You can actually go crazy with the design if you want to. L1/L2 needs to equal n/m where n and m are both positive integers. The ratio of the string wraps at AC vs BD will need to be m/n. This will guarantee a constant string length.
On a side note: you can see from the limit switch on the arms that I don't let them go past 140ish degrees. My test show that you get the constant force promised except for arm positions past 160-170 degrees. This lets me realize 90% of the theoretical range without getting into trouble.
On a side note: you can see from the limit switch on the arms that I don't let them go past 140ish degrees. My test show that you get the constant force promised except for arm positions past 160-170 degrees. This lets me realize 90% of the theoretical range without getting into trouble.