# Step 2: fixing transfer function errors¶

## Context¶

At this point you have observed that the brain is spiking somehow. The robot does seem to have all ROS topics correctly loaded, but apparently, brain output and robot wheels may not be connected properly? We will inspect the transfer functions and find out if one could be faulty.

## The Transfer Functions Editor¶

Open the editors tool and go to the Transfer Functions tab. On the left, the transfer functions are listed and we see one that is not activated (linear twist). Click to edit the function, and you will see the error Parameter right_wheel_neuron was not mapped properly. Indeed, the function linear_twist expects an argument right_wheel_neuron, but there is only one decorator and it maps left_wheel_neuron.

We need to write another decorator for the right wheel neuron. Your transfer function should now look like this:

@nrp.MapSpikeSink("left_wheel_neuron", nrp.brain.actors[1], nrp.leaky_integrator_alpha)
@nrp.MapSpikeSink("right_wheel_neuron", nrp.brain.actors[2], nrp.leaky_integrator_alpha)
@nrp.Neuron2Robot(Topic('/husky/cmd_vel', geometry_msgs.msg.Twist))

def linear_twist (t, left_wheel_neuron, right_wheel_neuron):
return geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=20.0 * min(left_wheel_neuron.voltage, right_wheel_neuron.voltage), y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=100.0 * (right_wheel_neuron.voltage - left_wheel_neuron.voltage)))


Press Apply and activate the function.