Wrong stepper motors?

When I purchased my components back in March, the bundles were all sold out except for the 3D printed connectors. I snapped those up, but had to purchase a lot of the remaining components a la carte. From V1, I acquired the RAMBo 1.4; LCD screen; series wiring kit; 12V power supply and lead screw with brass nut. I had to source the NEMA 17 steppers, bearings, pulleys, couplers, and belts elsewhere. Fortunately, the Bundle Contents page on V1 described the components I would need. Some parts ended up shipping from China, so it has taken several weeks to get up and running.

My crown test was successful, but now when I add the Dewalt 611 to the carrier, the Z-axis stepper furthest from the control board is not able to lift it. I’ve examined and adjusted the gantry components until that sucker slides up and down like a baby’s you-know-what, so I’m convinced my problem is not related to a bind somewhere in my apparatus. At this point, I’ve exhausted all my “what-if-I’s”. The motor closest to the control board is able to lift the Dewalt, but when I swap the stepper motor out to the other end of gantry, it can longer muster the strength to lift the router. I was thinking there must be enough voltage drop over the 58" distance to cause the far motor to starve for electricity(?). I’m using the straight extension wire from the series wiring kit to connect that far stepper to the control board. I purchased my steppers from Amazon using the following link:


which appears to correspond to the specifications of the stepper motors available from the V1 web site. I would think they should be powerful enough to do the job, unless I’m fighting some electrical issue that is beyond my basic understanding.

I’m attaching photos to supplement my descriptions of what troubleshooting I have done so far.

Loosened all bolts & nuts enough that I can turn them quite easily by hand. I’ve verified the Z-axis tubes are against the little ridge at the top of the end pieces. I can rotate the Z-axis tubes easily by hand and can even get the X-axis tubes to move, as well. I removed the upper gantry and adjusted the end piece bolts so that the Z-axis tubes are parallel to their partner, recognizing that the gap in between the end pieces should be uniform. I did not use a feeler gauge because I felt that parallel axes were the determining factor, here. When I put the upper portion into the lower half, everything dropped into place with no resistance. The lead screws barely stay within the brass nut long enough to get the coupler attached; they rotate back down on their own. Brass nut is kept fairly loose on the Y-axis motor mount. The gantry drops back onto the Y-axis section under it’s own weight. I can raise the gantry using one hand to turn the lead screw. I replaced the aluminum couplers because, to me, they looked like they had stretched somewhat in my photos. I marked the lead screw with a Sharpie so when I reassembled the coupler, I could easily find the position as described in the instructions (not past the top of the bottom collar). The coupler was slid onto the motor shaft until the shaft made contact with the lead screw. I tightened the coupler grub screw onto the flat of the shaft before tightening the second screw. I lubricated the lead screws using the cycle chain lubricant shown in the photo. Verified the Z-axis tubes are not rubbing against the sides of the table.

In addition to physically swapping the two Z-stepper motors, I’ve swapped the connectors on the control board. I use the LCD to raise the gantry by 1mm increments. Sometimes the far motor will immediately stop rotating and skip steps - other times, I might get it to raise up to 5mm before it malfunctions. Without the router in place, the gantry will raise and lower without a problem …even when I use the LCD 10mm increment option.

Unique things I have done on my build are as follows:

I cut the flat pieces with hand power tools using a template found on the web site. All screw holes were initially pierced with an awl to eliminate drill bit walk. Some edges had to be rasped so the components could tuck into openings and abut against the flat piece without restriction.

Initially, when assembling the Y-stepper mounts, I had difficulty manually turning the lead screw and raising the Z-axes. I noticed the coupler was being tilted. To alleviate the bind, I had to recess the hole for the Y-stepper mount by 1/8". The lead screw turned like a dream and everything was sliding up and down and behaving itself.

My build is maxed out so can cut full 4’X8’ sheets of XPS foam. Therefore, to reach the far Y-stepper motor, I had to splice more wire into two of the series connectors from the wiring kit. I also had to configure the third series wire from the wiring kit so I could reach the X-axis motor when it travels to the far side of the table. Both X and Y movements work very well.

I have a feeling I’m missing something very obvious on that Z-axis, so I’m hoping someone can knock me up 'long side the head and get me back on track.

I like that creative use of straws. I’ve never seen that before.

I think your hunch might be correct, that something is causing the far z-motor to ‘starve’ for electricity. The dual connectors on the RAMBo essentially create parallel wiring of the Z motors, which cuts the current through each motor in half. This is if they are equally balanced in resistance, but if one motor has higher resistance, then it will get even less than half the current (and the other motor will get more than half). It seems unlikely that the resistance of the wire would cause this difference, but perhaps the connectors could add some resistance. Note this is not because the connectors are “bad” per se, but simply because the current prefers to follow the lower resistance path, which causes ‘starving’ for current.

Try using series wiring on the Z motors instead. Use only one of the Z ports on the board and use the series wiring harness. At a minimum this will double the current through both motors. Both will be getting full current, and if the far motor was getting less than half the current due to imbalance of the resistance, it will see a big improvement.

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Winner, winner, chicken dinner! That was it! I stole the cable from the Y-steppers, since that was already wired in series, to test the Z-steppers and they work at full LCD speed with the router in place and vacuum hose attached. Thank you very much! I believe I’m ready to go…as soon as I create a new series cable to get the Y-steppers up and going, too.

My wife teased me about the diagonally-cut drinking straws, also. But it kept the wires under control until I found some real cable wrap.

Much obliged!