The (Driver) Issues
My Prusa i3 really is now becoming a labour of love, rather than something that will ever be useful. Despite my last bout of tinkering, something was still broken. The Halcyon days of perfect prints seem long in the past now – did they ever even exist I wonder? I decided my Polulu-alike (Sainsmart) A4988 stepper motor drivers were the problem – I just did not seem to be able to get them at the sweet spot between too much current (they get hot and shut down) and too little current (they stall).
New Axis Stepper Drivers
I went to the Pololu website and bought 5 of their DRV8825 drivers. These have a Texas Instruments chip on and they can apparently run higher currents with no cooling. They arrived in a couple of days from the USA, with a sticker. Installing was pretty easy: I just pulled out the old drivers (for X, Y and Z – the extruder, touch wood, has not given me problems) and slotted the new ones in.
Actually, it wasn’t quite that simple. After powering up Pronterface I found things were slow and movement distances were halved. Luckily I remembered the whole micro-stepping thing: you have to set this with the jumpers on the RAMPS 1.4 (under the drivers). When I first built the machine I had just installed all 3 jumpers to all three axes. This means that the installed stepper does the best they can do, which is 1/16 for the A4988 drivers. The DRV8825s can do 1/32 which explained the halving I was getting.
The RepRap website tells you which jumpers you need on your RAMPS1.4. Since I had set things up in Marlin as 1/16, and have, at some point, had things running well at 1/16, I went for 1-no jumper, 2 – no jumper & 3- jumper to set the new driver at 1/16 micro-stepping too. I had to do a bit of Googling to work out which jumper pins were which…turns out it written on the RAMPS1.4, just real small (as MC1 to MC3).
Fan support upgrade
I do not really have faith in the DRV8825s needing no cooling, and besides, as a result of my tinkering with the RAMPS1.4 I managed to break one of the soldered connections to my fan. In the process of repairing this, I decided to I build a little frame out of Technic Lego which hinges the fan around (and locks closed with a drop-in pin). Hopefully way more convenient than what I had before for when you need to get at the RAMPS1.4 board.
Dunno yet: haven’t got the nerve to try it. Another day, another post.