Slot and Pin Mechanics - Moment Arms

[ptc-2151062]

Dear all,

this should be simple, yet somehow I seem to have forgotten my mechanics 101.

Referring to the attached image, I have a pin that runs in a slot. The pin is mounted onto a arm (highlighted in red) that rotates about T1. The part with the slot in it rotates about T2. So when the arm/pin starts rotating, the part with the slot turns about T2.

Assuming I know the torque input at T1 = 3.5 lb-in, then the resultant force F should be 3.5/1.25 = 2.8 lbs. No problems there.

Then, the resultant torque at T2, I think, is 2.8 * 0.4 = 1.12 lb-in.

Does that seem correct to you all? Where I am getting tripped up is in the interaction between the pin and the slot....I think I may be overly simplifying this.

I appreciate any input.

Andri

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[SylvainA. · Accepted solution]

It should actually look like that:

(sorry, I've made it with paint )

Force applied by Body1 on Body2 : F= T1/L1

The force between body1 and body2 (red arrow) is normal to the slot at point of contact between the pin and the slot.

Then, T2=F*L2

[ptc-2151062]

Sylvain,

that looks better. When I designed this part over a year ago, I had something like this, but drawn a little differently. The way you've drawn it makes it much clearer.

In my drawing, L1 was 1.05 and L2 was 0.269. In any case it is equivalent to yours.

Thanks for you help.

Andri

[ptc-2151062]

A sort of related question regarding mechanisms in Creo:

Lets hypothetically assume that the moment arm length L2 goes to 0 at some point in the mechanism travel (it doesn't for this design, but that was one of the concerns initially). Will Creo allow the mechanism to get 'stuck' when you drag components as it likely would in real life?

Andri

[SylvainA.]

Normally yes, it will.