Signals

I am working on a dynamics simulator for an underwater vehicle to be run in the Robot Operating System (ROS – www.ros.org )  The purpose is to be able to completely simulate an autonomous underwater vehicle (AUV) in ROS and then use that same code to control the actual AUV in the water.  Obviously, a variable switch will be used to designate whether the software is running a simulation or actually being tested in the water.

I am using the Boost odeint library ( http://svn.boost.org/svn/boost/sandbox/odeint/ ), which unfortunately, required a manual install on top of the regular Boost libraries.  Odeint is really quite easy to use, almost as easy as Matlab’s ode45 and Octave’s lsode ordinary differential equation solvers.  In ROS, I have the simulator loop at a specific rate (ie. 10 Hz) and I only have the ode solver compute one step every loop.  I ran into trouble using the Euler step method with a slow loop rate, but either increasing the loop rate or using a better ode algorithm (ie. stepper_rk4, stepper_midpoint) resulted in proper results.  In order to test my basic setup, I simulated a pendulum swinging back and forth.  Here is a screen shot of the pendulum simulation in Octave…

Octave Pendulum Simulation. Top plot is pendulum height, bottom plot is pendulum velocity.

I compared the Octave simulation, which I know is valid, to the ROS simulation of the pendulum, which is shown below.

ROS Pendulum Simulation. Top plot is pendulum height, bottom plot is pendulum velocity.

Now I just have to figure out the differential equations for the underwater vehicle’s motion and I will be able to simulate that in ROS as well.

I recently purchased a the AKAI APC20 for my Ableton Live setup. When I was at the music store purchasing the controller, the guy at the counter suggested that I purchase the $15 store warranty. However, I declined since I figured that if I wore out the pads on the controller, it would warrant buying a higher quality controller and in a year a newer one will be out anyway. Unfortunately, when I got home I discovered that one of the pads was already acting strangely! It would get stuck and it didn’t have the same feel as the other pads. I was in a dilemma: drive the 30 min back to the store, or take apart my brand new APC20. Take it apart!*

*Disclaimer: This will probably void your warranty, so don’t do it =)

I actually took the APC20 completely apart before taking a photos, so even though I am going to display the photos backwards, as if I am taking it apart. Time warp.

AKAI APC20 - Before Tear Apart

First, remove the 12 visible screws on the back of the APC20.  Then, the 4 rubber feet have to be removed.  The rubber feet are held onto the APC20 with a combination of two-sided tape and the rubber stoppers have little plastic pieces that fit into holes.  Thus, you can remove the rubber stoppers without having to re-glue them back on later. I like these rubber feet.  Remove the screws under the rubber feet as well.  You DO NOT have to remove the silver hex screws that are visible from the front.

The Rubber Feet pop off just nicely.

The APC20 cover will then come apart quite easily from the back of the APC20, BUT! be careful you don’t break any cables that are connected between the front and back panels as shown in the next image.

After removing the cover.

At this point, you have to remove the screws that connect the PCB to the back panel.  There  are quite a lot.  Most chips these days have great ESD (electro-static discharge) protection, but make sure not to run around a carpeted room while pushing your finger onto any of the parts.  Also, there are two screws that are slightly hidden under the ribbon cables.  These are used to remove mechanical stress on the ribbon cables.  Next, you will have to remove the Cue Level potentiometer and level selector knobs.  These pop off really easily.

Pop 'em off!

Also, you will have to remove the washer under the Cue Level potentiometer.

Remove the washer!

At this point, you should be able to remove the PCB from the back panel.  If the PCB gives you any resistance, then you probably missed a screw.  Be careful.  Once the PCB is out, the pad is now visible.

The AKAI PAD in all its glory.

Very Bendy!

Front side of PCB

After I had taken the APC20 apart, I discovered that the capacitor displayed in the next photo (the larger left one) was the offending part.  It was interfering with the operation of the pad.  To fix this, all I did was move the capacitor slightly away from the pad, problem fixed!

The capactor was the problem!

When replacing the pad, take the time to really smooth it out!

APC20 Front Panel Only

USB Chip, power regulators, & microcontroller to process button presses.