I have been experimenting with making my Robot Arm mobile. The first incarnation of this was to give it wheels. Whle this worked fairly well, it had problems with carpet and stairs.
My next idea is completely mad, and if I pull it off will be very spectacular. I am putting the robot arm on 28 hexapod legs. This is going to mean i will need to use nearly 50 servos to carry the weight, and distribute the load.
The first attempt caused near fatal breakage in the servos. I severly underestimaetd the weight distribution needed to support the arm when it is fully outstretched. I anly used 20 servos, and although this was good while the arm was in it's parked position, it was not nearly good enough for carrying the weight when the arm is in use.
Each leg is half a meter long when fully extended, making this thing a massive monster.
There are few things I will be doing to make this experience a little easier on myself, detailed here.
Leg placement when arm is in use
Much like a crane extends its legs when the boom is in operation, so will I. I will use the OpenServo platform to detect and calculate leg placement. I will create a host controller for groups of legs, and using cooperative computing, optimise leg placement for optimum weight distribution, and least strain on any servos. Legs can extent outward very quickly to overcome any balance issues.
I may even lower the main body platform to the ground to gain higher stability.
Center of gravity
The weight of the robot is immense. I will have to counter balance this when I need to move the robot around. I will design the new hexalegs in such a way that it's not too heavy, yet gives a low center of gravity.
Batteries are heavy. The amount of juice needed to run the robot arm is hugh. I am currently powering the arm from a 12v motorcycle battery, and this is a beast.
The servos will require nearly as much power as the main body, to overcome this problem I have butchered a servo, squeezing a high current capacity battery between the potentiometer and the driver board. The OpenServo v2.1 design has provisions for battery voltage measurement, which when becomes critical can be recharged from the main battery. Using a novel voltage switching circuit I am able to route power from the most optimum source for the task needed. The motors can run from the main 12v source until there is sufficient juice internally to continue. This self charging and self power routing method is very useful. If the systems detects there is not enough power to continue using all legs for movement, and can disengage unneeded motors, it will. It can bring them back into use for trickier uneven surfaces.
See servo modification page for more details.
The main robot is make of steel and aluminium. This makes is heavy, but strong.
The legs have no real need for this tensile stringth, and can be constructed from aluminium. The weight saving will help counterbalance the additional weight from the modified servos.
All in all, this should be an impressive looking machine. Once it has a full complement of sensors it should be safe to be near too. (It's lethal at the moment).