stepper

[andy_efy]

i am new to the field of robotics. i am planning to make a chassis for which i am deciding on the propolsion system. stepper motors are in my mind. i have learnt that they rotate in steps but i want to know whether there is any way of making them rotate continuosly ?

 

[ericgibbs]

i am new to the field of robotics. i am planning to make a chassis for which i am deciding on the propolsion system. stepper motors are in my mind. i have learnt that they rotate in steps but i want to know whether there is any way of making them rotate continuosly ?

hi Andy,

Basically you control the speed of the stepper motor by sending a continous string of step pulses.
The faster the pulse rate, the faster the motor.
You have to stay within the specification of the motor.

How do plan to control your robot/motors, eg: PIC etc...

Regards

 

[andy_efy]

thanks eric,
i am planning to use a pic. i am using steppers so that i get to calculate the position of the bot without any added circuitry and also to precise movements.....steppers rotate one step for a pilse but suppose the pulse are far enough ( seperation time between pulses is great) then the motor wont rotate continuosly , right? i dont want the bot to move with jerks so is there any solution to this
i am planning to use the bipolar stepper motors found in floppy drives

 

[ericgibbs]

thanks eric,
i am planning to use a pic. i am using steppers so that i get to calculate the position of the bot without any added circuitry and also to precise movements.....steppers rotate one step for a pilse but suppose the pulse are far enough ( seperation time between pulses is great) then the motor wont rotate continuosly , right? i dont want the bot to move with jerks so is there any solution to this
i am planning to use the bipolar stepper motors found in floppy drives

Usually stepper motors dont rotate a full 360 degree/pulse, more like 8deg, 18deg, [ some number that divides equally into 360deg], so that as you step eventually you will rotate 360deg.... got the idea?

The smaller the step/pulse, the smoother the movement.

Some robotics use reversible DC motors for smooth forward and reverse control.

Look thru some of the previous threads on the robotics section.

Hope this helps.

 

[picbits]

Ok - not quite as easy as sending a pulse to the steppers - especially with bi-polar motors.

You need to sequence the coils in an exact sequence to get the steps and direction. On unipolar motors that can be as simple as grounding a common wire(s) and pulsing the remaining wires in sequence.

On Bipolar motors you need to also be able to reverse the potential across the coils so you need something called a H-bridge.

This assumes you want to drive the motors in full step mode (i.e. 1 full step of the motor per pulse). Its much more efficient and smoother to use half step or microstepping - you then get into the problem of having to PWM or chop current to the phases.

Right - if you've got this far without being scared off then don't panic - there are some very very easy ways to sort this.

ST Electronics sell an L297 stepper motor controller and an L298 power H-bridge. With about 5 or 6 external components you can have a controller up and running in half an hour in full and half step mode without worrying about all the crap that goes with it

www.st.com

For a complete tutorial of everything you'll want to know about stepper motors have a lookie here:

https://www.cs.uiowa.edu/~jones/step/

 

[Gaston]

yeah the stepper controler ic makes it nice. i was running a stepper off of a pic but went with the dedicated controller controlled by the pic. it makes life much easier and you free up some of your pins on your pic

 

[andy_efy]

thanks guys,
i am much more confident now and the tutorial was really helpful.will keep you guys informed about any developments

 

[markelectro]

Hello
Does anyone know is I can get a stepper to step in 1,3 or 6 degree??

I want to use them in a project that I have in mind that is clock related.

The stepper would receive either a 1 sec ,30 sec or a 1 min pulse and would be required to work bi-directional.

Regards Mark

 

[picbits]

You can but you'll need to use microstepping.

This varies the current between phases allowing the motor to position itself between steps.

Have a look at www.piclist.com and do a search for microstepping - Roman Black has an excellent microstepper circuit on there.

 

[bloody-orc]

use gears. Works best. Microstepping doesn't always work. Also make sure you have a feedback from the clock "arm" to make sure the stepper actually stepped forwards.

 

[phalanx]

i am using steppers so that i get to calculate the position of the bot without any added circuitry and also to precise movements.....

Just a heads up. You should never rely on the properties of a stepper motor to determine position. There is no guarantee that a stepper motor actually stepped just because you commanded it to do so. You need feedback in the form of a rotary encoder or resolver whose sole purpose is to measure rotational movement.

 

[picbits]

There is a way of determining if the stepper has stepped by analysing the current waveform - missed steps look different to completed steps.

Quite how to do this is a bit beyond me at the moment - I've just finished etching a PCB for a 3 axis stepper motor controller which can give up to 70 volts output at a maximum current of 28 Amps

I think that should be more than enough for my 2.4A/2.2v per phase steppers

I used some Intersil MOSFET driver ICs for driving 4 x IRF540N Mosfet per stepper phase so 8 x Mosfets per motor or 24 for the whole machine.

Good job I have a few tubes of them purchased as surplus

 

[markelectro]

You can but you'll need to use microstepping.

This varies the current between phases allowing the motor to position itself between steps.

Have a look at www.piclist.com and do a search for microstepping - Roman Black has an excellent microstepper circuit on there.

Thaks for that but I was unable to find Romans circuit,could you help.

Regards Mark

 

[picbits]

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