Motor selection for rotating table
Motor selection for rotating table
(OP)
Hi everybody,
I am building a rotational positioner for a robotic welding station. I am completely lost on how to tackle the driving problem - never dealt with motors aside from a class that I took 5 years ago (and failed it, the only failed class in my academic career).
I have 3 pivots, two of the loads (welding tables) are about 900 pounds, 36" wide and the main axis is 900x2 + 900, double the width. The tables will be rotated only 180 degrees, back and forth, a lot of start/stop action.
I started by approximating the load distribution at the ends of the table and finding rotational inertia, but not sure how to proceed..
Also, how realistic is it to find a motor to spin the table that would be less than 3.5"x3.5"? What other characteristics should I consider?
Thanks for any help!
I am building a rotational positioner for a robotic welding station. I am completely lost on how to tackle the driving problem - never dealt with motors aside from a class that I took 5 years ago (and failed it, the only failed class in my academic career).
I have 3 pivots, two of the loads (welding tables) are about 900 pounds, 36" wide and the main axis is 900x2 + 900, double the width. The tables will be rotated only 180 degrees, back and forth, a lot of start/stop action.
I started by approximating the load distribution at the ends of the table and finding rotational inertia, but not sure how to proceed..
Also, how realistic is it to find a motor to spin the table that would be less than 3.5"x3.5"? What other characteristics should I consider?
Thanks for any help!





RE: Motor selection for rotating table
What could be the velocity of each table and if the welding equipment would get some force [or better torque] as a constant load and for how much time.
RE: Motor selection for rotating table
A sketch speaks a 1000 words
desertfox
RE: Motor selection for rotating table
7another4, you got it almost right. The tables don't have the welding equipment, only the positioning clamps and the part to be welded. The two tables rotate independently of each other and the main frame.
I'm sorry, I don't have a picture before Monday, but this video - http://www.youtube.com/watch?v=UA5mTTEycbs - shows the concept.
RE: Motor selection for rotating table
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor selection for rotating table
I guess I'll call it a temporary (hopefully) mind block, if someone can help - please do!
RE: Motor selection for rotating table
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You may consider 180 degrees of rotation, back and forth and use air cylinders.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor selection for rotating table
If you want to go through the effort of building your own, there is significant engineering required. For a quick summary of the dynamics involved, websearch for "Smart Motion Cheat Sheet". Use that to determine your peak torque requirement which is a function of speeds, accels, decels, gravity effects, and rotational inertias. Your solution may involve transmitting the torque to your mandrel via gearing of different types. Size your motor for that. Depending on your accuracy & speeds required, you have a variety of options like AC gearmotors with encoder feedback, servo motors with encoders, or just dumb simple motors of some sort moving to a switch and/or hard stop.
For robotics, you also should take into consideration any mechanical deflections of your rig and stiffen it up structurally as required.
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Motor selection for rotating table
TygerDawg, we're building a very specialized machine, and hoping to make it simpler and cheaper than the head-tailstock positioners available. We need only 2 positions for both tables and the supporting frame, which greatly reduces the control complexity.
The plan is to use a DC motor with PWM control, proximity sensors for determining the end of rotation and locating pins for securing the table in position.
Does anyone know of a similar paper that would cover DC motor-specific design considerations?
Thank you again for your time and knowledge!
RE: Motor selection for rotating table
Second: Mass moment of input shaft must be multiplied by the ratio squared and added to the mass moment of the output shaft. The time to reach the rated velocity is about 0.03 sec but the table will continue to be rotated. So, what you need is the table velocity, let's say 30 rpm, and the time of rotating 180 degrees is about 1 sec. [1 rotation=60/30=2 sec, 1 half of rotation 1 sec.].
If the motor rated speed is 1800 you need a reduction of 1800/30= 60 [approximate].
The motor of 1/4 hp, as waross said, is suitable, of course.
The problem could be the number of starting per hour. I think the waross proposal of compressed air cylinder could be better.