Your drop weight machine is actually awesome (and accurate)

#Drop Weight Stringing machines ROCK#

As a stringer, I can understand wanting that super fancy, digital electronic tension stringing machine with the extra features and functionality like pre-stretch and knot mode and all of that. But maybe all of that isn't the upgrade you think it is! The humble drop weight is actually pretty awesome. Why? Physics!!

The magic of the drop weight is one of world's simplest and most useful machines - the lever. Levers are everywhere. Heck, your body is full of them. Fulcrum of them? Anyway. They allow us to move much larger masses than we'd be able to move with very little effort. The tradeoff comes with DISTANCE.


In this pic, you can see Arnie has to use a tremendous amount of strength to lift that rock, but Steve can do it with the lever. But he's got to move the lever a lot farther to move the rock just as much. This is exactly how a drop weight machine works.

Without the lever, we'd need machines that looked like this:


Wouldn't that be fun? Lifting and attaching 20+ kilos (50+lbs) to the string on every weave.

So instead, your machine uses the lever to accomplish this task with much less weight. My machine, a Tennisman 4000 (https://tennisman.de) uses a weight that is just shy of 3kg (6.6lbs). To oversimplify the equation of the lever, the force (f) exerted on the string by your drop weight lever is the distance between your fulcrum and the mass of the drop weight (R) X gravity. Since gravity is (hopefully) a fixed number, we can determine that in order to put 20kg of force on our string, we need the 3kg mass to be about 20 cm from the pulley. We gain a huge mechanical advantage


The amazing thing about this system is that for one thing - - It never needs to be calibrated (unless gravity changes and then we've got bigger problems) - It is VERY accurate. Because we're using fixed gravity and fixed weight, as long as we're pretty close to horizontal, your tension will be spot on. How close? 5 degrees high or low equates to 99.6% accuracy, 10 degrees? 98.5%. - It's constant pull. With a lockout machine, which seems to be a big choice instead of a drop weight, once the tension head is 'locked', it is no longer pulling. If the string is elastic, it will lose tension where the drop weight machine is always pulling. The bar may lower a bit but see above. - It's super zen. It's quiet, unpowered, and you can get into a flow that isn't much slower than using any other kind of machine - It's basically maintenance free.

A couple of tips on using your machine - Whatever you do, do not PUSH the bar down to get it to horizontal. If you look at the numbers above, adding a bit of extra pressure to the bar is massively amplified. Adding just 500g (1lb) of pressure to the end of the bar can add ~7kg (15lbs) of tension on the strings (wow!) - Grab a cheap little magnetic level and stick it on your weight to help you know when you're level. After practicing you won't really need it, but it is a huge help when starting out. - Different strings respond VERY differently. Multifilaments tend to be super stretchy, where polys are stiff and don't stretch much at all. You'll have to adjust your technique and starting points accordingly. For multis (all strings really), be careful to gently lower the weight down and don't drop it. Because of the elasticity, the racket can bounce back and forth, adding tension and stress you don't want.