3D printed 1/16 scaled RC rotating tracked dumper

Have any of you have been following Designs in Orbit's video series Rebuilding the Clinchfield?  They've been documenting the rebuilding of the 40+ miles of CSX railroad tracks that were destroyed by the hurricane Helene flooding.  If you've been following it then you've seen the little-ish rotating tracked dumpers in action.  They caught my eye, and unfortunately they were bright and shiny enough to catch the attention of my project Muse too.  Ever since that happened I've been nagged at that "WE" needed to 3D model one to build an RC model.  The majority to the tracked dumpers in the videos are Terramac RT14R's.  I said they were little-ish, they're only about  by 20' long by 10' wide - but they've got a 28,000 pound payload capacity. 

After being nagged by the Muse for several months, I finally broke down and started to work on the 3D model.  I found a 3-view drawing on Terramac's website, scaled it to 1/16 because that's the scale the rest of the fleet is going to be, and started drawing it out.  I had it in the back of my head that I could save myself a LOT of time and trouble if I could use off the shelf tracks - like Bruder's replacement tracks for their CAT excavator.  I'd been working on the frame for several hours when I finally got around to checking the scale track width, it was over 60mm.  Well, that's that, this project's over.  I told the Muse that this project wasn't going to happen, 40mm tracks on a machine meant to have 66mm tracks would just look ODD.  Then the Muse started crying and whining that it'd seen an RT7R on Terramac's website, and it was pretty sure it'd seen at LEAST one of them in the videos - what about a 7R?  So, I downloaded the 3-view drawings, scaled it to 1/16, and checked the track width.  Son-of-a.... 43mm.  Well that's close enough to 40mm that it wouldn't be noticeable, I guess we're doing this thing.

For those of you that are curious, this is what a Terramac RT7R looks like.

Cute little buggers aren't they? 

Well the Muse has been cracking the whip for the last 4-5 weeks, and this was the state of the 3D model a couple days ago.

It shows the engine bay door open because that's where the main power switch and the cooling fan are going to live.  The rest of the really important stuff like batteries, receiver, and the ESC's for all the motors are going to live in the rest of the engine bay and in the area for the fuel/hydraulic oil tanks that's just in front of the engine bay.  I was worried about the slew ring and the slew bearing, then I stumbled across across an Ebay listing for NOS Kaydon and Fafnir slim-line ball bearings, when I found out it had what I was looking for I couldn't hit the "Buy It Now" button fast enough.  I figured out a way to 3D print the slew gear using the profiles for a 6mm GT2 timing belt, like the belts used in 3D printers.

I barely had the cab finished before my operator was demanding that I print out the seat, so he could see how well it would fit his butt.  I did, and he did.  When I asked how it fit, I was told in no uncertain terms that the seat back needs to be tilted back, the headrest needs to be tilted forward, the armrests need to be lengthened because the joy-stick locations are under his wrist - NOT in the center of his grip, and that the top 1/3 of the headrest needs to be lopped off - because it just looks stupid.


Sooo.... I fixed all the items on the operator's punch list, heck I even gave him joy-sticks - with cushioned grips.  There shouldn't have been any complaints - but... there were.

The operator was whining that it was a little snug on his hips.  I told him he had 2 options, deal with it - or diet.  The other guy was so PO'd that he only got the "reject" chair to sit in that he said he was gonna hold his breath until he turned blue.  So far he's managed to turn his clothes a lovely shade of blue, does that count?

Next up on the hit parade?  Finish up the clean-up work on the cab and bed, then start printing the yellow parts.

Don

This is looking like a fun project for sure. What size of a build plate is going to be required?

Oh, and I'd tell the whiny guy to make his own seat!



Tom

Looks like a great project! Got the popcorn ready. Re the seat - maybe make one with projections upward like little traffic cones, and ask Tim and Terry Mack the operators which they liked better...

Great that you found a Bruder track that was close enough. You're right, that will save a pile of time.

