All Stepper Motors Jump after Homing

I've notived that all my stepper motors jump the first time I try to move any axis, or the extruder, after homing.
I'm using standard Mendel90 dibond kit hardware, with Pronterface.
It does seem to track the position, so It do lose my offsets.

Anyone else seen this, or have an idea.
All step motor wires are tightly twisted per nophead's instructions.

Otherwise, everything is working quite nicely.

Thanks,
Wozzy

http://mendel90.blogspot.com/2013/04/im-starting-this-blog-to-document.html

The first time you move any axis they all jump because the stepper drivers are not enabled until one needs to move. After homing though they should all be enabled so I don't understand what is happening.

---

[www.hydraraptor.blogspot.com]

Thanks,

I'll double check it when I get home tonight, but I'm pretty sure that it's behaving as I described.

By the way: I'm having great fun with the Mendel90, Beautiful design and kit build experience couldn't have been better.

I verified that the jump in all motors occurs after home-all on pronterface. Aqlso the first axis to move seems to move a fixed amount (about 5 degrees) and speed, regardless of the command.

Weird, I can't explain that.

I wonder if the PSU is doing something odd as that is the only thing different from the standard kit.

---

[www.hydraraptor.blogspot.com]

The Z move after home is caused by Z soft limit being lower than home position.
After first move the target position is clipped to soft limits so Z must move back a bit.

ledvinap,

That's a great observation, that makes a lot of sense.
I'll see if I can modify the soft limit, or move the limit switch slightly.
Thanks for the response.

--Wozzy

Wozzy,
The jump is actually the correct behaviour I just hadn't noticed it before because I home with the green HOME button I added, which moves to XY = 0,0. In start.gcode I do the same.The origin is in the middle of the bed, not at the limit switches.

The limit switches are all 1mm outside the print area so they don't get activated during printing.

I don't get the first movement truncated though. If I click home all and then X + 100 it goes 100mm and Z and Y go 1mm.

---

[www.hydraraptor.blogspot.com]

If X and Y limits are 1mm outside of soft limits in firmware (I use same position in my version), then it explains perfectly described behavior.