Model toppling when velocity is given

[Venk1]

Hi,
I have a simple design..6 wheels, links connecting them and a carrier box on top.
2 wheels in front, middle and rear.

The problem is my whole model is toppling or jumping too much (don't know why). I gave angular and transverse velocity for the wheel parts.
The rear wheels jump high sometimes, sometimes it is the front, while the rest are on ground pulling them down.
It is so happening that for a given velocity the jump is less (it is coming to ground with a little detour) but sometimes the whole body jumps and as a result the model is upside down.

Is it that there is a fixed ratio of angular : transverse velocity. Please help me with this problem.

 

[GregLocock]

I'm assuming this is in ADAMS View

To be honest your problem description is lousy, but there are several things you can look at. have you set the initial velocity of each part, both translational and rotational? Alternatively what does your model do if you start with it stationary?

Next, how are you modelling the tire to ground interface?

Next, do you have any compliances and damping in the model?

is your ground surface smooth?

if you export your model as an adm file and post it I may take a look a look at it.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Venk1]

Thank You very much for the reply

Sorry for the description..to answer you
I am using ADAMS View, I have set both the translational and rotational velocities but only for the tires. I used 'fixed joint' to join other links.

Under special forces I used 'contact force' between the wheel and ground. There is no compliance or damping and the surface is smooth (negligible friction)

Just to be a little more clear I did not use the tire option..I used the extrude command for wheels (extruded a circle I drew).

Sorry but I did not understand what you meant by starting it stationary. Anyway I removed all the velocities and simulated. It just remains in its position.

I want to basically move my body forward so gave some velocity to the wheels which will inturn pull the whole body forward. (I used right click < modify < initial velocity conditions).

I am an amateur so please bear with my questions and description. I am only able to upload a screenshot

 

[GregLocock]

That's Sojourner isn't it? You'll be glad to know that a model like that works well in ADAMS, but I use compliance and tires. Start with your stationary model, and then apply a torque between two-six wheels and the suspension arms. This should accelerate the vehicle, and simplify the issue with initial velocities.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?