Yoyo string making motor sled

Intro

So, I <3 yoys. I am an intermediate player [by the actual yoyo community standards] and a master [by non-thrower's standards (lol)]. In other words, I know my way around a yoyo, and I know yoyo string. I also make yoyo strings. Been making them for almost 3 years - about as long as I've been "throwing" [play with my yoyos]. 

• Fun Fact: polyester yoyo strings wear out after about 30 min to an hour of solid play.  

After extensive testing and tweaking, I have developed multiple recipes that I'm happy with, as well as a string making rig that has been dialed in to my main go-to recipe.

My rig currently allows for 6 strings to be laid out at a time, but have to be spun individually with a dremel. This is not my rig, but I'd like to make a motor sled resembling this one, but I want it to be more fine tunable:

Here, it looks like he is operating the motors with a simple on/off button. I want a more detailed control panel. 

The catch: "reduction"

Before I get into the specific functionalities I'm looking to achieve with this rig, I need to explain what "reduction" is, and why I need to design this motor sled to have these functionalities.

String making 101

Example recipe:

base length: 110"

reduce: 10% → 99"

10% of 110 = 11

110 - 11 = 99

finish length: ~50"

Using this example recipe:

The process is actually relatively simple. It starts with wrapping a desired number of threads around 2 anchor points @ 110" apart. 

• Fun Fact: the more wraps of thread, the thicker the finished string will be. Also, the longer the distance is between your two anchors, the longer the finished string will be. 

Next, hook the strands at the second anchor point with a hook loaded into the chuck of a drill of some sort, and lift the strands off of the anchor.

From this point until the string is finished, there needs to be a steady tension on the string. This is very important. 

Spin clockwise. Here's where the magic starts. As the threads spin together into one string, they get tighter and tighter until eventually they begin to reduce in length. The string will "pull" the drill toward the 1st anchor point. For this example recipe, stop the drill when the string reaches 99" from the first anchor point.

• Fun Fact: less reduction will yield a looser wound [and thicker] finished string; more reduction will yield a tighter wound [and thinner] finished string. Once the desired reduction length is discovered, it can be turned into a % (reduced length is what % of base length?). The cool thing about % based recipes, is that you can achieve the exact same reduction no matter how long the base length of the run is - which will yield a consistent string no matter how long it is.

Next, double the string in half, keeping a steady tension on it. Hook the string with the drill at the folded end and run it in reverse until its torsion has been adequately relieved. 

That's pretty much all there is to it!

The tricky thing about accurate reduction, is that the tension is a factor that often gets overlooked. It isn't a problem for the typical DIYer, but I want consistency and volume - call me a perfectionist. I'm looking to hone my "reduction / tension" relationship. 

A string that has just been reduced is pretty stretchy. And without the use of a spring scale of some sort, it is very difficult to accurately gauge reduction by feel.

This is what I need to factor into this motorized rig. The video I shared above is a good start, but I want to take it farther. 

The sled concept

This is hopefully where you guys come in. Here's what I would like the components to be capable of:

The motors:

• 15,000 rpm +/-
• stops quickly, doesn't have a "slow down" period after being shut off
• forward/ reverse option would be a plus, but not necessary 
• cheap (I'm on a budget)

Controls 

• straightforward "on/off" switch [or button] AND,
• programmable run time presets (push a button and the motors run for a preset amount of time, set by me)
• easily fine tune time presets (at least down to half a second, finer would be a plus)

Special needs 

• motor axles need a hook of some kind (maybe a coupling + hook)?
• whether internally or externally - motors need to be able to resist relieving the string torsion when shut off after reduction 
• all motors (6 minimum) must spin at the same velocity and time 

And again, all of this will be assembled in a similar fashion to the one seen in the video above. Control panel can be attached somewhere on the motor sled, could be a remote - whatever works.

Final thoughts

So, my goal after sourcing the appropriate components and assembling the sled, is to make a single string at a time with just one of the motors operated with the simple on/off switch. I will use a timer to time the reduction, and check with a spring scale until I get the time/reduction/tension just right. Then [hopefully] program the timer and do some more test runs with all of the motors to make sure everything is dialed in correctly. 

Sory to post such a lengthy topic! I just have a very specific concept in mind, that just so happens to be very simple at the same time. Like I said, I know what I need the components to do, but I don't know much about electronics. 

Any thoughts?