Robotics...

This is not review of the Phenoptix MeArm as such. It is merely my thoughts on the device, warts and all, for what it is worth! I am in no way affiliated with Phenoptix!

I first came across the MeArn by Phenoptix by pure accident and decided to purchase one because I considered that it offered a workable first step on the robotics ladder at a very reasonable price.

Once ordered, the kit of parts arrived quickly albeit with one small part missing, but the guys at Phenoptix sent a replacement in the post without delay.

Photograph courtesy of Phenoptix

The version of the MeArm that I purchased is shown on the left and I have to say that I was impressed with the quality of the parts which are all laser cut from a single sheet of plastic. Four x 9g Hobby Servos completed the package as well as a bag of nuts and bolts to hold it all together. The MeArm can be purchased in a variety of colours and combinations of hardware, for example, you can buy the MeArm with or without the servos if you so wish or without the nuts and bolts.

The instructions were downloaded from the Phenoptix.com website and I had little difficulty assembling the kit, completing it in just over an hour. I have only two criticisms of the MeArm and the instructions are #1 on my list.

Please don't get me wrong, as instructions go, the MeArm ones are pretty good but they need some polishing as some areas are a little unclear especially where the reference photographs are concerned. Nevertheless, I managed to work out what was required.

I would like to stress that it is vital that you check that all the parts are in the kit and that you identify and confirm that all the nuts and bolts are correct before starting to assemble the kit. It is possible to use the wrong length of bolt if you are not careful which will make life difficult later on.

The geometry of the linkages is clever and obviously took a lot of time and experimentation to get right. Two servos are used to control the Y & Z axis of the arm with a Third servo controlling the claw on the end of the arm. A fourth servo is used to control the X axis and this is where I raise my second criticism.

The whole arm assembly rotates on the shaft of the servo in the base of the assembly and it wobbles! This is a single point of failure in what would otherwise be an exceptionally stable and strong assembly. If only some form of additional support for the arm assembly could be added although I am sure that the hobbyist could fashion something from their junk box.

The rest of the assembly is surprisingly sturdy with little or no play in the linkages but be aware that there are no bearings on any of the joints which comprise a clearance hole in one part and a threaded hole in the other half of the joint. This is not an industrial robot and I am sure that no one would use as such so the joints will probably give good service for average use.

Phenoptix provide a range of software to control the MeArm and there is even a controller unit with Joy Sticks which can be used to operate the MeArm and record the movement if necessary. It must be remembered that all movement is made by simple Hobby Servos as used in Radio Control and other remote control systems. Reproducing movement is always going to be a compromise. If you are expecting positional accuracy to fraction of a millimeter you will be very disappointed but, despite this limitation, the MeArm is surprisingly accurate.

I have toyed with the possibility of replacing the servos with geared stepper motors and when I get the time I will go down this route but, for now the servos do the job.