torque.

I can't understand, why i can start with 1000 step/sec and not more? It's related to motor or driver?
This motor have rated voltage of 3,1v, i think it'll burn. What mean half-step? Also what is chopper method?

I'm thinking of getting some stepper motors for a project so I'm interested in this.

@Yaro, can you explain why you need to know the acceleration? Are you concerned about how quickly the motor will get up to speed without losing count of the steps?

...R

I'm not looking for extreme precision, but for high speed. I need to rotate an object that opposes the movement with friction, so i need to calculate torque necessary to rotate it and the torque necessary to rotate mechanical gripper(that have it's weight). I have the approximate time within i need to complete 90° rotation(130ms or less). Now i need to choose motor that fit this specifics.

I found different motors with high torque, but I need to know if I can rotate them with a high acceleration, doesn't matter rpm if the motors have very slow acceleration and i don't need to do complete rotations.

#### icio

#4
##### Aug 10, 2013, 05:53 pm
Your choice about kind of motor is right,  to increase performance in stepper motor driving you must give higher voltage and stabilize current with chopper method:

http://en.wikipedia.org/wiki/Stepper_motor  at  paragrhaph: "chopper drive circuit"

1000step/sec is maximun start step/rate with max torque without losing steps

http://electronics.stackexchange.com/questions/31143/how-to-determine-velocity-profile-for-two-stepper-motor-in-robot-driving

the ramp can start from 1000step/sec and going to 3000-5000 step/sec but  with such a small rotation of only 100 steps (90 degreed) you haven't need to perform start and stop ramps

If you make power supply of only 4volts without chopper   instead 24v with chopper   the maximun start step/rate is only 100step/sec

#### Robin2

#5
##### Aug 10, 2013, 08:23 pm
The implication of starting at 1000 steps per second is that the motor can instantaneously go from standstill to 300 rpm without losing steps. Is that true, or am I misinterpreting something?

Also I would expect that it couldn't get up to speed so quickly if it had a heavy load on it? How does one know (or find out) what is the relationship between startup speed and load?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### jackrae

#6
##### Aug 11, 2013, 08:13 pm

http://en.wikipedia.org/wiki/Inertia

Objects with mass all tend to prevent any change of motion (resist acceleration/deceleration)

So trying to accelerate a mass from rest to high speed will take both time and energy, irrespective of whether or not you apply "X" pulses.  If inertial forces are greater than rotational forces, the motor will slip (lose correlation between pulses and actual position)

#### Robin2

#7
##### Aug 11, 2013, 08:31 pm
Which "you" are your referring to. I understand inertia and that is why I posed the questions. Do you, @jackrae, have any code examples that show how to take account of inertia with stepper motors?

...R

Two or three hours spent thinking and reading documentation solves most programming problems.

#### jackrae

#8
##### Aug 11, 2013, 09:31 pm
The you you

"Now I know the forces that I need to beat, how I can calculate motor acceleration without weight, with weight and motor efficency vs. torque?
Also, acceleration depend to motor driver hardware? Chep motor driver will affect acceleration?

p.s. I need to complete a 90° rotation withing 130ms"

But you made no reference as to what "weight" meant and you didn't refer to possible inertial reactions so I presumed (obviously wrongly) you weren't taking inertia into account.

Ah well ...... =(

#### Robin2

#9
##### Aug 12, 2013, 09:31 am
@jackrae, the "you" that you quote isn't me it's @Yaro. Please be more careful and more precise.

And you didn't answer my question about whether have any code examples that show how to take account of inertia with stepper motors?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### jackrae

#10
##### Aug 12, 2013, 10:16 am
But you said you were interested in the question so presumably you are also interested in the potential problems of accelerating masses

I don't have any code to illustrate accounting for inertia

Although inertial forces are a linear function, the forces driving a stepper motor (pulses) are not  -  the motor either steps in accordance with the applied pulses or it "misses a beat" (due to inertial forces being greater than the driving forces).  Providing the driving force (pulses) remain acting they will eventually overcome inertial forces but the stepper will be out of sequence with the actual number of driven steps.  Similarly when decelerating, if the inertial mass is great enough, lack of motor driving pulses will not necessarily cause immediate stoppage of the motor.

The mathematics could become quite complicated (since they will probably involve discontinuous non-linear variables) and a simpler solution might well be the conducting of empirical tests to establish system performance under actual operating conditions.

#### Robin2

#11
##### Aug 12, 2013, 12:31 pm
Thank you @jackrae

I had hoped that readers would have inferred from my questions that I was somewhat sceptical.

It would be nice to make contact with someone who has built and programmed a useful machine.

For the benefit of others I turned up a lot of useful information by Googling "stepper motor selection"

...R

But you said you were interested in the question so presumably you are also interested in the potential problems of accelerating masses
Two or three hours spent thinking and reading documentation solves most programming problems.

#### MarkT

#12
##### Aug 12, 2013, 10:36 pm

How I can measure motor acceleration? I have this specifics:

First step convert all the units to S.I.!
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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