"Spaceshuttle" starts spinning violently after booster separation

[UncleManuel]

Hi!

I legoed together a Spaceshuttle clone and noticed some unwanted behavior.

 

After booster separation at around 20000 meters the whole vehicle starts to oscillate then roll violently and uncontrollably. No matter what I do the centrifugal forces will ultimately rip the external tank off... 

Sooooo, the big question is: why does it behave like that? 

[ph0x]

I don't see an engine on it...

[Fierce Wolf]

More struts? Sepratrons to push away the boosters?

[linuxgurugamer]

Off center thrust.  The thrust centerline is above the CoM, so that starts the spinning.  
keep in mind that the shuttle does not fly straight ahesd.

The following is a good explanation by Scott Manley of the changes in the CoM of the space shuttle and the different thrust vectoring available in the engines involved

k

 

 

[drpunk]

I'd hazard a guess at centre of mass and centre of thrust.

Both change drastically without the boosters

Edited November 22, 2019 by drpunk

[UncleManuel]

The weird thing is that it spins on the roll axis, not the pitch axis... 

Takeoff can be a bit wobbly on inclination change but the uncontrollable spinning occurs after booster separation.  I really don't understand why it's rolling around the vertical axis like that...

[linuxgurugamer]

3 minutes ago, UncleManuel said:

The weird thing is that it spins on the roll axis, not the pitch axis... 

Takeoff can be a bit wobbly on inclination change but the uncontrollable spinning occurs after booster separation.  I really don't understand why it's rolling around the vertical axis like that...

Video would help.  Also, the craft file

[CBase]

In your screenshot RCS is not enabled, although you have RCS thrusters at the nose. Without RCS engine gimbal will counter any derivation from course as control surfaces get less effective at altitude.

Be aware that roll and yaw are connected if controls are off axis with center of mass.