A little too long

It's been too long since my last post here, I have been busy with work but I finally have some time to sit down and write out what will likely be a very long post.

The first and most important part of this post if the arrival of the parts I needed to build the robotic arm which I have christened Al. seen here shortly after completion.

There were problems though, several to be precise. the first and most crippling being the lack of torque from the shoulder and elbow joints. I had expected this to some degree but I just didn't know how bad it might be until I had the parts, I could of purchased overpowered servos from the start but I didn't want overkill. I'll look more closely at Al and his upgrades a second post after this one is finished.

The second problem I encountered was giving it a proper power supply. I do own a 30V variable PSU but this lives on the opposite side of the desk I want Al to live on. I did try batteries with little success, the high current from the servo's drained 4x AA Duracell's in about two hours.

The third problem was getting a high current device like a servo to share a common ground with the servo's I did try a separate ground out of curiosity, I had been told it would cause problems for the servo's but I wanted to see this for myself. Turns out the servo's have some sort of robotic epileptic fit if they don't share a common ground, quite amusing to say the least.

LET ME GO!!

Previously in this post Servo Fun I had made a simple circuit to supply power to the servo's while acting as a go between for the servo signal, I had said originally I would eventually take the time to design and build a PCB which would do a better job, and here it is.

One evenings work and a few hours the next day to manufacture it produced this little beauty! the top DC jack is the power supply, this is then split between the Arduino supply jack on the bottom and the servo's.

Annoying enough I only realised afterwards I could of used the copper pour area as a ground plane, never mind though there is always next time. there is a space for a 100uF capacitor in the centre of the circuit for smoothing if I require it, so far I have had no problems with using it although I have noted a few improvements to be made should I need to make another in the future.

Creating a more permanent power supply has taken a little more effort, fr the last 4-5 evenings I have been hard at work building what I have named a Power Distribution Unit (PDU). Instead of having a random cable running across my desk I have developed a box that will live on the underside of my desk which will have multiple DC sockets. I have run a cable along the underside of my desk with two banana's on the end which plug into the PSU.

I have designed it to supply a constant 5 amps of current (or 1 amp per jack). The PSU I own will only supply 5 amps an has its own overload protection, should I connect the PDU to a battery or a power source capable of supplying more than 5 amps I have two fail safes, the first is a 5 amp resettable fuse (the big yellow square) which will break the circuit should  draw a high current by accident, the second is a fuse holder accessed from the front of the PDU which will contain a 8 amp fuse in the event of a short circuit. why have two fuses you ask? well first I like redundancy, should one fail the other will back it up, secondly I don't have a mountain of 8 amp fuses to hand.

Once again I will eventually design another circuit with either a LM317 variable voltage regulator or a selectable set of regulators for providing a more controlled voltage. at the moment the box is designed for use with the PSU but I would like a bit more flexibility.

I will follow up very soon with another post containing more detail about Al and his other subsystems along with several updates on new toys I have acquired.

Have fun and good luck.