I have a very basic physics question but I’m not confident I know the answer. I need to use a servo to rotate a cylinder on its radial axis, but there’s going to be some mass on one side of the cylinder (about 0.5 kg). I could easily use a round servo horn, but I started thinking that a long servo horn might provide more torque to move the heavy side of the cylinder. However, the servo itself only provides a certain amount of torque, and as long as the whole cylinder is moving together, does it make a difference?
I have a very basic physics question but I’m not confident I know the answer. I need to use a servo to rotate a cylinder on its radial axis, but there’s going to be some mass on one side of the cylinder (about 0.5 kg). I could easily use a round servo horn, but I started thinking that a long servo horn might provide more torque to move the heavy side of the cylinder. However, the servo itself only provides a certain amount of torque, and as long as the whole cylinder is moving together, does it make a difference?
I’ve attached a picture for clarity.
Actually the picture, without labels, just makes less clarity.
The applied torque of the servo is REDUCED by using a longer arm. How far from the cylinder you attach the end of the arm also affects the torque need to move the cylinder. Unless the cylinder is horizontal, so gravity is pulling the cylinder, but you failed to discuss the orientation of the weighted cylinder.
A nice drawing of your device, showing the weighted side and the orientation in relation to the floor would provide clarity.
Sorry about that, it seems so clear in my head, but it's not always easy to know which pieces are obvious and which are not.
I'm not sure if me drawing something would make it more clear or less clear, so I'm adding a picture with the servo mounted. I will add a video as soon as I figure out how to convert .MOV files to something I can post here. As you can see, the rotation of the cylinder is exactly in line with the rotation of the servo, and I'm wondering if different servo horns affect the amount of force that can be transferred from the servo to the green cylinder.
My thought is that it makes no difference which servo horn I use, as long as the connection between the servo and the green cylinder is good. But I'm going to attach other stuff to the green cylinder, and I have this idea tugging at the back of my head that the servo would generate more angular momentum if I had a longer arm extending towards the outer part of the green cylinder.
Incidentally, I know you can see the 4 armed servo in my very first picture, but that is there because of a stupid design decision that I didn't see until I put it all together. Now, to take the horn out, I'm going to have to cut it into two pieces. I really need a servo horn that I can add AFTER the cylinder is in place, so my thoughts are to go with a small round one and attach it to the cylinder with long screws, or just use a longer horn.
And that got me thinking about which one would transfer force better.
Available torque is not affected by the length of the arm at all. Its purely a property of the servo, which
outputs upto some limit value.
Lever arms convert torque to linear force, using the equation
force = torque / radius.
That's it.
If you are trying to generate a linear force from a torque all that matters is the radius distance
between the shaft and the line of action of the force. If that distance is constant and the horn
length varies, the horn length is completely immaterial. If that distance is the horn length
the the horn length matters completely.
If you are trying to twist something, torque is constant for the whole shaft.
Another way to consider torque (and in fact the best IMO) is to treat it as energy per unit angle.
Thus you can measure it in joules/radian. Linear force is joules/metre.
That answers my question exactly. I also appreciate everybody else that tried to help, and I'm sorry my question ended up being so unclear. Maybe my use of the term "cylinder" was inappropriate; the green part is the part that I'm rotating, which isn't truly a cylinder because it's got that extra stuff hanging off the side.