Very cool!  I've never seen a dumper that rotated like that, should be fun! You can get slip rings to take the wires down through the slew ring and let it rotate without winding up the wires. 

wagnmkr - My go-to printer is a Wanhao D6 clone with a 200 x 200 build plate.  I may have to get a little creative, but everything should fit on that build plate.

cnr6400 - I got the idea of using the Bruder tracks many years ago.  They were building a new electrical sub-station and upgrading the power lines along the route I used to commute to work, and they were using a Morooka 1500 non-rotating dumper on that project.  I started to design a model using the Bruder replacement tracks and parts cut from 1/8" and 1/4" plywood on my CNC router.  Then that router died and life got in the way so I never finished it.  My project Muse has been hinting that we need to revisit BOTH of those projects.

crueby - My 6 channel 2A slip-rings showed up 2 days ago.  I would have preferred something with a little higher ampacity, but my main drive gearmotors stall current is supposedly 1.8A - so the 2A slip-rings SHOULD be OK.  The main drive motors are the only thing on the main frame that needs juice so I've got 2 spare wires if something goes belly-up in the future.

Well, after 8 different calibration cubes trying to get the scaling values in Prusa Slicer dialed in for the yellow filament I'm using, I've found one thing about their slicer that I don't like.  You can't save the scaling values as a default, every time you add an object to the print bed you have to manually modify the scaling values for that object.  Don't like it, I'll live with it, but I don't have to like it.  About 1/2 hour ago I started the dump bed center section printing, if all goes well by about noon on the 4th I should have a completed print waiting for me.

Don

Fingers crossed all goes well!

Write your complaint on the Prusa Forum Wish-List and it might end up in the program soon if you can get people to see the problem / solution .....

Will follow with interest 

Per   

Before I went to bed on the 3rd I started a print of the center section of the dump bed. it was a 13+ hour print, this is what it looked like at about 11:00 on the 4th.


It failed, for many reasons, but mainly because you can see where it's lifting from the print bed.  I let it finish to see if there would be any more issues.  Then I did a post-mortem on it and found some more boo-boos.

1) I HAD a 1mm x 2mm lip designed into the faces where the center and rear bed sections mate together - that lip's gotta go.  That lip reduced the contact area on the build plate by almost 50%, that's also where the print started lifting from the build plate.  Eliminating the lip, and adding a brim to the print, should eliminate the part lifting from the build plate.  Ditto for the lip on the rear bed section.

2) The 2 line-up pin holes, the holes that run almost the full length of the bottom bed rails,  appeared to be filled solid.  When I checked the slicer it had put support inside the holes, apparently to support the bridging at the top of the holes.  (They're only 2mm holes.)  I can see 3 ways to fix this, one's easy, two aren't.  I'm going to hit the "Easy" button and make them thru holes, I'll plug the open ends later.  Ditto for the rear bed section line-up pin holes.

3) There's boogers and stringing on the bed interior along the length of the top bed rail.  You can sorta see the fuzzies in this picture.

This is probably caused by retraction and nozzle wiping issues.  The crap scrapes off, but if I can fix the issues it's that much less clean-up for me to do.

4) There are several/many areas where the support has bonded too well to the part.

I've seen this before, I'll need to modify the part/support separation distance setting.  I CAN chisel this off, but if I can make the support pop off easier - I'm gonna.

5) Worst of all, the stinkin' scaling is STILL wrong, and each axis is off by different amounts.  I spent a VERY frustrating day trying to get Prusa and my printer to poop out a part with ACCURATE dimensions.  I'm about ready to BRUTE FORCE this issue!  I'll do what I did 10 years ago on my first Chinese clone printer, before I knew about using scaling for shrinkage.  I modified the startup script to change the steps/mm settings in the G code.  Every time I sliced an object, the correction factors were automatically loaded into the G code file.  I only print PLA, so once I get the correction factors dialed in, I can forget about it. (Until I decide to print something other than PLA.)

Don

One thing I had to do on my Prusa printer (now a Mk4S) with large PLA parts was to up the bed temperature to 70 from the default of 60 (in addition to cleaning it well with alcohol when its cold). That got rid of the tendancy for the part to warp halfway up and lift from the bed. Adding a skirt to the settings can help too, increasing the footprint on the bed. For supports, I usually use the 'snug' option with normal supports rather than the organic style - prints lots faster too.
How accurate are you trying to get with the size? I've printed out submarine hulls in sections, and things fit fine, but if everything was off the same amount I wouldn't have noticed.

I also have a Prusa, and have to say I get better results than that.  I use the default options for support and they work pretty well for me. You can usually run an exact knife along those overlap places like you show, and fairly easily wipe away most of that crud.  At least, that's what works for me.

