It has some simple pen springs in them. They work well for the pens, but probably do need tighter ones for the chalk

I had thought about the chalk paint since another design on here had used it, but after looking at the one at Lowes online, seemed like it might be difficult to wash off. That one looks like it should wash off, so I will look into that further. Just have to figure out how to mount it with a servo trigger. Thanks for giving me another source to look at.

Meanwhile, I am revisiting the Wheel plate design. I used the pitch angle for the HTD5 belt for measuring the belt connections but seems like it is looser than it should be. This image has the top idler pulley at its upper most adjustment. It was sized for the belt to perfect length at middle spot (3mm adjustment on each side of center) Maybe these were measured by inside diameter.

This design change should beef up the support around top idler. I also moved the idler pulley up 3mm which should be enough for tighter belt. I am going to print with 6 Perimeters & 70% infill this time & use PETG. I was using PLA+ with 5 Perimeters & 40% before.

 

One of these 3 designs might be a good starting point for the spray can trigger.
Spray Can Handle to end them all by Kaishou
Printables
or this one that has the servo in the design
Printables

 

I redid this design with idler pulley below motor & GT2 drive belt length changed from 220mm to 240mm. Did not seem as accurate as previous version even after slowing it down quite a bit. This idler uses 625 2RS bearings with M5x50mm screw whereas the previous idler bearing with the teeth used 608 bearings. I think the thinner M5 screws & associated bearings are probably the weakest link here. Here is a photo of that design change.

I am going to try yet another design idea, using the motor to drive that HTD5 belt around both wheels. I did something similar with original design, but that used o-rings for the tires. I have the parts all drawn up & will print & see how this works. I am printing 20T HTD5 drive pulley 1st as that is the shortest print before printing the other parts. Seems like I have enough teeth on the 20T drive pulley engaged to not need an idler pulley. These teeth are a lot deeper than the GT2 belt & there are 4.3 teeth engaged at any time.

 

You might be on to something there with the weight distribution. Test run today with idler bearing below motor shows the wheel side with the above motor being more askew even after slowing it down to 2400mm/Min from the 6000 tested with other design. To even out the weight, I could move that motor to running with the carriage similar to how my cantilever laser design works with the carriage on the 2040. Would have to change it a bit to work with this design and electronics locations would have to move some. That would also add more moving weight to the carriage.

[Edit] Think I know how to get this motor in the center without getting in the way of the electronics. That should get rid of any balance problems. Thanks, JustinTime for giving me the idea to look at this problem differently. Think it will be something similar to way a Corexy does at the corners with idlers around around it.

Here is what the plate design I tried yesterday & this morning looks like.

Since the design with geared idler above motor worked the best so far, I reworked that design to give it more support around the top idler bearing. That should cut down on possible flex from that connection. Plate is mostly 6mm thick & 12mm thick around that top hole & 17mm thick around wheel bolt holes. For reference this is called 7B design

I also worked up a design to use the HTD5 belt for both the drive & the tire tread. I don't know how well that 3d printed HTD5 20T drive pulley will work, but it does move the wheels closer to the plate and simplifies design. Seems like I might not need an idler pulley with this design since the teeth are bigger & I will have 4.3 teeth engaged with a 20T drive Pulley. Will see how well version 7B above works before deciding whether to print all these parts.

Yet another idea to give it a little more weight and would also help to hide some wiring is to use C-Beam instead of the 2040s. It is a bit extra cost & I only have 1 500mm C-Beam, so would have to buy another one to test it.

If I ever finalize this design, a 1/4" aluminum wheel plate would solve any flex problems or even a 1/8" plate with 3D printed plate behind it.

 

Thanks, I had not thought of moving the battery, but did think about putting each side on a scale. I didn't get around to that because the idea of moving the motor took my attention.

I think this design should balance out the weight distribution. I looked at the Voron coreXY design to see where to put the idlers. I ran out of the F695zz flanged bearings for the idlers, so designed a plastic one to fit in there. It had to be a little wider for the plastic idlers. I am using just one 625 2RS bearing in each idler. I might order some more of those flange bearings but made these in case I needed them. This might be a little tight squeezing in the electronics, so will probably go to 800mm or 1000mm 2040 with 500mm length 2060 in the middle. This motor change also gives about 30mm extra width on the plotter. It looks pretty good on paper.

