Can I calculate or simulate how much force goes in to a movement? (models attached)

[et.teljemo]

Hi,

I'm working on a couple of ideas on how to force plastic endings in metal tubes. I have some fully automated ideas and some different presses but this version that builds on a mechanical excenter is my latest idea. Im thinking it could both be used manually with a arm or it could be connected to a motor and be driven that way..

However, some plastic tube endings are a really tight fit so I really need to make sure a excenter design would work.

My main model attached in this post: "excenterPress"

Can I simulate how heavy the plastic ending is to push? And from that get a read on how much force is needed to turn the axle?

If not, is there another way to calculate it?

And, if its way to heavy, what would be the next step to make it less heavy to turn? Gears? another excenter wheel?

My second model attached in this post: "exenterTest v1"

(This is a different question but related cause of the excenter problems)

One thing I have noticed about excenter designs is that they can fool you. The model is a dummy version I made for this post showing a type of excenter design I have been working on improve right before the holidays. The big curve that pushes the object is the variable that can be changed to get difference in how heavy the axle feels to move. I had to do a couple of different prototypes and test since I don't know the math behind it..

[John_Holtz]

Hi @et.teljemo 

Using simulation to calculate rotating machinery is difficult, in part because the rotation is difficult for the solver (axles, contact, etc.), and in part because Fusion has limited capabilities. My suggestion for the "excenterPress" model where a plug is being pushed into the plastic tube is to model the plug and tube only and simulate pushing the plug into the tube. Of course, this assumes that you have all of the material properties required to describe the stress and strain (mainly for the plug which experiences large deformation). By moving the plug X mm, the simulation will calculate the force necessary to move the plug. Based on the force, you can calculate the torque required to turn the eccentric based on the geometry. (In theory, the torque calculation is a simple hand calculation. Determining the geometry and angles and everything is the hard part of that calculation.) The simulation type would be nonlinear static.

The model "ExcenterTest" is more difficult to simulate because it is all rotation. If the 75 degrees of rotation can be accomplished in less than 0.05 seconds (and hopefully faster), then the Event Simulation study type may be able to solve it. (The Event Simulation runtime is limited to 12 hours which is why the duration needs to be as short as possible.)

Let us know how it goes.

[et.teljemo]

hi @John_Holtz 

Thank you for your reply.

I was afraid it would be hard to accomplish using fusion 360 but I had to ask. Couldn't find any similar simulations on Youtube and if it doesn't exist on YT, it doesn't exist at all 😂

However, I'm really interested in the "simple hand calculation" you mention. I could measure the force required to push in a plastic ending using a manual hydraulic press with a gauge to view the tonnage. (or maybe it shows in "bar")

If I know the force, how to I calculate the torque on the axle? I tried googling a formula for this but google just think I need to know the force tu punch Sheetmetal.

[John_Holtz]

The original model can be split into three separate assemblies for the purpose of the hand calculation: the plug, rod, and eccentric. (Forgive me for not just taking snapshots of the actual model. That would have been way better than my block diagram, but I didn't think of it until I was well into it. 🙄)

• You know the force on the plug, Fp, from measurements.
• That same force acts on the rod. It is counter-balanced by the force Fe which is the force acting between the eccentric and rod. Fp/Fe = cos(a), so Fe = Fp/cos(a)
• The angle a can be determined from the tangent point between the roller on the rod and the eccentric.
• The torque to rotate the eccentric is Fe*D, where D is the perpendicular distance from the rotation point of the eccentric and the line of action of Fe. 
• The torque on the eccentric is either developed by a motor, or from hand power pushing on a lever arm with a force Fh at a distance of R from the axle (torque = Fh*R). Since you know the torque required and the force Fh that you can push with, you can calculate the length of the lever arm R.

Actually, it is probably simple to use Fusion to get the tangent angle a and the distance D every 10 degrees of rotation. Put those results into a spreadsheet and calculate Fe, torque, and R, and you have a nice graph. Note that the shape of the eccentric does not change the procedure. What does change is the contact location, tangent angle a, and line-of-action distance D.

So yes you can use Fusion to solve the (geometry) problem. 🙂

[et.teljemo]

Hi,

I tried turning the model a tiny bit and entered the numbers in Excel.

Would you say it looks right?

I haven't measured the Force (Fp) so I just guessed a number for the calculation.

Also, Fh is the force I use with my arm on the lever right? I just guessed a number here also.

The results if my calculation is done correct is that a motor would need to turn 1438,846 Nm

A 200 mm lever would give me 10000 Nm of torque if I only push it with 50 Kg (This feels wrong)

See table and image below 🙂

Description	Variable	Value
Force on the plug (Kg)	Fp	500
Same force on rod (Kg)	Fp	500
Counterforce on rod (Kg)	Fe
Angle (°)	a
Distance (mm)	D
Lever arm force (Kg)	Fh
Lever distance from axle (mm)	R
			Fp / Fe	Fp / COS(a)	Fe * D			Fh * R
Position	a	D	COS(a)	Fe	Torque	Fh	R	Lever Torque
Angle 1	4,19	2,87	0,99732724	501,3399591	1438,846	50	200	10000

[John_Holtz]

Hi,

Your calculations look correct, but you should calculate Fh based on your assumed R. You only need 7.19 kgf on a 200 mm lever to develop the 1438 mm*kgf torque needed to push the plug with 500 kgf.

If at some angle the hand force Fh is larger than what a person can realistically do, then you need to increase the length of the lever arm R.