I have some more ideas to post. So firstly but very simply, I'm going to try to avoid gears. This is because gears introduce slop to the drives and thus looses accuracy. There aren't many places I can use them any way but places like the Z-slide where I could potentially use one motor for the control and use gears to move the other corners would not be very accurate to 3 stepper motors and a rod for the other corner. The next thing is that as well as ball screws, I will most likely use a bunch of bearings to make other joints more fluid in movement (ie lower the friction). I've started looking at materials for the frames and I think I will try and source channels, angels etc (not the profile for the main supports/legs though) from
Ullrich. I can get these where I live easily and are obviously made out of aluminium. I started last night on designs in inventor but I stopped once I realised I hadn't made my choices on the exact measurements of the frame. I'll post the design from inventor in the next post but for now I'm still deciding on sizes. Here's a picture of the bed, without the x and y slides showing on top.
This shows the dimensions which I'm unable to decide on and some of the features of the frame. I can't decide because I would prefer a 450mm square bed but this would make the outside edge (A) of the frame around 750mm which is very large (assuming C is 50mm). If I make the bed only 310mm square then dimension A is 600mm. Ways of making the excess space smaller is either by radically changing the design which I don't want to do, mount the motors in the outside edges, though this has other problems or try and reduce C as much as possible. I'll make my decision up asap.
On the electronics side again, I've decided I'm not going to use the stepper motors mentioned previously as these use too much current for what I desire so I'm going to change to
these 12V @ 0.33A, 1.8 degree steppers motors. These are cheaper, have a much larger standing torque (not that I need that) and are at a more standard (well popular) voltage. Though that means a worse precision, I can use half stepping or use better ball screws to make up.
One last thing is I realised this morning that the extruder could potentially have a few motors attached but only one would be needed to work at once. This made me realise that I can use a multiplexer to choose which motor I want to activate and control. The reason for this is that it allows the duplication of the PWM channels to be used for all the motors attached and uses less pins on the chip all up.
That's it for now, hopefully by next post I'll have I2C working on my ATmega88 (parts turned up today). From there I'll order some stepper motors and try and build a driver for those.