[Edit] I moved that new motor mount 8mm towards the carriage to make the belt straighter. For reference later, the measurement of the belt in the design for 500mm 2040s is about 1160mm.

 

I have had several false starts with the latest test. The motor wires I was using have Dupont connectors on the board side & kept coming loose in the JST board connectors. I have some motor wires with the 4 pin JST connectors, but they were wired wrong. I was finally able to find the right little screwdriver that allowed me to pull those pins out & put them in the correct plugs. Nothing like a snap fit. Thought I was ready to test again, but servo would not work, so I had to use the spare one I had. I use M2.5 screws to hold it on & those small locknuts were hard to get off the way I had them on & broke the plastic mount in the process of taking the servo off. I did some minor modifications to the part before printing again. Finally had it all back together & ready to print.

I am also modifying the wheels some which might help the accuracy. I had the bearing recesses at 22.5mm with 22mm Outside diameter bearings. I did this to make it easier to get the bearings in & out as I was going thru iterations of the wheels. I had the intent of making them tighter later. Today was the day to modify them. I did a couple of test prints, 1st one at 22.4mm which fit good with no filing & then 22.3mm which fits tight with a couple of minutes of filing. I am going with the 22.3mm for tightest fit.

I adjusted the acceleration down in Klipper from 2000 to 1000 & movement seems smoother. Still does not have as good of accuracy as with the belt idler above the motor. I will redo the wheels & try that again. Here is the video of today’s test.

 

I had a printer jam again yesterday while printing the wheel, so decided to change the wheel design a little more. Seems like one bearing might work just as well on the wheels and maybe even better since I am putting a wider spacer where it connects with the wheel plate. I am going to do the same thing for the idler that is below the motor. This decreased the M8 bolt length from 60mm to 50mm & the M5 idler screw from 50mm to 30mm. I will print the idler pulleys first since they are a lot quicker prints & that should give me an idea of how well this should work. Here is a slanted section cut thru the wheel & idler to show the inner details of my description.

 

I had the same thought about the machine always moving forward with the design & any imperfections would not be noticed especially when dealing with chalk. The repeat on the couple of circles was an accident, but left them in there so I could visually see how far it was off. I am trying to get the accuracy as good as I am able just to see if it could be accurate enough to put a diode laser on it. Add some more weight to it and a wider tread belt & might even be able to put a Dremel type tool on there. I am going to switch to 800mm length 2040s with a 2060x500mm V-slot in the next week or so. 1000mm lengths are little too long for me to easily work with. The extra 300mm length will give me more room to move the electronics around & will still barely fit on the 36"x24" cutting mat.

The single bearing idler flexed too much which is probably because of too much overhang of the tire belt beyond the end of the M5 screw. I will stick with double bearings. If I can get my printer to cooperate, I am going to reprint a stiffer wheel plates with geared idler bearing above the motor. If those work well, I will reprint the wheels with tighter bearing recess tolerance. I do think making the bearing recess holes a tighter fit on the bearing should help at least a little bit.

As to the wider belt idea mentioned earlier, I was considering getting a 25mm wide belt to replace the 15mm belt. Only problem I see with that after seeing the problem with the overhang issue of the single bearing is it might have a similar problem since the wheels will be extended 10mm further out from the plate.

I need to spend some time one of these days seeing if I can get the DLC32 board running FluidNC. I could then take the raspberry Pi out of the mix. I did get the raspberry pi to operate as a hotspot in case I am somewhere outside my Wi-Fi area. It turned out to be fairly easy to do using this tutorial. Raspberry Connect - Raspberry Pi - Auto WiFi Hotspot Switch - Direct Connection

 

Jamie on the V1engineering forum gave me the idea to support the wheels & idlers on the far end. This is what I came up with using that idea. I just finished printing the other plates, so have to test them first before looking further at this idea. This new idea looks to be very promising.

 

I keep some of them from old projects that I might put back together, but old versions that didn't work end up in the trash usually. I don't have a way to recycle them here. I sometimes have a couple of old parts sitting back the couch & I fiddle with while watching the TV. Guess you could call those fidgets especially the ones with bearings or gears on them.

