Hi Everyone,
I'm new in this forum so a big Hello!
I'm planning to do a poject in which an object is placed on a turntable and this table hast to be controlled remotely to change its rotation.
The object will be pretty heavy, round about 10kg plus a plate where it placed on, so lets say 15kg.
Size of the plate will be round about 50x50cm.
When I was a student, I did a project with a stepper which I controlled directly out of a Java programm conected to my parallel port.
I figured out that it is not so easy to find the correct frequency in which the stepper wants its data.
So I'm wondering, is the implentation inside of the arduino board so good that the stepper always does as much steps as I want him to do?
Or do I need a second device giving me the relative position or sth like that?
What stepper could handle that weight? Or do I have to use a servo?
Depending on your budget, you could also look into a brushless servo - most currently available ones have a step direction interface which simplifies the control interface. From 30watts to kilowatts, just depends on the price...
If you size your drive (motor and electronics) properly your should have little problem with the turntable being where it should be. If you undersize your drive then you will have problems. There are several hobby CNC systems (Mach3 for one...) that use the steppers and give excellent results. I have used servos in stepper mode in industrial applications and never had a problem.
You need to figure the torque you require to accelerate and slow down as well as teh torque required to maintain motion. REMEMBER - gearing affects torque. If you are driving the turntable slower than the motor the torque goes up by the ratio of motor speed to turntable speed. Size your motor higher than the max torque required and you should have no problem.
I suggest finding an old microwave and taking it apart to find the turntable motor. It should already have a gear drive in it and would be simple to hook up. I think they are 12 volts DC. That would free up your budget.
I find them in back alleys all the time. The really old ones have a huge transformer in them.
2 phase pancake style syncronous motors work well as soft steppers, since they are constant speed ac motors the don't have agressive detent torque like a stepper. The stepper having an enhanced detent torque so that position is held when not stepping. Seeing as you want to rotate something with a high inertia, the syncronous motor approach would be the better suit. You drive it just like any other 2 pole bipolar stepper 2 square waves 90degrees apart via an h bridge driver such as the Motor3 shield.
It helps tremendously if you tell us what your application actually is.
For example is this load you want to rotate a lump of meat to roast or an object you want to scan a 3D points cloud? Both have diffrent solutions.
I figured out that it is not so easy to find the correct frequency in which the stepper wants its data.
No it is very easy to work this out.
don't have agressive detent torque like a stepper.
Calculating step rate is not a real problem. How fast do you want your final speed to be? What is your gear ratio? You know the number of steps to rotate the motor 1 time. (common ones are 200 steps per revolution) if you step the motor 200 times per minute you will get 1 RPM. If you have a 5:1 gear reduction you would have to step the motor 1000 times per minute to get 1 RPM at your turn table. If you want 2 rpm you double the steps per minute.