Plot velocity and acceleration vectors of a space curve

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I'm having trouble plotting the velocity and acceleration vectors of the following space curve (r3).

May anyone help guide me in the right direction to solve this problem?

var('t')
r3(t) = (cos(t/2), sin(t), t/6)
v3 = diff(r3(t),t)
a3 = diff(v3,t)
curve3 = parametric_plot3d(r3(t),(t,0,4*pi),thickness=0.5)
velvecs = Graphics()
accvecs = Graphics()
for k in range(9):
    velvecs += arrow(r3(k*pi/2),r3(k*pi/2)+v3(k*pi/2),color='red') #Line 26
    accvecs += arrow(r3(k*pi/2),r3(k*pi/2)+a3(k*pi/2),color='blue')
show(velvecs+accvecs+curve3,axes=False)