 

I woke with another idea to carry this a little further. Since it is now supported on both sides & 8mm smooth rod is better tolerance fit than the bolts for the bearings, why not change the bolts to smooth rods. That should get rid of any possible wobble in the wheels. Looks like it works on paper. I am using 2 - M3 screws on each side of the main bracket & only 1 - M3 screw on the back plate. Probably only needs 1 - M3 screw on the main bracket also. I still have a couple of minor adjustments to the design before thinking about print it. I would probably keep the idler as a M5 screw. I am starting to see 25mm or 30mm wide HTD5 belt in the future of this.

[Edit] looks like the 8mm rod is too tight a tolerance for the 608-2RS bearings. Thought I had used that before. The 8mm rod will work with LM8UU Linear Bearings, but not sure I want to use those. Any thoughts on this?

 

It is worth considering, but not sure how well that shaft would hold up over time. What do you think of these polymer bearings? I have 4 of these & they feel pretty good on the M8 rod, but not sure how well they would wear overtime. Also not sure how well these would fit into the design as they would not be used the way they normally are.
Amazon.com: 3D Printer Solid Polymer LM8UU Bearing 8mm shaft - Igus Drylin RJ4JP-01-08 for Anet A8 Prusa i3 3D Printer RepRap : Industrial & Scientific

 

Someone on the v1 forum also mentioned that about the LM8UU bearings. You can get these to use instead of the metal LM8UU bearings, but not sure how well they would hold up overtime. Amazon.com: 3D Printer Solid Polymer LM8UU Bearing 8mm shaft - Igus Drylin RJ4JP-01-08 for Anet A8 Prusa i3 3D Printer RepRap : Industrial & Scientific Here is section view of the wheel I drew up using these. I have one of these 8mm lock collars from openbuilds Lock Collar - OpenBuilds Part Store drawn at top of wheel to hold the bearing in on that end. Looks like this would work, but would have to reprint the wheels which I am not inclined to do just yet.

Someone on the V1 forum also mentioned using a slotted pin similar to a roll pin for the shaft. I drew this up to see how it looked, putting a bolt head on one end & would hold it with a real or plastic nut on the other end. I will see how well the real bolts work first since I have some.

I started thinking about the idler pulley for the HTD5 belt that is currently using the M5x60mm screws. I wanted to use the same 608-2RS bearings for this but didn’t have enough room for a housing for the bearings. I then realized why do I need a housing for them. The belt is constrained with the wheels & shouldn’t really need it. If I did, could always add some sort of fender washer. This would also make it easier to source the hardware as 5/16" is a good substitute for M8, but I don’t see a good substitute for M5. It is also easier to find longer M8 than M5 hardware. If I end up going to 25mm wide belts, those bolt lengths would probably go to 70mm. I bolted a few of these bearings tight together with a M8 bolt and they move well. I will probably end up ordering some 25mm width HTD5 belt soon but will see how well the 15mm wide belt works first. It seems more difficult to find 30mm width HTD5 belt. Here is what I had in mind for those 608-2RS bearings & it does look like it fits without hitting the inner drive belt with lots of room to spare.

 

My M5 hardware will not be here until later today, so I went to ACE hardware to get some 3/16"x2.5" screws since they are not too far off M5 (4.76mm) & they ended up being #10 which is the same as 3/16". I was initially thinking #12 were the same as 3/16" & figured since this is on the idler & the belt is pulling up, a smaller diameter probably doesn’t matter for this use. Of course, #10 is the same as 3/16", so it didn’t make much difference with the M5. In putting it together, I needed to rotate the 20T drive pulley around in the motor. I had it rotated with grub screws to the outside before. When I reprint the tires for 25mm wide belt, I will move that tread another 2mm out to make sure it clears ok. The motor wheel plate I printed 6mm thick & the outside plate 4mm thick. I was thinking I could go a little less than that but seems like motor plate needs to be 6mm thick. It was initially a little tricky getting that tire belt on there but putting free wheel on last makes it a lot easier. I have to reprint the idler pulley with limit switch on it where it connects on top of V-Slot before I can test this. Those wheels do not flex at all thanks to Jamie on the V1 forum for that idea. Here is photo of it together.

