# Establish a controlled rotation on gears

I am a 3d designer trying to build a simple device for my project and I have a problem. As you can see in schema below, point G has weight on it and it needs to be a controlled, vertical rotation. I am afraid that when I build this, it will go faster or slower on sides. Rotation needs to be stable and I need rotation to stop where it is, as soon as motor stops.

• Can a mini motor achieve this and what kind?
• Do I need to add extra parts to the device and what are they?

• 3D designer seems a bit ambigious to me. Is that a 3D artist or industrial designer? – joojaa Jul 25 '18 at 9:39
• Well, actually a software engineer but the project I am working on demanded so many 3d models and prints that I don't know what I am now :D – user2344448 Jul 25 '18 at 10:38
• Do you mean by 'controlled, vertical rotation' that the part in your diagram is rotating in the vertical plane, and therefore the motor must raise/lower the mass G? – welf Jul 27 '18 at 0:25
• When you talk about 'go faster or slower on sides' are are you wanting to control the speed in a certain direction (e.g. vertical speed)? Most motors will rotate at a fixed speed when driven by a fixed voltage (and with a constant load), which will provide a sinusoidal speed if considered in only one axis. To change this you would need to control things either electrically, or mechanically, or both. – welf Jul 27 '18 at 0:31
• @welf By controlled, I mean stable speed. Basically rotation like arms of a clock. It is on planning stage and because I have no knowledge of motors, I was scared that with the weight on the tip of arm, it would do an uncotrolled rotation because of gravity. As suggested by joojaa, stepper motors resists certain amount of force that is not produced by motor so you will have a stable rotation. – user2344448 Jul 28 '18 at 9:03