torque of a stepper motor

[Nigel Goodwin]

oh.. then i will think abou that... to increase the voltage... and what is a " switch-mode inverter"??

It converts the DC to high frequency AC, transforms it up using a small transformer, then rectifies it to give a higher voltage DC. For moderate voltage increases you can use a choke rather than an inductor.

But first, I would suggest trying an external supply to see how much you need to get the torque you're looking for, don't forget to use either current limiting resistors or PWM to restrict the current.

 

[bananasiong]

okay... thanks.. i will try to increase the batteries first..

and.. about the switch mode inverter.. is it an IC? is it very expensive thing? i really know nothing about that..

 

[Nigel Goodwin]

okay... thanks.. i will try to increase the batteries first..

and.. about the switch mode inverter.. is it an IC? is it very expensive thing? i really know nothing about that..

You can get IC's, but they generally still need plenty of support parts, it's NOT a simple design - in any case, what are you doing?.

 

[bananasiong]

if it is not simple.. then i will try the simplest way.. by adding more batteries..

what am i doing?? u mean what do i use with the stepper motor?

i use the stepper motor as the front wheel (direction control) of my lawn mower.

 

[Nigel Goodwin]

if it is not simple.. then i will try the simplest way.. by adding more batteries..

what am i doing?? u mean what do i use with the stepper motor?

i use the stepper motor as the front wheel (direction control) of my lawn mower.

If you don't mind me saying so, a stepper seems a VERY bad choice, a servo will give FAR more power, and also provide absolute positioning.

 

[bananasiong]

If you don't mind me saying so, a stepper seems a VERY bad choice, a servo will give FAR more power, and also provide absolute positioning.

oh.. but i've been doing this for months.. it is impossible for me to change the motor.. besides that, i really don't know how a servo works.. i know PWM only.. but how it works with PWM?? can u teach me?

 

[motion]

it is impossible for me to change the motor

I am afraid that's probably what you need to do.

I can imagine you're using one of those tiny airpax motors with a poor resolution of 15 degrees per step, clearly not enough for use in steering. You need a reduction gear to get a higher torque and finer resolution.

Also, the motor's voltage rating is higher than your power source and so you can't even get the rated torque. And so, you now have to make a fancy motor driver that is clearly out of your league.

Rather than struggle with a failed choice, you also ought to consider changing the motor.

 

[Papabravo]

It is a sad commentary on the profession we've chosen that sometimes we must be prepared to throw the first one away, because we usually end up doing that anyway.

If you do end up starting over you will have our condolences and our support. I know how hard this must be, but please don't dismiss this advice out of hand. If you do start over, you must first define your requirements. The reason for this is so you and everyone else will know what "done" means.

Good Luck

 

[bananasiong]

okay.. thanks for all your advises.. but the first thing i have to do is, settle what can i do first. i will try to increase the voltage supplied first. but i've tried that before, i'm not sure about the torque, one thing i know is, if i increase the voltage, around 12V, the motor becomes heat.

 

[Nigel Goodwin]

okay.. thanks for all your advises.. but the first thing i have to do is, settle what can i do first. i will try to increase the voltage supplied first. but i've tried that before, i'm not sure about the torque, one thing i know is, if i increase the voltage, around 12V, the motor becomes heat.

Stepper motors DO run hot, if it's a 12V motor you want to run it off 48V or so, with large wirewound resistors to limit the current - or use PWM to limit the current (but resistors are likely to be simpler for you!).

This will give best torque out of the motor, but I suspect it won't be anywhere near enough? - how big is the vehicle you're trying to steer with it?, and do you have the motor geared down?.

 

[bananasiong]

it is around 30*35 cm and i think less than 5 kg
i use the stepper motor as the direction control, it turns just around 60 degree when needed.
and there is no gear. straight away connect it to a caster wheel.

 

[Nigel Goodwin]

it is around 30*35 cm and i think less than 5 kg
i use the stepper motor as the direction control, it turns just around 60 degree when needed.
and there is no gear. straight away connect it to a caster wheel.

I think you're probably asking a LOT from a stepper!, an RC servo is made to do this job, and is extremely easy to drive, requiring a 5V (PIC compatible) pulse every 20mS.

