SOLVED - FullStep Resolution Error

Hello there,

I'm currently putting together a Prusa i3 to be used as a positioning stage (basically I'm going to be putting an ultrasound transducer where the extruder nozzle would go). I'm using ramps 1.4 with sprinter firmware and pronterface to control the unit.

When I try to make the unit move by less than 0.85mm in the X or Y it simply won't move and instead waits until the total movement distance is >0.85mm. It then moves the required distance. The scaling works well for large moves but I just can't get it to make the fine moves I'd expect. I'm using full stepping but I should be able to get single step movements around 0.15mm.

Any ideas?

I've updated the code in sprinter for the line:
#define _AXIS_STEP_PER_UNIT {200/2.5/12, 200/2.5/12, 200/0.8,700}
200 steps / revolution with a 12 toothed pulley with a pitch of 2.5mm (full stepping for now).
and I've updated the pins.h file for use with ramps 1.4

I know that I can turn microstepping on to improve the resolution a bit, but I'd like to figure out why I can only get it to move in increments of several steps as I'll need every step I can get in the final application.

Cheers,

Andre

Edited 1 time(s). Last edit at 04/13/2014 01:37PM by AndreBez1.

Hello,

I've spent the morning getting my head around the code and I was able to figure out the issue. I'm going to post my solution here in the hopes of possibly helping someone else out.

In line 208 of the configuration.h file there is the line (I think this shows up in marlin as well as sprinter):

const int dropsegments=5; //everything with less than this number of steps will be ignored as move and joined with the next movement

By setting this value to 0, I was able to get the printer to move in single step increments. Though this isn't a big deal when using the reprap for printing with high levels of microstepping it turned out to be a problem for me as I was using the setup as a positioning stage for an ultrasound system and needed the finest control possible. Simply put this modification allows single step resolution in fullstep mode. Hopefully in the next day or two I'll have some data on the microstepping resolution and how this effects it.

PS - Sorry to anyone who might find this obvious, but I didn't find many posts referencing the issue so I thought I'd do my best to lay out what I'd figured out.