3D printed 1/16 scaled RC rotating tracked dumper

Don't feel dumb, they DO clear each other.  The only reason that they clear is because I had to add another 9-10mm in height between the upper and lower frame sections, 9-10mm that shouldn't be there if this beast was true to scale.  I know, I know, it's not that big of a deal - it just bugs me that I can't find a way around it.

I didn't get much done on the RT7R this week.

About 2 weeks ago my Toro Recycler lawn mower decided to go on strike, it ran long enough to mow about 150-200' then died.  It would restart, then die again after a few seconds.  The Toro is a few years old, and this is the third time in 2 years that I've had carb problems, so I decided to order a new one.  While I was at it I went ahead and loaded the parts cannon, new carb, new belts for the AWD that was no longer driving, and a new bag for the bagger - since the original bag had a hole in it.  ALL the parts showed up on Tuesday, and I got busy.  By Wednesday afternoon I was ready to give it a whirl, it mowed about 100' before dying - and refused to restart.  It WOULD start if I gave it a shot of gas in the carb's throat.  I remembered that one of the videos I had watched mentioned that some of the lower priced carbs' had jets that were not working right and figured, "Just my luck, I got one of the duds."  I ordered one of the medium priced carbs and had it overnighted to me.  By late Thursday afternoon I was ready to try again, made it about 100'!!  The original carb failure was a coincidence, the original carb's failure AND a new carb failure was suspicious, but three failures in a row...  That's enemy action, something else was going on here.  By now, it was late Thursday afternoon and I'd had enough of this crap for one day.

Friday morning I started tearing into this to find whatever it was that I was missing, including tearing my brand new carb apart.  When I did that, I found the culprit - I had water in the gas.  This engine has an automatic choke, when the choke was closed it was able do get enough gas to run,  When the choke opened - not so much.  I carefully cleaned the carb, apparently no so carefully as I managed to lose the float needle.  Remember the first new carb I ordered?  It just became the parts donor carb.  I took the jets assembly from the first carb, cleaned it, dried it, and installed it in the second carb, I even installed the carb on the engine.  That's when I noticed that I hadn't put the float, or the needle, back in the carb.  Those just might come in handy.

With everything buttoned back up, I put some FRESH gas in the tank and tried starting the racken-fracken thing.  It started on the second pull, and ran, and ran, and ran.  All the while with me doing the Happy dance.  It is SOOOO nice to have the AWD working again, I didn't even break a sweat until I started mowing on the lee side of the house.

Now maybe I can get back to the important things, like working on the RT7R.

Don

Yesterday I started working on the RT7R again, almost wish I hadn't.  I installed over 2 dozen M3 heat-set threaded inserts, and while I was doing that, I noticed that they were going in AWFULLY easy.  Well...  when I started assembling the parts using those inserts I found out why.  The inserts started pulling out almost as easily.  Remember the issue I had with the bed pieces not printing accurately, effectively printing under-sized?  One of the things I had done to compensate for this was to print any pockets over-sized.  I never even gave this a thought when I printed the frame parts that needed the threaded inserts, so the pockets for the M3 inserts and the magnets were all were all printed too big.  I'm going to have to reprint those frame pieces.  Since I've already glued some of the bogie parts onto the lower frame, I'll need to reprint them too.  I MAY be able to recover some of the inserts, but I'm thinking that reusing them is probably not a good idea.

I've probably got enough grey filament left on the spool to be able to be able to reprint the parts.  But I'm wondering if using that filament is a good idea, as I'm having trouble with it.  It's actually several years old, and if it sits in the printer for more than a day or two, just the stress caused by unwinding the filament from the spool will cause it to break.  The filament will usually break in the feed tube, where the break isn't really visible.

This also happened with the yellow filament when I was printing the bed parts.  What I did then was to tell the printer to change filament when I was done using it for the day and and pull the filament out of the feed tube.  That way the filament is back on the spool and not under as much stress, but it is a hassle to remember to do that.  Why doesn't the filament break while in use?  Apparently when the printer is in use, the filament isn't in the feed tube long enough for the stress cause it to break before it hits the hot end and is turned into goo.  I've got a new spool of grey, but it's not exactly the same shade of grey.  It's from a different manufacturer - I couldn't find a brand name on the first spool when I ordered more grey filament.

