Mechanical Advantage And Force

idbruce

To Those That May Be Interested

In another thread, I recently and briefly discussed a screw driven guillotine music wire cutter, and as mentioned in that thread, this was a third generation design. However it is noteworthy to mention that two of the designs were capable of cutting the wire, but the second design did not fulfill my vision of the machine as I could foresee it. During the construction of this cutter, as well as with other mechanical devices I have built, I had come to the conclusion that I needed more force than my motors could deliver. When building machinery or other items such as robots, there will be times when you just need more force than your motors, servos, or other power output devices can deliver. There are several ways to get more force out of a power output device, but it requires a gain of mechanical advantage.

Wikipedia defines mechanical advantage as follows:

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever.

http://en.wikipedia.org/wiki/Mechanical_advantage

During my adventures of machine building and other projects, I have used several means as a way of gaining a mechanical advantage or force, some of which are as follows:

• Levers
• Gears
• Wedges
• Screws
• Sprockets
• Pulleys

In my experience, to obtain a greater mechanical advantage, I have always had to sacrifice speed, but this was always much more appealing than a huge power output device. If you have a project where you simply need more force, then do a little research into the area of mechanical advantages. There are many ways to gain a mechanical advantage and incorporate it into your design, you just have to use a little imagination.

Bruce

LoopyByteloose

Mechanical advantage is everything. I used to lift houses and put a new foundation under them. One can take a nice old one-story house and lift it up 10 feet in the air and build a garage and added living space under the existing house if you know what you are doing. And of course, you can also lift and move houses across town if you get one for free. It is easy to rent all the gear.

The biggest lift I was involved in was 400 tons. At the time, it was the largest in North America. But these days, that is rather small.

Wedges end up being handy in the oddest of places. I have built a lot of temporary wood clamps that held work together while glue set with wedges rather than buy expensive clamps. And often, a wedge can open up a crack enough to insert a pry bar to lift something that seemed impossible to grasp.

Tripods of 2" water pipe can allow you to lift quite a bit with block and tackle.

idbruce

Loopy

I was going to quote Archimedes, but there is definitely some discrepancies in what he actually said between 287 and 212 B.C, so I will give you a couple of choices:

1. Give me a long enough lever and a place to stand, and I will move the earth.

2. Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.

3. Give me a place to stand and with a lever I will move the whole world.

I suppose I will have to fire up the old Parallax powered time machine, just to find out what was actually said.

Bruce

Irone

You can also increase force by lowering the load required. I am a die maker and at work we had a prestamped part that was cut into 8 sections with 7 punches at the same time. The first thing I did was see if the engineer put a large enough pneumatic cylinder on to do the job. He put one on that just barely had enough power to cut the material but did not add more for sliding the steel punch holder. If we put a larger cylinder ( I wanted one twice as big ) the whole fixture would have to be redesigned. I checked the length of the punches and found out I could grind half of the thickness of the material from the working end of the second, fourth and sixth punches and still have enough length to push the chips deep enough in the die. The material breaks when the punch is half way thru so we cut twice with one motion.