Those 2mm holes won't need any supports. If you can't leave 'supports' off, you can try 'paint on' supports, and only add them where you specifically need them.  Not as easy as 'from buildplate', but it works pretty well and isn't too hard.

Just a few thoughts.  Sorry you're having so much trouble with your Prusa. Which one do you have?  Mine has worked quite well with very little tinkering on my part.  And the dimensions come out spot on. I do print mostly with PLA, though. What are you printing with?

Kim

I spent yesterday working working on getting the thing to print as accurately as possible in X&Y, since they will be the directions that will be the most troublesome.  I went back to using the method I developed 10+ years ago to get my first kit-built printer dialed in.  I use the M92 command and modify the steps/mm settings in the start-up script.  That way the printer gets told the correction values every time a G-code file is loaded, and I don't have to remember to change anything.  I designed a 100mm calibration square that prints in less than 5 minutes, the walls are 2mm wide and it's only 0.6mm thick.  It took me 3 tries to get that square printing to 100mm, +/- 0.05mm.  I called that close enough in X&Y, and printed my 40mm test cube to check Z.  That cube takes about an hour to print.  When it completed X&Y were real close, but Z was about 1mm undersize.  So I gave everything one final tweak and called it close enough.  I then printed the front wall of the dump bed.  It's supposed to measure 135mm x 76.83mm in X,Y.  It's printed dimensions are 135.12mm x 76.99mm - close enough.

Crueby -  I need the parts to be as accurate as possible, I'm not just trying to fit 3D printed parts together.  I've got to get them to fit other parts, like the slew bearing from Fafnir.  I don't mind a little light sanding to get parts to fit, but if a part's supposed to be round - I want it to print ROUND - not oval.  I'm also printing the 60+mm slew gear, which needs to mate up to a store-bought 14T GT2 pulley.  I'm adding a brim to the parts that have a small contact patch with the print bed.  I use the start-up script to print a priming strip along the edge of the build plate, that way I don't need to print a skirt around the part to prime the hot end.

Kim - I don't have a Prusa printer, I have a 5+year old D6 clone from Monoprice, and I am printing in PLA.  I am however, using the latest version of the Prusa slicer though.  I agree a 2mm blind hole SHOULDN'T need support, however...  The dump bed center section needs support at multiple levels while printing, so the "from build-plate" option is the best one.  I just changed the two blind holes into through holes, I'll plug the open ends with filler later.  I've just started using the Prusa slicer, so I'm finding things that need to be tweaked from the default settings.  Like the part to support clearance setting, that setting defaults to 0.2mm.  I had the same problem with the support sticking to the part, where it 's not supposed to be touching, when I used Simplify3D as my slicer.  I changed that setting from 0.2mm to 0.5mm, and the problem went away.

Don

I'm gonna nominate myself for the Bonehead of the Month award. 

I just spent about a hour cleaning up the 2nd attempt at printing the dump bed center section, a print that takes almost 14 hours and uses almost 100g of filament - only to realize that it was too flippin' big!  I spent all day yesterday trying to fix this problem, whaahhoppen? 

I looked at the dimension for the STL file, and it said that dimension was 139mm.  Alibre generates the STL file, so that's where the problem is.  I looked at the 1st sketch in Alibre for this part, because that's where I generate the basic outline for the bed, and it said the bed was supposed to be 135mm wide.  WTF, am I scaling this part?  I thought I took that out already.  When I first started designing this thing I was using Simplify3D as my slicer.  It does strange things to any ID's when it scales a part, so I did the scaling in CAD.  Sure enough, hiding as the 2nd to last item in the design tree was a Scale Part item.

So....  I wasted 28 hours of printer time and over 200g of filament because some doofus forgot to delete a Scale Part item in the design tree.  The good news?  I told the printer to print me a 139.05mm object, and it printed me a 138.97mm object - that's close enough.  And that's the best that I can do to make a silk purse out of this sow's ear.

Don

Can you scale up the rest to match the larger bed, and use the too-large bed?

Crueby - It was simpler just to reprint the center bed section because.....

Houston... We no longer have a problem!

All the parts match the nominal 135mm width.  As I was fitting things together I realized that I didn't include the line-up pin holes in the bottom rail of the rear section, so I'll need to reprint that section.

A few more yellow parts to print, then on to the grey.