Lowrider V2 Upgrade (V2.5???)

Test cut tonight…

Drop in replacement for XZ (but belt attachment points are tight unless I redo the router plate).

(and I don’t have the cable angle placed yet).

The ubolt nuts aren’t in the right place (I don’t want/need to mess with the McMaster model just yet).

I think this plus the jig I posted earlier would require minimal alignment (assuming you cut this straight…).

Let me know what you think. Jeb

If you get it working well I would be very interested in getting those plans/DXFs. It looks to be a very good idea.

One problem I see is you’ve got a cutout for the thickness of the material and that’s never consistent and it’s hard to get the perfect fit.

I think Ryan might have been shooting for more printed parts than flat parts because the cnc is more work to operate. But I’m all for other designs.

I came up with this after the test alignment jig the other night. It was such a good fit as I had designed for 1/2" MDF.

And it maintains all centerlines to be a drop in replacement.

For someone just starting a build, if you had those precut and that leveling jig, your machine would be pretty close to perfect from the get go. (As I learned on 3d printing and the lowrider, alignment is everything)

Either way, it’ll be a fun experiment…

Agreed.

Fits like a glove!

And perfectly square!!!

(Although I did assemble one plate backwards – the centerline should be touching the pipe to help grab it).

It took some gentle hammering, but the fit is nice, tight, and perfect.

Cutting the other one now (and I might just cut an one more so I don’t have to flip that plate).

McMaster ubolts are in and fit, so I’ll assemble this weekend if I get a chance.

(and the c/c of horizontal tubing is 126mm right on the money)

Works awesome! Only complaint is the X zip ties, but I think I have a fix.

I aligned with the jig I posted earlier (perfect fit in the dips). Sides are square and it is very strong.

Jeffeb3 – I’m using this as a STARTUP.gcode to lock all the motors:

G90 G21 ; Disable motor timeout M84 S0 ; Zero all axis G92 X0 Y0 Z0 ; input to proceed M0 Enter for Z+20mm G0 Z20 F300 M0 Enter for XY+20mm G0 X20 Y20 F1200 M117 Job end

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I don't know if I missed something, but I'm wondering what the purpose of this change is for? What are you trying to accomplish?

 

Thanks!

It’s stiffer for my large format table. The tubing is locked (and parallel/perpendicular) in all directions.

(and I was having trouble getting everything aligned – I probably had some screws too tight…)

The moment connections at the end (compared to a simple span) reduce deflections.

But the comments are right that accounting for wood thickness in the slots is more difficult to design and cut.

 

Now if I could get a perfectly straight piece of tubing, it would be, well … perfect.

 

Next on my list to finish this is up is:

  • Modify the Y plate so that the belt runs inside the unistrut.
  • Modify the Skate wheel STL so that I can put a bearing on the unistrut edge (I think I just need a vertical hole for a bolt).
  • See if I can belt the Z leadscrews together to keep them locked in sync (see calcs below).
For a 4x8 bed, we should have a Z belt movement of +/- 600mm (about 1/2 the width). Therefore up/down movement (with 16T) would be 600mm/(16T/rev*2mm) * 8mm/rev = +/- 150mm.
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The drivers are moving the steppers in lockstep. That should be more in sync than a 1.5m belt.

Wow, that’s a lot of extra mass you have to move around.

Then do I have a something setup wrong? I’ve had issues with my far Z stepper. When I was just messing around with higher speeds, the closer one could keep up, but the far one lost steps.

And Sunday, after I cut a 4’x4’ pattern, I needed to widen a pocket. I checked my Z0 at X0 and Y0 (returned to X0 Y0 Z10 after the cuts), but the slot on the far side cut maybe 1mm deeper than it had before (and I checked the gcode). Z movements were a max of 150mm/min.

I would keep both Z motors, but also belt them…

But I’m open to suggestions. Change to parallel wiring? Increase Z current from 900ma for series?

As far as mass goes, it seems to be fine (esp. after Ryan’s weight lifting video), the Y movement is great, and I was having far Z hiccups before the new XZ plates.

Thanks for the help.

 

I was having the same issues even with the stock frame. I had to turn up the power of the steppers do not have them miss steps. I have a large frame also an inch over full sheet in both directions. I have had to turn up both x/y and z. I think Z is at 1100 and don't have issues anymore there. x/y are at 1400 at the moment as I am doing a lot of large cuts and could only bring cut speeds to reasonable to be worth it that way. Granted I am pushing the gantry like crazy. For what I need, I need to stiffen up the gantry so am interested in your work as well.

I am using unistrut rails. It would be handy to have the belts run in the strut for me, as for such a large table, I can’t reach into the table in some instances without hitting the belts and while it’s running i’d rather not.

