Notifications
Clear all

stepper vs servo  

  RSS

lobster
(@lobster)
New Member
Joined: 8 months ago
Posts: 2
2020-03-20 8:04 pm  
For an actual project I have some specific questions.
 
The aim is to control a motor with a joystick. This sounds easy in the first place but it isn't
as the control should be as follows:
having a 1 achsis joystick the motor should follow the joystick proportionally and linear as it does in rc plains and cars.
In other words, if the stick is moved half to the left side the motor should turn half the way to the left side too and with a full movement to the right the motor should turn full to the right, leaving the stick alone = neutral position the motor retuns to his neutral = middle position too.
Ofcourse the max endpoints of the motor and the stick must be equivalant or adjusted like that.
 
Now I know that this behaviour is already possible in rc models with servos and a remote
BUT
I would need a lot more torque that only a stepper can fullfill I believe.
 
Is there a way to bring the stepper to the same behaviour (see above) as a servo ?
 
All videos I saw showed the stepper moving left or right, slow or fast, only as long as the stick was pushed to the side. Not practical at all
for this project.
 
Now, while I was waiting for the invitation to this forum I did more research and the 'closed loop stepper'
or 'hybrid stepper', this could be it I believe - do you agree?
Even if it is, it's getting more complicated as the steppers shaft movement from -45° to +45° should happen within 1 sec or less. As I heard that stepper lose torque the faster they turn - right?
 
Thanks for reading and maybe answering 🙂
 
andy

Quote
JBeazy
(@jbeazy)
Eminent Member
Joined: 1 year ago
Posts: 23
2020-03-21 6:04 pm  

What is the motor driving?  Is it linkages , pulley and timing belt, or other?

It seems you want the position of something to be determined by the position of the joystick. And you say a servo motor could do it but you are concerned about the torque. And with stepper you are not sure about the speed?

So I think to start we need to know some specifications:  what you are driving with the motor, how far (angle) are the two extreme positions, how much time (secs) to get from one extreme to the other, and what is maximum torque expected?  Note if you are trying to move a mass from one position to another relatively fast the motor must provide that extra torque but that can be accounted for if we know what is expected of this system.


ReplyQuote
lobster
(@lobster)
New Member
Joined: 8 months ago
Posts: 2
2020-03-22 2:04 am  

Ok, ok I see, more detail is needed, so here is the whole story:

I'm sitting in a wheelchair - for the moment I'm driving a power wheelchair controlled by a joystick - but ordered a seated segway and will get it next week but I want to be prepared.

My goal is to replace the steering, which is normally done by the handle bar pushed left or right, by a motor.

In seated segways the handle bar can be removed for better access.

This reduces my questions to one simple task.

I would add a drawing but don't know how. So I try to describe it as good as possible.

The result should be to turn the shaft of the segway around its pivot point. So I need either a lever of a certain length or a belt driven disk of a certain radius. Both are the main key element in the force needed. This force  acts perpenticular to the radius or the end of the lever.

Assuming the neutral position of the shaft equals 0° and is identical with the zero point / home position of the motor I will need to turn it around its pivot to -45° and +45° maybe its -50° and +50°. If these are the both extremes they must be reached with 1 sec or less. So the angle span of lets say 100° in 1 sec is the speed that is required. The longer the lever or the radius the less force is required, but I'm limited in space.

I was searching several segway pages to get an info about how much torque is required to turn the shaft but no success. If anyone knows please let me know.

Also, if at all possible, a way to attach drawings.

 

Thanks

andy

 


ReplyQuote