Simscape Multibody will not move

Hi,

I wonder if anyone may be able to help. I'm constructing a landing gear model and have added a virtual runway underneath the model. Where the wheels dropped down and settled before, they no longer drop (see pictures) since adding the runway. The landing gear is a imported cad model, where the runway has been implemented as in the code below. I was wondering if it because of a difference in the datums? Does anyone know how to make the wheels drop so they sit nautrally on top of the runway? My next stage is to apply force from the virtual runway upwards, so I can measure movement within the landing gear - with a view to calculating stresses within the frame if this is possible.

Kind regards,

Andy

Answer 1

[Steve Miller]

Hi Andy - you appear to have rigidly attached your wheels to the platform and to the World frame. Your landing gear should be connected to the World frame only via a joint (Prismatic, 6-DOF, ...) and your Platform should be connected to World via a Rigid Transform.

If you post the entire model we can check it more closely.

--Steve

[Andy Wileman]

Hi Steve,

Thank you for getting back to me once again. Yes, I think you could be right, I've attached the model so you can have look. I had a lot of trouble lining up the platform under the wheels (in Solidworks you can just bring both surfaces together, but to use the coordinate system e.g. translation and rotation was difficult - maybe there is a simple way).

It's a slow process converting to Simscape Multibody for me, but I really like what the software can do. I've been trying to follow the tutorials and examples on https://uk.mathworks.com/matlabcentral/fileexchange/55494-physical-modeling-for-formula-student-introduction-to-multibody-simulation as they have simulated a similar situation but for a car.

Can I also ask, where I have used a solid tyre in my model, is it possible to simulate the inflated tyre? As aircraft tyres are usually inflated to a high pressure with nitrogen and it would be intresting to see the affect of damping from the tyre due to the impact of landing.

Once again thank you.

Kind regards,

Andy

[Steve Miller]

Hi Andy- I am missing all the geometry files, so I cannot look at your model.

For tire stiffness, if you put a Prismatic Joint (or other joint) between the tire and the ground platform, you can use joint limits to specify a linear stiffness. You can also use the Spatial Contact Force block to specify contact between shapes.

--Steve

Answer 2

[Andy Wileman]

Hi Steve,

Thanks for getting back to me. This should be a straightforward! I've followed your advice about inserting a prismatic joint etc. and frustratingly it is nearly there. I've been trying to follow the Matlab suspension tutorial as well, I suspect the problem might be lining up the platform (which is defined on the World coordinates) with the CAD model.

I have attached all the files including the geometry, I would be very grateful if you can take a quick look.

I will also tru the idea with the tyres as you suggested if you can get the model working.

Kind regards,

Andy

[Steve Miller]

Quite close! I have added frames at the wheel centers and used joint limits in a 6-DOF joint to model the contact between the tires and the platform. I had to re-orient a few frames along the way. Model is attached with some annotations to indicate where I made changes.

--Steve

[Andy Wileman]

Hi Steve,

That's absolutely brilliant, I don't think I would have got there on my own. I can't thank you enough - I've been on this all week.

Kind regards,

Andy