Hi all:

I’m trying to control a system using acados for python. I want to impose a constraint for the velocity of the system in body frame, so I need to use a non-linear constraint, at it depends on the attitude of the system.

I have tried but I doesnt work. I tried to simplify by imposing the constraint in the global frame like this:

```
ocp.constraints.idxbx = np.array([21])
ocp.constraints.lbx = -np.array([1])
ocp.constraints.ubx =+np.array([1])
```

Like this it work perfectly, as I define it as a linear constraint.

Then, I tried to apply the same constraint but using the non-linear definition of acados (as an intermediate step before imposing the velocity constraint in the body frame). The code that I used is:

```
ocp.model.con_h_expr = model.x[21]
lb_vh = -np.array([1])
ub_vh = +np.array([1])
ocp.constraints.lh = lb_vh
ocp.constraints.uh = ub_vh
```

It does not work. I do not know why, there is no sense for me as the constraint is the same. The solver settings are:

```
ocp.solver_options.qp_solver = 'PARTIAL_CONDENSING_HPIPM'
ocp.solver_options.hessian_approx = 'GAUSS_NEWTON'
ocp.solver_options.integrator_type = 'IRK'
ocp.solver_options.sim_method_newton_iter = 10
ocp.solver_options.qp_solver_iter_max = 300
```

My model includes algebraic equations so I need to use the implicit formulation.

Thanks a lot!