 

[bananasiong]

I think you're probably asking a LOT from a stepper!, an RC servo is made to do this job, and is extremely easy to drive, requiring a 5V (PIC compatible) pulse every 20mS.

oh.. can the servo turn in accurate degree? but i'm not using the PIC. i'm using the motorola 68HC11 microcontroller. and what about the PWM? is it pulse width modulation? i don't know what about that..

 

[Nigel Goodwin]

I think you're probably asking a LOT from a stepper!, an RC servo is made to do this job, and is extremely easy to drive, requiring a 5V (PIC compatible) pulse every 20mS.

oh.. can the servo turn in accurate degree? but i'm not using the PIC. i'm using the motorola 68HC11 microcontroller. and what about the PWM? is it pulse width modulation? i don't know what about that..

The servo can turn accurately, and it provides absolute positioning, which a stepper doesn't - it's not really PWM, simply a positive going pulse between 0.5mS and 1.5mS repeated every 20mS or so (although the 20mS isn't at all critical). The position of the servo corresponds to the width of the pulse, with 1mS being it's centre position.

 

[bananasiong]

wah.. does it take a long time to learn this?
how if reverse?
if i want to learn this, first of all i have to get a servo motor.. i think it is expensive right?

 

[Nigel Goodwin]

wah.. does it take a long time to learn this?
how if reverse?

You don't 'reverse' it, it gives absolute positioning, you simply provide it a pulse and it moves to the position that pulse width represents.

if i want to learn this, first of all i have to get a servo motor.. i think it is expensive right?

No, quite cheap, in the UK probably from around £10 upwards? - you can get them from electronics stores or model shops.

 

[bananasiong]

You don't 'reverse' it, it gives absolute positioning, you simply provide it a pulse and it moves to the position that pulse width represents.

it cannot reverse?
i need it to turn both direction like what a stepper can do.

my front wheel is a direction controller, it has to turn either 60 degree to the left or to the right. can a servo do this?

 

[bryan1]

it cannot reverse?
i need it to turn both direction like what a stepper can do.

my front wheel is a direction controller, it has to turn either 60 degree to the left or to the right. can a servo do this?

Does rain fall up or down :?: If you bother to look at a servo AND READUP on some infomation and READ the other posts in this thread you will find your answer. If it isn't spelt out in plain english read again and again and if you still don't understand how a servo works try playing with lego. Enough said :!:

 

[Nigel Goodwin]

You don't 'reverse' it, it gives absolute positioning, you simply provide it a pulse and it moves to the position that pulse width represents.

it cannot reverse?
i need it to turn both direction like what a stepper can do.

A servo doesn't 'rotate' at all, it just turns within a limited range, probably between 60-90 degrees - this can easily be mechanically linked to do steering, and is what they are designed for - all 'proper' radio control models use them.

You're still thinking steppers, where you move so many steps left, or so many steps right (which is RELATIVE positioning, and pretty useless for steering). With a servo you just tell it WHERE to go to (by the width of the pulse), such as 10 degrees left of centre - you don't need to know where it WAS (as you would with a stepper) - you just tell where you want it to go (this is ABSOLUTE positioning).

my front wheel is a direction controller, it has to turn either 60 degree to the left or to the right. can a servo do this?

A servo itself won't turn 120 degrees, but a mechanical linkage can increase it - check 'proper' radio control model cars, you will easily see how they work.

 

[bananasiong]

Does rain fall up or down :?: If you bother to look at a servo AND READUP on some infomation and READ the other posts in this thread you will find your answer. If it isn't spelt out in plain english read again and again and if you still don't understand how a servo works try playing with lego. Enough said :!:

if u feel don't like to explain, just keep quite and don't interrupt others' discussion. those expert will give me the right answer.

A servo doesn't 'rotate' at all, it just turns within a limited range, probably between 60-90 degrees - this can easily be mechanically linked to do steering, and is what they are designed for - all 'proper' radio control models use them.

You're still thinking steppers, where you move so many steps left, or so many steps right (which is RELATIVE positioning, and pretty useless for steering). With a servo you just tell it WHERE to go to (by the width of the pulse), such as 10 degrees left of centre - you don't need to know where it WAS (as you would with a stepper) - you just tell where you want it to go (this is ABSOLUTE positioning).

thanks for your info, Nigel :wink:
is the torque high enough if i use only 5V to drive the servo? i there many model?