Double torsion spring vs. two torsion springs (left and right hand)
Double torsion spring vs. two torsion springs (left and right hand)
(OP)
I am designing a mechanism with a torsion spring on each side of a base that work together to hold an arm down. Each spring is warped around a 0.7" boss. The arm is 17" long. I am trying to get 10-lbs of force at the tip of the arm when it is opened out 135 degrees. I have attached a sketch of the set-up.
I was thinking of using two torsion springs (a left and right hand) and each spring would be 4mm wire diameter with 5 coils.
Will this give me the appropriate force of 10-lbs at the top of the arm?
If I used two springs instead of a double torsion spring will it act the same?
How does having 2 springs effect the force? Do the forces from each spring add together?
Are there enough coils?
I was thinking of using two torsion springs (a left and right hand) and each spring would be 4mm wire diameter with 5 coils.
Will this give me the appropriate force of 10-lbs at the top of the arm?
If I used two springs instead of a double torsion spring will it act the same?
How does having 2 springs effect the force? Do the forces from each spring add together?
Are there enough coils?





RE: Double torsion spring vs. two torsion springs (left and right hand)
http://www.centuryspring.com/
Alternatively, here a link to an online calculator.
http://www.engineersedge.com/spring_torsion_calc.htm
-Dustin
Professional Engineer
Pretty good with SolidWorks
RE: Double torsion spring vs. two torsion springs (left and right hand)
The double torsion spring will act similarly to 2 single torsion springs, and yes the forces should simply add. Double torsion springs can be easier to mount/install/assemble etc. than 2 separate springs. It will of course depend on your application but I strongly suggest looking at the double torsion spring.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Double torsion spring vs. two torsion springs (left and right hand)
Where is the sketch?
RE: Double torsion spring vs. two torsion springs (left and right hand)
RE: Double torsion spring vs. two torsion springs (left and right hand)
It looks like the sketch didn't attach the first time, I am attempting to reattach it.
RE: Double torsion spring vs. two torsion springs (left and right hand)
http://www.c-flex.com/stiffnessproperties.html
RE: Double torsion spring vs. two torsion springs (left and right hand)
How C-Flex can do 135 degrees?
RE: Double torsion spring vs. two torsion springs (left and right hand)
RE: Double torsion spring vs. two torsion springs (left and right hand)
RE: Double torsion spring vs. two torsion springs (left and right hand)
tables in Machinery's Handbook as follows
For a working stress of 140,000 psi with an ID=0.8125", you need a wire size of 0.2437 inches with a deflection per coil of 8.346 degrees and an allowed torque of 199 lb-in (determined by the wire diameter); you need 170 lb-in)
So you need a total of about
150/8.346= 18 coils
or 9 coils on either side
assuming 15 degrees preload.
You can reduce the torque to 170 by increasing the number of coils or increasing the ID of the spring ; for the former, I get
199/170*18=21 coils ; the stress would also decrease in the same proportion.
A useful design formula
ND= E*d^4 *defl/(4000*T)
allows you to manipulate N and D to get the best configuration.
N= active coils
d= wire dia
E= modulus of elasticity
T torsion required
D mean spring diameter =ID+d
defl total deflection including preload
Now you can go to your friendly spring coil vendor with some idea of what you need.
RE: Double torsion spring vs. two torsion springs (left and right hand)
Regards,
Cockroach