How do you size a rotary damper?

 By Lisa Lin

Rotary dampers an support us when we want to find a soft-moving solution for the product. Typically, there are two situations.

  1. The cover lid can fall free because of gravity. However, the lid may plunge suddenly. We can install rotary dampers to make the top lid close softly.
  2. The cover lid can be opened because of the spring. However, the opening process may be too fast. We can also install rotary dampers to make the top lid open softly.

Now comes the question. After choosing the suitable model in the catalog how do we calculate the rotary damper torque?

You will know the answer by reading this article.

1. Soft closing

M: weight of the lid(kg)
L: length from pivot point to end of the lid(m)
T(torque): W\times 9.8\times L\div 2(Nm)

Example:
M=2kg, L=0.3m
T(torque)=2*9.8*0.3/2=2.94NM
Pls notice, the torque calculated by this formula is the maximum torque.

Damper soft closing

2. Soft opening

M: weight of the lid(kg)
L: length from pivot point to end of the lid(m)
T(spring): the spring force
T(load): the torque without the spring
T(torque): T(spring) – T(load)

Example:
M=1kg, L=0.2m, T(spring)=0.5~1.2Nm
T(load)=1*9.8*0.2/2=0.98Nm
T(torque)= (1.2 – 0.98)Nm ~ (0.5 – 0)Nm = 0.22~0.5Nm

Barrel damper for soft opening

3. Connected by gears

M: weight of the lid(kg)

L: length from pivot point to end of the lid(m)

Gear ratio=1：n (click to see what is gear ratio) 

T(torque): n*W*9.8*L/2(Nm)

Example: M=0.6kg, L=0.15m, gear ratio=1:1.5

T(torque)= 1.5*0.6*9.8*0.15/2=0.66Nm

Damper gear ratio

4. Two factors affecting torque

A. Temperature

The torque of the rotary damper varies according to the temperature.

The higher temperature for the lower torque.

The lower temperature for the higher torque.

When the temperature returns to normal, the damper characteristics will return to normal as well.

Temperature & torque

B. RPM

The torque of the rotary damper varies according to rpm.

In general, if the rpm goes up, the torque increases;

If the rpm goes down, the torque decreases.

In addition, please note that the starting torque slightly differs from the rated torque

(The torque value indicated in the product data is measured at the rotation speed of 20r/min)

RPM

Any doubt, we are happy to help.

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