On 23 February 2015 at 08:54, Viesturs Lācis <viesturs.la...@gmail.com>
wrote:

> I would appreciate, if someone could share a source for torsion
> springs, moment needed is 70 Nm, when there is 90 degrees still left
> to reach max angle (for 270 degree max angle that would be ~105 Nm max
> moment).
>

Lets take the example of a straight torsion bar and see where we end up.

Springs typically go to about 80% of UTS, so lets guess at 1GPa.

The stress on the outside of a solid shaft in torsion is...
http://www.engineeringtoolbox.com/torsion-shafts-d_947.html

Torque_max = (pi  / 16) stress_max * D^3 so you would need a solid shaft of
7mm dia.

So it sounds possible.

But you need 70Nm at 90 degrees rotation and safe stress at 270.

Angular deflection theta of a shaft (radians) = 32 L T / (G pi D^4).

G for steel is 75GPa. You want to solve for L and D at
T = 70Nm and theta = pi/2
T < Tmax and theta = 3pi/2

Which, is, err, left as an exercise :-)


-- 
atp
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