 

Definitely rolls better, but accuracy is still not where I wanted it. I ordered some 25mm wide belt today after redesigning the parts to fit the wider belt. That will take 2 weeks to get here, so might try playing with some other settings in the meanwhile. Tighter fit on the wheel bearings might help some more.

[Edit] Just realized I have the HTD5 tire belt tensioned from the bottom instead of from the top. I was wondering why it was close to the motor pulley. Just got my M5 hardware, so will swap it around when changing that.

 

I have the C-Beam configuration to test now. I had a little bit of a problem to overcome before putting this together. A couple of the holes on the C-Beam were over 1mm off center, so OpenBuilds sent me a replacement. Unfortunately, the replacement had the same problem. Is 1mm off within tolerance? At this point, I just decided to change the design to have slotted holes for these and did a couple of test prints to make sure they would work. I also decided to change the design to be able to connect on the Sides of the C-Beam. This is probably a simpler connection anyway since no holes need to be tapped, just 8 more T-Nuts needed.

I tested the new wider wheels (25mm HTD5 belts) and it seemed to be a little more accurate but was still visually off parallel to the cutting board lines after the test run. I didn't put a pen on there or run a video of it. The weight difference between each end was only 1oz. I don't think that is enough weight to try & compensate for as that will change with the gantry going back & forth.

Late yesterday, I changed it from the 2040s to the C-Beam. I am using a 2060x250mm for top and bottom which gives me a hidden channel to put some ballast in if needed. I used this gantry for the C-Beam V-Slot Gantry Plate - Universal - OpenBuilds Part Store. I drilled a 1/8" (3.175mm) hole at the top on each side where I add the belt clamp parts. That change, a longer V-Slot 2020 & adding a longer 3d printed shim plate was all I needed to use this. I do loose a little more width since this plate is wider. Think it is about 10.5", but I might could adjust the design a little to get a little more width if this works. The wheels hit the bottom inside plate where the T-nuts are connected underneath. I could use drop-in T-nuts there to gain a little space which would allow me to shorten part underneath. I might could even do away with the T-Nuts on the outside underneath. I could also just cut myself a plate that is narrower since it does not need to be this wide for this application. I will see how this works before making any more changes. With the C-Beam configuration, the machine is 3.5lbs heavier. My thought is the extra weight might help with giving it more traction. I will test it sometime today.

 

I thought about that, but the z-axis 2020 connects on that screw hole. I might test that if it comes to that, but not sure I have enough room for low-profile screw between the Plate & C-Beam. There is one set of holes that lines up on the bottom V opening of the C-Beam, so might be possible.

 

The C-Beam version was actually a lot further off. Since the wheel plates on each side are a subassembly and did not change between the 2040 & C-Beam, seems like the extra weight should be the problem here. I am using TMC2208 steppers & have the Vref set to 0.45v on the 0,0 wheel side & 0.47v on the far side. Does someone have a recommended voltage for this? I am thinking of going to 0.65v at least & retesting. Might not be able to test it until Monday.

[Edit] I pulled the driver chips off to verify the resistor size & dipswitch settings for the microstepping. They are actually Bigtreetech LV8729 chips capable of 1/128 stepping. I have them set to 1/32 with the board jumpers which I seem to now recall doing to match the DRV8825s that I had on prior to these. The VREF formula bigtreetech shows for these is I= Vref/(Rs*5), Rs=0.22Ohm, Imax=1.8A

Vref Amp
0.45 0.41
0.65 0.59
0.75 0.68
0.85 0.77
0.95 0.86
1.1 1
In klipper config I have
microsteps: 16
rotation_distance: 23.8
Be to be consistent, I should change the microsteps to 32 & adjust the rotation_distance accordingly.

 

I never got the accuracy I was looking for to be able to use a laser but was considering it and a little Dremel type tool. I do have one other change to the latest wheels to try, but have not gotten around to testing them, mostly because I need to file the bearing slots quite a bit on them. You might want to read this other thread on my design, starting in the middle about here. Rolling Plotter build - Random or Off Topic - V1 Engineering Forum dkj4linux put a laser on it, but he had to constrain the wheel movements to get the accuracy needed. Using a laser in an apartment sounds a little dangerous especially around kids. Make sure you use adequate protection around it if you use a laser.