For me some kind of bearing support for the X axis has been on my mind. And one of the higher priority to explore for me I think. I was wondering if using the idea of using the steel tubes for rails on the Y axis like this: https://www.thingiverse.com/thing:2368805 would work. Can be fine tuned along the length. However, a set of bearings that could be run against the unistrut edge I think would be helpful and would be a lot less work.

However, as jeffeb3 said, I don’t think there is any point in tying the Z axis on each side of the gantry together, should not be an issue if things are set up right.

I will try the larger motor currents – thanks for sharing yours.

And thanks for the link to that other design. I need to mod my firmware to add those Gcodes (and take XY homing off the menu…).

That other design does have a stiffer design at the ends of the gantry, but the belts still run on top of the tubing (and that’s some long tubes to source).

I think we’d be better off with:

  • Belt in unistrut.
  • Bearing on unistrut side.
  • Locked gantry connection (see notes below on where I'm at).
Problems with my current design:
  • Table needs to be wider than Ryan's recommended (which I built first).
  • I will keep trying to fix this.
  • Can't put cable angle where it was (the tubing goes up higher).
  • I moved that up higher, but it hits the router cord (so I have to put the dewalt in 180 degrees).
Proposed fixes:
  • If I modify the Y plate to get the belt in the unistrut, I might as well make it longer as well. We have the room with 10' unistrut, and it would fix the angle for the cable. Basically the gantry tubing would space out a little. But I haven't thought this through just yet.
  • For table width, redesign plates to grab from exterior. This would put the Z motor hanging out in space a bit, so it would need a brace. (The extra width between tubing would help for this).
If you are on Fusion360, I can share the in progress files... Jeb

You shouldn’t be skipping steps. The current can be adjusted, but it depends mostly on the ratings of your motors and a bit on how much cooling you have on the drivers. Keeping things lubed and light helps, but it has so much torque.

The thing that isn’t super obvious is that high speed in the Z really invites skipped steps. Those steppers are turning the screws and if you look at the steps/mm, they are 4x more than the steps/mm of X and Y. So asking 15mm/s in Z is like asking for 60mm/s in X or Y. Ideally they are treated much differently. In your CAM or firmware, you can have your max X,Y speeds and accelerations be pretty high compared to the speeds of Z. Steppers moving fast are trouble for multiple reasons. The torque per step is lower, the microconroller has an increased CPU load, and the forces are higher. 3D carving can be a real PITA with a slow Z, but I’m guessing you’re not carving 4’x4’. So you should probably try to keep Z under 10mm/s, and even 8mm/s can be a lot better. If it’s spending too much time in Z, try to do fewer passes, deeper and slower in XY, which will reduce the amount of Z needed, and you can also try a smaller clearance plane value, which will make it climb less.

Series is better than parallel w.r.t. skipped steps.

Rarely, someone has a loose wire connection on a motor and that can cause symptoms like this. It’s hard to diagnose though.

IIRC, Ryan’s rule of thumb on the current is to set it to about 80% of your stepper motor’s rating. If it’s over about 900mA, or so, I make sure there’s a fan on the drivers. Drivers have a max rating too, but it’s usually higher than the steppers.

I’ve not had issues bumping the belts, sure it will move the gantry, but the belt only moves half an inch, that will be barely noticeable at the bit. You’re going to need to slow the z down. Even a stock z while 3d carving needs to slow down a bit from my experence.

I am using the kit from Ryan with the mini-rambo. (All that was in stock at the time, wish I could have gotten the regular rambo). At the default settings, I found the Z to have very little torque. (defaults in the firmware I got were set to 900). I can easily overpower both steppers on Z with just a thumb and forefinger. I had lots of skipped steps even without the router in the gantry and slow speeds as recommended by ryan. I have played with CNC.js a bit, and it is not following max speeds somehow, and with the holding power turned up and the switch to 24v power supply the torque is WAY more now. So when cnc.js moved the z axis really quickly (which I don’t want) it did’nt skip then. Of course I don’t want to overdrive things. There are no heatsinks on the board or a fan with the case supplied.

I have been using linuxCNC with a friends tormach mill and much prefer it, so I plan to replace the board altogether with separate drivers and linuxcnc (probably MESA 5i25 as well eventually) so I don’t want to invest too much more time in the existing setup. But I do want to stiffen up the gantry.

Have you tried loosening the Z tension bolts, and the other build tips (loosen the T8 nut, lube, etc)?

Either board can easily overpower the steppers I have. I ship them set fairly low, but there is plenty of room to turn them up. Very few people actually have this issue though. A screw has a tremendous mechanical advantage. A little force goes a long way. If you think you need more power turn up the drivers from the LCD screen and/or lower the Z axis acceleration a bit. Just make sure they do not get hot enough to melt the mounts.

The current firmware is by default a little higher I believe but the next firmware will have a lower Z acceleration. On the lowrider you can usually tell if you are going to have issues, if the Z falls under its own weight when not powered you are probably fine, if it stays up it is more stiff than most.

So how’s it working out? How did you attach the x gt2 belt?