[Sticky] NEW FOREARM: for everyone having problems tightening the timing belt (STL files attached)
#define ROBOT_ARM1_LENGTH 91.61 //92.84 FIRST SEGMENT <-IF THE DISTANCE MEASURED IS 1mm, change the value from 91.61 to 92.61
#define ROBOT_ARM2_LENGTH 105.92 //106.79 SECOND SEGMENT
Some photos of the new forearm below as a reference
This is perfect timing for us! We got to this point in assembly last evening. I think we will go ahead and swap this out now while it can be done easily.
I was a little skeptical about getting the bearing out of the old pieces and put into the new printed parts but it was not to bad. I found that putting the bearing on the table and then pressing with your palm on the part you could easily get the bearing into place.
I will say that the belt is still loose and that I think instead of printing two pieces that it should be one piece just made longer for those people that have the longer belts. The bearing that is on the bottom of the Elbow is not adjustable and needs to move out with the elbow.
So making a piece that is designed to be longer would fix that and make the belt a better fit all together.
The problem with enlarging the forearm too much is the stability of this element when moving. We are too close to get into the “resonance” distance due to forearm mass and inertia. We have tested longer arms and when “drawing/ writing” it starts to lose its accuracy (shake while performing certain movements). The 280mm GT2 belt, should be 280-ish belt. Right now, even a 281.3 mm belts can be fitted with the new design but not more than that.
Regarding the tightness… The forearm belt, actually, should be a bit loose. There are no horizontal forces that could compromise the precision of the arm and a 280mm belt does not suffer from “elasticity enlargement”. Besides that, as the robotic arm has been 3D printed… well, an overtighten belt will, in the long run, worn out the plastic parts
Mike, thank you for your feedback. Really. The experience and feedback of other Makers like you encourage us to keep improving the robots!