Like Nophead said, backwards wiring on the endstop means you probably shorted 5V to ground. The 5V on RAMPS is supplied by a linear regulator on your Arduino Mega. That linear regulator gets its 12 V through D1 on the ramps board. So either D1 is blown, or your regulator on your Arduino is blown. Checking D1 is pretty simple with a decent multimeter. If it has a diode drop measurement on itby KSevcik - RAMPS Electronics
Your observation on the A4988 whining makes plenty of sense when you start looking at how it works. It's a constant off-time driver, so the set off-time determines the maximum switching frequency. When it's putting out a higher current, the driver has to stay on longer, which lowers the switching frequency. Plus, the A and B sides of the driver are nearly guaranteed to be switching at differenby KSevcik - RAMPS Electronics
The drivers should be more or less identical, aside from the extra heatsinking on the SureStepr drivers. The difference would be with your steppers. I'd offer an opinion, but I don't know if you're running the keling steppers in series or parallel. Also, the specs listed for the QU-BD steppers don't make any sense. They say either 1.2A or 1.05A at 10.5V, with a resistance of 3 (ohms?). 3 ohmby KSevcik - RAMPS Electronics
I think running those DRV8825's at 35V is likely to seriously screw up your micro-stepping thanks to the higher voltage and their rather long minimum on-time. It's similar to the issue Nophead describes with the A4988 here: http://hydraraptor.blogspot.com/2012/04/stepstuck.html The DRV8825 has a minimum on-time of 3.75μs with an effective off-time of around 30μs (It's fixed frequency, not fixedby KSevcik - RAMPS Electronics
I suspect that part of your problem is that you're missing several microsteps due to the high voltage you're running and the rather long blanking time on the DRV8825 drivers. Something similar can happen with a stock A4988 as explained by Nophead here: http://hydraraptor.blogspot.com/2012/04/stepstuck.html The DRV8825 has a minimum on-time of 3.75μs with an effective off-time of around 30μs (Itby KSevcik - RAMPS Electronics
SDP-SI is a good USA source for small Inch/Metric drive parts. They don't have any exact matches, but there may be something you can make work: "A 6M35M012DF1005" T5 pulley, 12 tooth, 5mm bore, 10mm wide, plastic "A 6A35M010DF1004" T5 pulley, 10 tooth, 4mm bore, 10mm wide, aluminum "A 6Z 3M10DF09505" XL pulley, 10 tooth, 5mm bore, 9.5mm wide, plastic w aluminum insert I'm seriby KSevcik - General Mendel Topics
Soon to be new reprapper, and I'm already hunting down useful mods and such to make when I pull a Ship of Theseus on my Clonedel parts. This is now on my list of absolutely brilliant mods to make. You've done even better than just reducing backlash and increasing accuracy with this mod. By adding a 2:1 gear ratio between the motor and the load, you've actually reduced the reflected inertia ofby KSevcik - Developers