I am starting to build my first Prusa and was hoping that I could get some help with a few issues that I am having:

1. My motors produce a high pitched whining sound when power is applied to the electronics.
2. One of my motors is not stepping properly, it will go in the correct direction, reverse, and then continue in the correct direction. Sometimes this cycle repeats.

I hope that you can understand what I am asking here. If you need more information please let me know.

Thank you,
Jim

Hi Jim. This task may be easier to solve in the IRC forums where we can have you try somethings, and get instant feedback. You can find the link to IRC in the RepRap wiki.

In the meantime, here are some things to check.

1. Are the motors hot, warm, or cool to the touch. By hot, I mean you cannot hold you finger to it for 3-5 seconds without pain. Cool means body temperature. Warm is somewhere between the two (heat but not pain).

Too hot, and it is likely that the stepper drivers have the motor current adjusted too high. If you are using RAMPS or other Pololu-based motion controllers, then there is a very small potentiometer that has a Phillips head. This is the current adj. control. It only turns about 270 deg. from about 7:00 (lowest) clock-wise to 5:00 (highest, don't go there).

The "screw" has a flat spot on the side, this is where you get the 7 o'clock - 5o'clock positioning. Ideally, it should be somewhere between 9:00 and 11:00 clock-wise. In this setting the motor may be slightly warm, or hot to the touch.

2. You need heat sinks and a fan blowing on the stepper drivers. Again, I'm speaking under the assumption the you are using RAMPS. You won't get far without active cooling, so just do it.

3. If everything seems fine considering everything I mentioned above, it could be that you have one wire loose or that you need to flip on motor pair. Stepper motor wires are A+/A- B+/B-, but sometimes, just as common, they need to be A+/A- B-/B+. Flipping one pair in the connector end will solve the problem if this is the case.

Quote

Ideally, it should be somewhere between 9:00 and 11:00 clock-wise. [...] You won't get far without active cooling, so just do it.

I prefer to adjust stepper drivers not by fixed trimpot positions, but by tourque requirements. The absolute position of the trimpot heavily depends on the type of motor you have.

To calibrate the trimpot, turn it all down to the left, then go to the right in small steps until motors runs without step losses. Then add another 10% safety margin to the right. Firmwares with acceleration allow higher speeds as well as lower motor currents.

My Pololus work fine even without a heatsink, much less active cooling, as I have low acceleration. You recognize overheating by motor dropout for about half second intervals. Pololus survive that, so you can always crank up your cooling as needed.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Quote
jcabrer
2. You need heat sinks and a fan blowing on the stepper drivers. Again, I'm speaking under the assumption the you are using RAMPS. You won't get far without active cooling, so just do it.

I've been running my Mendel since December without a fan on the stepper drivers (Gen 3 until Jun and RAMPS since then). For the last month, I've been running it inside a box that reaches 45-50C when closed without a fan and no failure yet.

I think that the need for active cooling on the steppers depends greatly on the type of steppers. I have 2 different types. The smaller ones actually produce more torque but heat up quickly. The larger one appears to work fine without active cooling but did not have enough torque for the wades extruder.

Thank you all for the helpful comments.

The motors are running very hot. I'll try and make the adjustments suggested and post my results.

Jim

I used traumflags method to calibrate my lolus
I burned one up in an unrelated incident and got one without a sink.
I thought hey let try it with out to see how hot the chip was before during and after.
Well it got warm about ten minutes in and never got hotter,
Print finished, temp still not hot.
It all come down to how its all calibrated, and what motors your running.
-E