Right Arm Update

After a weekend of printing i have enough part to mount the arm to Robbie
to get a feel for how it looks. I have to move the shoulder pan joint in further or
we will have trouble going through doors and change the position of the servos
so they are behind the arm and offset the weight

Right Arm

Since the last update i have rebuilt the printer about 3 time it's now a reprap and prints 20 times faster that the first version. I found a great hand and arm project on thingiverse inmoov i have the most of the major parts printed just waiting on some servos and free time to start programing 

First Printed Parts

Its been awhile since the last post the printer is finished and working
the threaded rods i use for the X and Y axis make the printer very slow, but at least it works. To use the printer to its full potential I need to learn cad and openscad which all takes time the first parts are starting to find there way
on the robot the orings i used to sync the castor angle and potentiometer didn't last long and tended to slip off, replacing them with gears seams to be a natural choice the only snag is reverse the pot power connections  to make up for the change in direction when using gears. I mover the MCU from the side pod
to under the torso (which has been hinged to provide quicker access). The wiring has also been cleaned up to provide better reliability. I finally completed the drive motors by adding the last motor controller and encoders now its a true holomonic drive, but i fear we have run up to the limit of the AtMega I'm having a lot of trouble tuning the PID loops (8) stearing works fine on it's own but when i  add the drive velocity control  the steering starts to drift

Progress Report

Its been to long since the last update testing is proceeding slowly localization is improving, rotation is still a problem. Increasing reliability has been one of the  goals  and improving the design to achieve this requires a 3D printer so i can make the custom gears and brackets. So i started making the printer that can double as a milling machine for milling parts and PCBs.
The printer uses draw runner as sliders they work rather well the NEMA 17 stepper motors may be a bit small but they will do for testing later they can be used in the base as steering motors

To Arms

No not a battle cry but what good is a robot with out arms if you noticed Robbie has a arm but with the AX12 servos and springs it can barely move and the shoulder lift servo will over heat quickly even with out the extensions. The price of larger servos is not an option. The torque required for a arm 90cm long to lift a 2 kilo object is over 1000 Kg/cm for the shoulder lift joint. After a bit of research i think i will use stepper motors at least i can start out using some of the old stepper motors and gears i have lying around. I plan to use the steppers for the first 4 joints in the arm at the moment just using motors from a old printer and a arduino to interface with ROS

Navigation Testing

A video of Robbie driving around under joystick control to test localisation
it works fine but after a while he gets lost

Improvment

Over the last couple of weeks I have been hard at work refining the control, localisation and general drive functions. While we are not at the stage of autonomous navigation short runs will work. The big fix is still odometery and how the base responds to navigation commands from ROS, The steering is always "fishing" for direction causing the robot to dart from side to side