## General Mechanical

#### Rigid Dynamics – Cycle

• TimoK
Subscriber

Good morning everyone,

I am new to working with the rigid dynamic tool in Ansys and i have the following question about the Joints. In the following picture you see my experimental setup for the analysis. Acting force is a 70kg point mass on the bottom backet of the frame.

The axis from the rear and front wheel are fixed to the Ground are revolute joints for the front and back frame sections. My question are concerning the joints 1 - 6 in the middel of the frame.

1:                                                                              2:

3:                                                                                4:

5:                                                                                6:

The Joints are defined right? I have Problems to definde the Referenced and Mobile part of the Joints. What must be reference and what must be mobile?

If i analyis the Force in the spring i get the follwing diagramm. In my opinion the maximal Force with 2200N are to high for a Point Mass from 70kg.

Spring stiffness: 30 N/mm     Spring damping: 0,8 N*s/mm

• peteroznewman
Subscriber

Hello TimoK,

Yes, all the Revolute joints look correct.  It doesn't matter too much which side you call Reference and which one is Mobile.

Is the spring/damper between points 1 and 6?  It looks like there are bodies attached at points 1 and 6, so I am unsure.

I don't see what points are connected to ground. If the front wheel axle was a Revolute Joint, the rear wheel axle can't also be a Revolute because there may be a small motion along the ground when the weight is applied.  What is the joint on the rear wheel axle?

If you want me to see the model in detail, you can use File, Archive and create a .wbpz file which you can attach to your reply after you post it.

• TimoK
Subscriber

Good Morning Peter!,

At first, thank you for the fast answer! In Attach the Archive file from this Setup! The Spring is between Point 1 and 6. I have also problems to define the Spring.

The Spring has an effective lenght of 75mm before the spring drive on block. I used the translationally joint between 1 and 6 to define this lenght with stops.

The restrain geometrie and joints are used in another setup. Pls ignor this.

Thank you soo much for you help!

Greetz TimoK

https://www.dropbox.com/s/kirsp9bwzeoi2hn/Projekt_Daten_70kg_Trettachse.wbpz?dl=0

• peteroznewman
Subscriber

I suppressed the front axle, and created two joints in the Ground folder. A revolute for the front axle and a General joint to fix Y displacement only. This lets the frame move in a natural way that you can see if you animate the results.

I'm getting a similar result for the spring force. The frame+point mass = 99 kg.

Attached is an ANSYS 2019 R2 archive.

• TimoK
Subscriber

Good Morning Peter,

At first thank for you advice and time! I have to accept that the force result is right.

For the next step I will simulate that the cycle falls from 2m to the ground. I now that it is possible to do this in transient dynamics but I will find out what is possible in rigid dynamics tool in Ansys. For this setup I create joints for the tires and fixed the Ground.

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I also create a frictionless contact between the tires and the Ground.

• peteroznewman
Subscriber

Hello TimoK,

You can hand calculate the spring force in the statics problem by drawing a Free Body Diagram of each link in the mechanism.

Read this discussion for some guidance on a way to simulate the results of a drop test. Don't worry about the bike falling sideways.

In other software I have used, it is very simple to assign an Initial Velocity to all the bodies in a dynamics model as an Initial Condition. I am disappointed that ANSYS makes the user jump through hoops to create this condition, except for Explicit Dynamics, but you don't want to use that for this model.