DIY Stringing Machine : Ariadne Mitos II

Issle

New User
Hi.

Today I finished my second personal stringing machine as a DIY project. It's an automatic dropweight that combines the Wilson diablo drum and the Stringway automatic dropweight system, so I wanted to share my enthusiasm with the public. Feel free to ask any questions.


 

Irvin

Talk Tennis Guru
I love it! I really like to see anyone being creative and coming up with ideas on there own. But a Diablo on an automatic drop weight? I can’t see how that works. Can you post a picture of the Diablo / ADW? Seems like a Gamma String Roller would be a better combination. What is the function of the Diablo with this combo?
 

Issle

New User
The diablo drum is used reduce the force of the string that reaches the gripper that's on the opposite side. I wasnt able to make a gripper like the one they have on the Stringway ML100. Mechanicly its the most difficult part to make. My gripper has just a spring that pushes two diamon dust plates together (the force is not generated by the dropweight) so I had to reduce the tension that reaches the gripper because the string would slip.

Ever since I saw the automatic dropweight system I fell so in love with it, but I consider the prices of the Stringway machines too much for my pocket. So having it on mine was a big must :p

Tomorrow I'll string my racquet and film it since I just completed the machine. I've been working on it with my father nonstop for 9 days in his lab.

 

Issle

New User
Some more details I didnt post earlier.

The rotating parts (base of frame mount and dropweight base) are made out of used car parts, specifically the ball bearings of car wheels. There's two of them each of them cost 20 euro used from wreckage shop.
The weight is 2.5kg of gym equipment that cost 6 euro.
The rest of the metal is plain cheap hardened steel or iron that costed about 20 euro.
The table is a modified IKEA furniture that was like 15 euro.
The black pain is 3 euro gloss spray.
The gray paint is hammer paint that cost about 5 euro.
The other parts (screws etc) were another 20 euro.

For the construction the specialized machinery used was welder, metal grinder and a mill.

The most difficult part was taking out the ball bearings from the car wheels. They are screwed in so extremelly tight to withstand the forces of a moving car.
Also getting the angle of the automatic dropweight right was tough too, needed simulations in CAD software to figure out the right angle that would provide constant stable tension over a range of tensioner angle. Turns out that it's not 90 degrees as the guys at Stringway claim but a little bit smaller.
Generally as a project it's not very difficult. It needs a lot of patience and time because it consists of many small parts that need fine grinding to get them to fit properly.
 
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elkwood

Hall of Fame
wow nice bit of engineering !!! Only issue i see off the top of my head is the angle of the string from the rac to your diablo. The
pic makes it like really steep. I think its awesome u built something yourself !!! Hope it works !!!!!
 

Issle

New User
The vertical angle of the string entering the frame is 5.87 degrees. It was the minimum I could use in order for the racquet frame handle to be able to pass above the tensioner. To counter for the tension loss, we decreased the angle between the tension bar and the drum from 90 by 5.87. We run simulations at sketchpad and decided to use that angle. This angle for nylon and plastics with an average of 0.2 static friction coefficient makes the machine lose about 0.2 * sin ( 5.87 ) tension percentage which is about 250grams tension loss at 20 kg. Not so much loss.


As for diablo drum tension "regulation" the static friction between the drum and the string absorb part of the tension, so the tension that reaches the gripper is smaller so the string wont slip from inside the diamond dust plates that are compressed by a simple spring.
 
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Ultra 2

Semi-Pro
Wow, this is too much for me to absorb.. that's why dummies like me resort to buying a stringer.. lol. Great work!
 

Irvin

Talk Tennis Guru
The vertical angle of the string entering the frame is 5.87 degrees. It was the minimum I could use in order for the racquet frame handle to be able to pass above the tensioner. To counter for the tension loss, we decreased the angle between the tension bar and the drum from 90 by 5.87. We run simulations at sketchpad and decided to use that angle. This angle for nylon and plastics with an average of 0.2 static friction coefficient makes the machine lose about 0.2 * sin ( 5.87 ) tension percentage which is about 250grams tension loss at 20 kg. Not so much loss.


As for diablo drum tension "regulation" the static friction between the drum and the string absorb part of the tension, so the tension that reaches the gripper is smaller so the string wont slip from inside the diamond dust plates that are compressed by a simple spring.
Very nice and you’re right the makeshift Diablo will reduce tension a great deal but your diablo is what is actually applying the tension, and if your weight arm is not at the same position every time you tension the string the radius from the center of the pivot to the outside edge of the Diablo is not the same. Your torque applied by the arm is close but because the radius changes the leverage changes. Any drop or increase in leverage changes you tension.

So you go around the diablo shaft a few times then to some diamond dusted gripper plates. Does this mean you must release the string if you weight arm isn’t level?

I still like your ideas.
 

Issle

New User
You are right. The diablo drum indeed changes the leverage a bit depending on the angle. For angles around +- 20 degrees the tension difference is about 150 gr. It's a compromise sadly that had to be done. The thinner the diablo drum, the less this loss. But if we made the diablo drum very thin (aka small diameter) then it would damage the string that goes around it as it would have to bend a lot. The optimal way (using plates that compress as the tension bar drops) is a bit complex to make so we avoided going at that length.

Personally I'm very satisfied. I'm not a professional stringer so I'm not in need of a very fast electronic machine. But as a competitive player, getting to play with fresh strings every couple of hours is a blast. First world problems, what can I say :p.
 
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Issle

New User
Oh funny side story. The first time we made our poles that fit the racquet, we didnt know that as you progress from R1 to R8 mains the tension on the frame and the poles supporting it accumulates. We used metalic water pipes cause we thought it would strain at max 30 kg. Once experimenting at around R6 on both sides, the machine broke down together with the racquet that was mounted. :p Hard learnt lesson hehe.
 
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