Meet Al

   Here is the long overdue post introducing you to Al the robotic arm, I think its been just over a month now and a great deal of progress has been made in his development. I want to go over the hardware specs in this particular post though, something i have not yet done and promised to do quite a while ago.

   First off is the delivery that made this all possible, I had ordered quite a few parts some of which would be surplus to requirements because the pieces are sold in packs of two, not a great problem as spares are always welcome and I'll be using another set of Servo Erector Set (SES) parts when I build the second arm to compliment this one.

  

   Al had two primary building phases, the first used the parts shown in the picture below. I seen discovered that even when the servo's were running at their maximum 6V they were woefully under powered. The second building phase involved purchasing several new parts and a much more powerful shoulder servo.

  In the first phase the joints all used HS-422 servo's except for the shoulder which uses HS-645MG.

                        HS-422            HS-645MG

Speed              0.16sec                 0.2sec

Torque           4.1Kg.cm             9.6Kg.cm                   

Turns out blogger dons't have any spreadsheet style ways of displaying information...

   The first phase of construction took me a good few hours, instructions are available on the Lynxmotion website for certain models and building techniques but none for the type of arm i was building. I had to reverse engineer a image that i was basing mine on.
 
   One serious problem I ran into without instructions was the order of construction, I made the mistake of starting with the gripper when I now know I would of been better off building from the ground up, a second problem I faced was ordering the wrong servo mounting brackets, there are few types of each bracket available and I didn't realize the importance of the correct one at the time of ordering.
 

   About a week later after I had received the second wave of parts I began the second phase of construction. The upgraded shoulder servo is a HS-805B+, This boasts a impressive 24.7Kg of torque at 6v as well as a equally impressive speed of 0.14sec per 60 degrees of motion. With greater power comes a much bigger servo as you can see below.

   The new servo brackets are equally impressive compared to their normal sized counterparts. They are all made from high quality anodized aluminium. The brackets have a brushed finish, weather this is intentional or not I don't know but it adds to the appearance quite nicely.

   There are still a number of problems that I must deal with before I can declare the arm fully finished, The most pressing matter is the oscillation created by the larger servo bracket. When the arm is held out it picks up a slight bobbing motion because of the small amount of flex in the servo bracket, The servo tries to correct the small moment which only results in the arm bobbing a little more. There is a special dampener available which applies a small amount of friction the the servo bracket to remove the oscillation. Annoyingly the supplier in the Uk seems to forever be out of stock of this part and ill be dammed if I'm paying £20 for delivery from america for a £5 piece!! I have been forced to start searching for something to make it from which is not as easy as it sounds, the material must be wear resistant, 2mm thick and have a tacky surface.
   Other problems are easier but will require a little thinking to achieve a tidy elegant appearance. The cables need to be sheathed and tied down so they do not become caught in the brackets.
 

As proud as ever

   The hardware needs to be organised better so it does not simply form a knotted mass on my desk.

   Last but not least Is Al in action following a simple pre-programmed pick and drop, I was trying to make the movements as smooth and quick as possible, I have made a few more adjustments since recording this and I'm somewhat happy, I'm sure I can make further improvements though.

Its getting later here and i apologies for any mistakes I have made, I've checked it over but I'll have another look in the morning to be certain.

First Life

I know I said I would make another post in more detail and I do intend to, I've just been a little distracted by the developments I have made in recent days. At long last its following pre coded commands to stack a simple pile of blocks... in a very angry fashion.

Since recording this I have made use of a new servo Library made by one of the kind chaps over on the Arduino forums which allows me to control the speed of the servo's. something that should reduce the angry movements to a more manageable pace.

A little bit for now.

   I'm lacking time again so here is a older video of the arm in action, this was made before the servo and power supply upgrades so it really is in its infancy here.

   It's following a simple set of  Servo.write(##);  commands programmed to the Arduino so nothing special for now.

   I did finish a basic set of control knobs yesterday which I will show off in the promised post covering the arm in more detail.

Have fun and good luck.

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.