Unfortunately the way I usually discover the filament break is when I get a print failure.  I've found that these failures can cause a couple of things to happen, first it REALLY cooks the plastic in the hot end, and second it can damage the PTFE liner in the hot end.  The first thing isn't really that much of a problem and I can easily fix it.  However, I'm down to my last replacement liner and it'll be a few days before the new replacement liners can get here.

Well... I'm not positive, but I THINK that maybe I just MIGHT have finished reprinting the LAST of the grey parts. (Don't quote me on that!) The plastic pooping robot has put in several all-nighters in the last week. There was enough of a difference in color between the two rolls of grey that I reprinted almost all of the grey parts. There were only 7 parts that didn't get reprinted, this is what got reprinted:
Lower frame bottom cover plate
Lower frame
Slew gear spacer
Slew gear
Slew bearing outer race clamp
Slew bearing inner race clamp
Center upper frame
Center frame upper cover plate

Bogie side plates - need 16, printed 18 JIC
Bogie wheels - need 16, printed 20 JIC
Idler yokes - need 2
Idler rollers - need 2

Engine platform
Cab
Cab door
Cab side wall wire duct
Control panel
Cab roof
Cab roof magnet clips - need 2

That's 58 parts total, it makes a rather respectable pile of parts. The lower frame, the group of bogie wheels, the engine platform, and the cab were all overnight parts. I had to print the cab twice, 6 hours into a 9 hour print I started hearing some rattling coming from the printer. The main organic support for the tops of the window openings had broken loose and was banging around inside the cab.

I'm going to install the heat-set M3 threaded inserts yet tonight, then tomorrow I'll start machining parts. All of the rollers have bits of support material that need to be removed and doing that on the lathe will be the fastest.

I was wrong, I wasn't done with the grey parts.... I forgot about the guide strips.  The guide strips keep the track links from rubbing on the top of the frame, and are finishing printing now.  I've done a test assembly of most of the heart of the beast - that would be the rotating assembly.  That went fairly well, there's only one spot where it's binding, but as I mess with it, that binding is going away.  When I first put it together, it would bind up every revolution, now I can give it a little flip and get a couple of revolutions before it stops. 

There's a fair amount of stuff in that assembly, and the clearance between the slew bearing outer race clamp ring and the upper frame center post is only 0.5mm.  I kept that clearance small to minimize the amount of crap that can get into the slew bearing.  The slew bearing is the only bearing on this beast that isn't either shielded or sealed.

This is the mostly complete rotating assembly. 

It's only mostly complete because I still need to install the connectors on the slip ring wires.  Once those connectors are installed I can tear the rotating assembly back apart, install the slip ring assembly in its' permanent home, and put the rotating assembly back together for what I hope will be the last time.  When I've got it torn apart I'll check to see if I can spot, and eliminate, what was causing the binding.  I suspect that there were a couple of printer boogers on the clamp ring and the center post for the upper frame that I missed when cleaning the parts.

Don

I wound printing the lift parts twice.  August was the last time I used the printer and I forgot that I didn't need to scale the parts before slicing anymore - so all the parts were too big the first time.  After a Homer Simpson moment. I took out the 103% scaling, re-sliced, and reprinted the parts.  I then discovered that I had an interference problem between the inner link and the outer link.  The inner link was hitting the edge of the outer link and not allowing the lift to fold completely shut.  After a minor re-design and re-print for the outer link I have what will eventually be the scissor hoist for the dump bed.  Below is the lift in its' folded configuration.

That's a AAA battery in front for a size reference. 


This is what the lift will look like when opened up.

That's a roll of 1" painter's tape that the lift is propped up against.  If my calculations are correct, this should give me almost 60 degrees of bed tilt.  That's an M4 x 55mm screw coming out of the gearbox, and my measurements show I only need about 12-15mm of travel from the lead-nut.  With the gear reduction I've got, that should mean about 30 seconds to lift or lower the bed.  I've still got to build the lead-nut assembly, but it's just going to be an M4 nut, some steel brake line, and a piece of brass for the pivot.

I just found this thread again ... how is the project going?

Tom