You can select your diagonal rods whatever length you like, but:
The longer rods you select the lower your print area height will be.
- If you want to reach with your platform to the tower base (so that the corresponding diagonal rod is vertical) then you need your rods to be longer than sqrt(3) * deltaRadius. If you select the diagonal rod length just at this low boundary then you will be barely able to print behind the triangle defined by the towers.
- If you want your built area to cover a full circle with radius deltaRadius then you need your diagonal rod long at least 2 * deltaRadius.
The longer rods you select the lower your print area height will be.