Friday, 28 December 2012

Adding Feedback

Added a position feedback using the potentiometers from the servos
the voltage appears to be .5V to 1.85V I connected this to the analog pin
and mapped the values to 180 using a range of 0 to 500 the angles shown in RVIZ look to fairly close but the joints jitter about 10 degrees I tried using the Aref pin and supplying 2 volt with a voltage divider but this doesn’t seem to work giving me a reference voltage of 0 ? I'm running a smoothing of 20 while it helps its still not good enough.

Thursday, 27 December 2012

Arm Control

Now that we have arm that works it time to start controlling it at first i will only controlling the arm not the hand ( I don’t have enough servo pins in in the adruino and have to wait until  i get a mega). We have a hacked driver that controls the arm joints by publishing a topic to the joint i.e.
rostopic pub -1 /Right_lift_joint/command std_msgs/Float64 -- 0.5
which moves the right shoulder lift joint to 0.5 radians. Radian are a pain to visualize so we have a model in RVIZ so we can see what is happening.
Joining the stl's in freecad only works in windows when I have more time i will add the other arm and add all the parts i think it looks good with the arm transparent seeing all the parts. The driver lacks real feedback  (hobby servos don’t have feedback) this will require another hack, the upside at the moment is feedback is the last commanded position this makes for a simple simulator. I have hacked a action server and i can send a sequence of poses the action server will run 1 pose until its complete (when feedback uses the actual position not the last commanded position) then move to the next.
The printed parts have held up  well with only a few breakages the main problem is PLA is too brittle now that i have the hang off printing ABS I will remake  the parts (the junk box of broken and obsolete parts is growing).
Next  milestone is a video

Sunday, 2 December 2012

New Shoulder Joints

After Seeing Inmoov's video I liked the way his shoulder moved and the bearings and drive system that i required made the original set up very jerky and hard to get a accurate placement here is a photo of the new joints I have removed the lower arm for the moment until the new joint works smoothly The actuators were some old trim tab actuators i had laying around with the gearing they should have about 150 Kg/cm torque the code is very similar to the steering and drive functions of the base with a 2 stage PI controller it moves very smoothly. The left arm should be finished next week then I need work on how to attach the shoulder and  head.