Go Down

Topic: Confused newbie question about servo vs. stepper for rotating an object 180° (Read 1 time) previous topic - next topic

rince

Hi,
I am just a beginner in the fantastic world of the arduino and also in anything electronics. I am planning a project which requires me to rotate a 3kg mass 180 degrees. Basically it is a rail with a weight fastened to it, which has to to rotate 180 degrees to the right and back. The whole process has to be smooth and must roughly take 2 seconds of continous motion and end in the same position it started.
There are DC motors which would be slow enough, but as far as I understand you can not stop the motor after 180 degrees and move back to 0 degrees. All servos I found were much to fast. So would the solution to my problem be to use a stepper ? Will a stepper handle this realtively high weight? Last but not least, how can I actually connect two steppers to an arduino?

Sorry for those beginner questions.

Kindest regards
Dennis

Robin2

A servo is very much easier to use so I suggest you try to make that work. It's probably also cheaper.

It is a common feature of Arduino code to make a servo move slowly by getting it to move (say) 1 degree at a time with a suitable interval between the movements.

If you don't already have a servo I suggest that you buy a cheap one and experiment.

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

rince

Thank you for your advice! I have a small servo from the starter kit, so I will try and see if I can make it work.
Thanks!

MarkT

Its not clear from your posting whether the 3kg mass is on-axis or off-axis - if its
off-axis you may need a large amount of torque to handle it, which will strongly
affect your choice of motion system.

Can you elaborate on the mechanical configuration?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

rince

Hi Mark,

thank you for your answer. So basically it is a bottle-like container which is strapped to a rail. The rail will then be connected to the
servo. So basically it is like an air propeller with some weight strapped to it.  The container which I want to invert will be filled with a liquid and has to stand upright. The axis of the servo will be in the middle of the container.

Thank you for all your help
Dennis

jremington

The output shafts of hobby-type servos can't support a significant amount of weight (a few grams, perhaps, but certainly not kg), so you will need a sturdy bearing to support the bottle and rail. Furthermore, attempting to rotate an unbalanced load will lead to a torque requirement that the servo may not meet. From your description, it seems that the load might be balanced if the bottle is full or empty, but do you imagine a situation in between?

rince

Thanks for the advice. I guess it really shows that I have not much clue on what I am doing. Yes, the bottle might never be completely filled. So yes, it is unbalanced. Obviously my idea of setting this up will not work.
How about mounting the rail to an axel and connect a belt drive to a servo. Would that have a better chance of working? That way the weight would not be on the shaft of the servo at least and with the right gears for the belt drive it might have more power, but then I guess I can no longer use a servo, as it may have to spin 360 for this to work.

Thanks
Dennis

jremington

It is very difficult to design an electromechanical device (and expect it to work) without some sort of preliminary analysis. Unless you already have a very sturdy motor-driven platform to work with , you will need to construct the mechanical part of the bottle/rail assembly first, then measure the torque required to rotate it under some realistic test conditions. Then you can decide what sort of motor and controller might work with the setup.

rince

Thanks. I guess I will do that then. Thank you for all your help. Would you know a good book I could read to learn more about motors and electromechanical devices?

Robin2

Keep in mind that you can get very powerful servos for not too much money.

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

Go Up