01/01/2017 at 11:11 •
Not forgotten lol
I will write an update soon about iteration 2 above and then I have to 'do the math' and after that will be iteration 3 which I will explain when I get back to this project shortly.
11/20/2016 at 02:49 •
OK, I have encountered some problems with the mechanics.
The first was the floppy arm lol. One arm was used as a guide when drilling the 8mm holes for the motor shafts so it was a bit of a loose fit.
I kept tightening it but eventually the Stainless Steel M3 screw just snapped so I found some bolts at the hardware store and upgraded them to M5.
The next problem was binding of the bearings to the hex shaft so I added some spacers. These spacers are still a little to large so I have ordered some thin tube to make spaces with a smaller outer diameter.
The original setup was line this -
Now I have removed one of the hex shafts to make way for the spacers. I also files the middle section of the hub flat to make it easier to mount a motor.
Also the original power supply was intended for the smaller stepper motors that I was first using and it only had the capacity to drive one of the new steppers so it had to be upgraded to -
11/13/2016 at 05:35 •
Now that I decided on some steppers it's time to start putting the mechanics together.
The arms (bicep) are 20x10mm hollow box section aluminium tubing 2mm thick with an 8mm hole at one end for the stepper shaft and a 5.5mm hole at the other end and M3 bolts for tensioning at either end -
The slots at the ends were made with a hacksaw but that didn't remove enough metal at the shaft end so I enlarged it with a abrasive cutting disk. I held the box section in a vice and was very careful as it was very 'grabby' -
The other end is a bit more complex as it holds the separated linkages (forearms) so here's the sequence to making them by using hex standoffs and screws with the heads cut off -
And one arm finished - rinse repeat -
Ok, not the base and motors. I used a round piece of custom board that was left over from another project that I don't remember anything about except that it had round bits. It's too thin (3mm) and it flexes but it will do for now -
You can buy brackets if you want but they aren't hard to make.
Wait!! WTF was that (above) ??? Lets have another look -
Know what it is yet?
Well obviously it's the center hub to hold the end effector now but what was it previously?
It was the center hub from a camera tripod. You can pick up camera tripods for next to nothing in the charity stores because people loose the shoe for them.
OK. Now we prepare these -
Just make them all the same length and use some lock nuts -
Now attache these ends -
And then these ends -
I noticed this to -
As stupid as this may sound there may be some advantage to inverting the forearms. I will 'do the math' and see if my suspicions are correct.
OK, now I have to work out how to do the limit switches.
11/13/2016 at 04:36 •
This is just a fun project that I am doing for the fun of it so there have been several FAILs along the way as nothing is planned out.
First I started by using some very small NEMA 17 steppers I had lying around -
They have very short output shafts so I attaches the arms like this -
I did have screws to tension the box section to the shaft but it wasn't good enough and the fitting was sloppy because the shaft didn't go through both sides of the box section.
Plan 'B' was to use solid arms instead -
That solved the issue with the 'play' in the connection but now the motor didn't have the strength to lift the solid aluminium arm.
Plan 'C' was to use a coupler and separate shaft and bearings with the hollow box section, I don't have a pic of the bearing box -
This actually worked to my surprise. The coupler absorbs the force and applies gradually so that the motor overcoming the momentum. Without the coupler the stepper can't over come the momentum of the long arm.
Well dammed if I am going to make 3 custom shafts on bearings so I went with these motors from ebay -
They're a NEMA 17 1.8°/step, 200 steps per revolution for the stepper, with a 14:1 planetary reduction gearbox giving me about 2,800 full steps per revolution on the final out put shaft.
I am hoping this is problem solved *but* I have noticed some play (not backlash) on the final output shaft so I may end up having add a separate shaft on berrings anyway.