- #1

pete

- 72

- 5

https://www.ondrives.com/sr119

They come in many sizes and I've been trying to get my head around the specifications so I buy the right one.

Take the one I linked above as an example, it's listed as 6.18N (63kg) at the top of the page and further down under the specifications tab it lists it as having 63 Kg cms or 6.18 N Torque along with the dimensions of the drum the spring would wind onto.

Considering the size of the spring, this seemed to me like a very small number in N and a very large one in Kg. My maths is not too good. Neither is my physics but I spent some time looking up how this works and what the equations are so I can try and resolve what weight this spring would counterbalance.

This is the bit I’m hoping someone can look at and tell me if I’m doing this right. I tried posting this in the Engineering forum but no one answered so I thought I'd try my luck over here. I'm not looking for someone to do the work for me, I just need someone to look at it and see if I'm going in the right direction before I commit to buying things.

I took the diameter of the Torque output drum: Diameter [D3] in the specifications list, and divided it to get a Radius of 87mm, so 8.7cm. Then I changed it to meters, so .087m. Then I divided the Torque, 6.18 N by this to get roughly 71 N force. So a barrel of the same diameter as D3 with a cable wound around it will give me about 7Kg counterbalance over the extension of the spring, 12.8 meters. This still seems low to me but then I have calculated for a barrel with a 17cm diameter. Once you get down to an output shaft of around 15-20mm it would be around the 63kg point.

How did I do? Am I reading the specifications right, do I have the right equation or anything else you notice?