Author Topic: Tracked Cat delta skidsteer  (Read 522 times)

Offline ddmckee54

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Tracked Cat delta skidsteer
« on: September 07, 2018, 05:37:50 PM »
I've been converting one of these Bruder Cat delta skidsteer toys to RC for some time now.  It's been on the back burner for a long time because I've been learning how to use the printer, draw in 3D, and upgrading my Chinese clone Prusa I3 into a usable machine that gives me predictable results - not just pretty looking junk.

I'm working on something similar to this:http://www.scale4x4rc.org/forums/showthread.php?t=48900
I'm using a similar gearbox to what SmallHaul used, but I've changed out the motors from 3 volt motors to 6 volt motors.  I had originally planned on a 6 volt ni-cad pack but now I'm wondering if I shouldn't upgrade them to 9 volt motors so that I could run a 2s LiPo battery pack. The drive motors will be controlled by a T-Rex controller and I am planning on printing the drive sprockets.  I've printed a test section of the hex shaped drive shafts coming out of the transmission and that fits just fine.  I've also printed up a 9 tooth drive sprocket for the track belts but I've still got some clearance issues there.  0.2mm is apparently not enough when 3D printing, at least on my machine it's not.  When I've got a usable prototype part I'll take a picture for Show and Tell.

I don't plan on using servos for the bucket lift/lower or the bucket tilt.  Or is that bucket curl?  I don't know - I'm just a lowly EE, you construction types can correct me.  My plan is to use screw drives for these functions with the motors controlled by a T-Rex Jr. controller.

This little project is one of the reasons that I got my 3D printer, to make parts for this.  I spent most of Labor Day weekend drawing this thing in 3D.  So I guess maybe I better get on the stick and get busy making some usable parts.

Don
« Last Edit: September 10, 2018, 02:22:02 PM by ddmckee54 »
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #1 on: September 10, 2018, 02:20:44 PM »
Well I printed out a bunch of junk prototype parts over the weekend, even took some pictures.  Unfortunately I didn't remember to download those pictures from my camera, which is still sitting at home on my desk.

I printed the parts for the track drive sprockets.  They look real pretty and they're even a nice snug fit on the 2.6mm hex drive axles from the Tamiya gear box - unfortunately they don't fit the treads.  The treads are a flexible rubber band with hard plastic tread plates bonded to the inside of the band.  I measured the width of the plate at 6mm, I couldn't get an accurate measurement of the gaps between the plates so I measured the length of 5 plates and spaces by measuring from the leading edge of the 1st plate to the leading of the 6th plate, this measured 50mm.  So I've got a 10mm pitch between the links.  When I wrap the tread around the existing Bruder "drive sprocket" it looks like 9 "links" will fit.

So, 9 links at 10mm per link gives me a circumference of 90mm.  Dividing this value by Pi gave me the outside diameter of the "drive sprocket" with 9 teeth.  I used that value when 3D modeling the sprocket.  But when printed, the first version didn't fit.  I didn't allow enough clearance at the bottom of the pocket for the guide tabs and they bottomed out holding the track plate clear of the side plates of the drive sprocket.  I redesigned the pockets and reprinted the sprocket, it fit the track plate just like it was designed that way.  When I tried wrapping the tread around the sprocket to check the spacing it didn't fit.

WHAT THE F----!!!!  I re-measured everything and came up with just EXACTLY the numbers that I was expecting, so why doesn't this stinkin' thing fit.

Late yesterday I had an AHA moment.  I realized that the 4mm gap between the tread plates was not located where I was originally thinking it should be.  I was thinking that it was on the side of the plate that contacts the drive sprocket, it's not.  The contact point between the tread plate and the drive sprocket is at least 1mm closer, the thickness of the plastic plate, to the sprocket axis.  I modeled it again, this time using the brute force method.  This time the diameter to the contact point was about 28.5mm, as opposed to the 30mm-ish that I was using before. 

This time I may just have a winner, I'm going to reprint this tonight and find out.  I'll take pictures of the before and after versions.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #2 on: September 11, 2018, 10:52:42 AM »
Since nobody believes you if you don't gots pictures, I GOTS PICTURES!

The first attachment shows the 1st, 2nd and 3rd failed attempts at making a usable drive sprocket for the tracks.  The group in the lower left was the 1st attempt.  The "sprocket" was SUPPOSED to fit into a pocket.  My printer doesn't make neat and reliable bridges - yet.  The group in the lower right is the 2nd attempt which eliminated the large pocket.  That part was a success but it didn't fit the tracks properly - not enough clearance at the bottom of the openings for the track plates.  In the 3rd attempt, that blue part on the gearbox axle I went from a 2 piece assembly that would be glued together to a 4 piece assembly that is bolted and glued together - still didn't fit as shown in the 2nd attachment.

The 4th try was the charm, not the 3rd, as shown in the 3rd attachment.  When I wrapped the track around the drive sprocket and it fit just like it was designed for it, I couldn't resist.  I had to put it on the skidsteer and see what it looked like.  I've got some clearance issues, 4th attachment, but that 's just a matter of getting rid of a little plastic.

Next step will be to get rid of those fake rollers on the track frames and make them working.

Don

Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #3 on: September 12, 2018, 02:28:54 PM »
Well I've accounted for the clearance problem between the drive sprocket and the existing skid steer frame.  The clearance problem is STILL there but at least I now know why it's these when the model showed plenty of clearance.

It would seem that some dummy drew the track frames 4mm wider than they actually are.  Discovered that one when I printed the frames for the left track rollers and they didn't fit - not even close.  Since I copied, pasted, and modified the left side parts to get the right side parts I compounded my error.  In my defense most of the original 3D modeling for this was done over the Labor day weekend and there were a couple of LATE night sessions in there - maybe I should have quit and gone to bed a little earlier?

Anyway, I'm in the process of fixing my Boo-Boo's and will soon print test parts for the left side track roller frames.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #4 on: September 13, 2018, 02:17:08 PM »
Forgot to mention, both the track roller frames prints failed about 3/4 of the way thru the prints.  I'm working on the reasons why they failed, but with what I have discovered so far I believe that I can safely assign most of the blame for the failures to myself.

Tried some stuff that didn't work, tried other stuff to fix it and just generally mucked things up.  You know how it goes.

Last night I think I figured out the root cause/s and started fixing the blunder/s.

More to follow,
Don
« Last Edit: September 14, 2018, 12:06:21 PM by ddmckee54 »
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #5 on: September 14, 2018, 12:29:13 PM »
The night of the 12th I also printed half of the left hand side track roller frame.  The extruder gear started "popping" as it was printing.  By this time I was wondering if I was printing too fast, 60mm/sec.; and if I was printing at too low a temperature, 200C.  So as the part was printing I did two things, I slowed down the feed rate and I cranked up the temperature.  By the end of the print I thought I had found the sweet spot for both the temperature, 220C, and the speed, about 50mm/sec.

Last night I made the changes to my Slicer setup and I managed to test them on one of my 20mm test cubes, it printed OK.  When I tried to print the other half of the track roller frame the extruder drive gear started "popping" again.  Apparently the 20mm test cube was not large enough to put enough of a load on the extruder for the problem to show up, so I slowed the feed rate down another 5mm/sec.    It printed the rest of the part without any issues.

They were just the wrong size, working too late at night over the Labor Day weekend strikes again.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #6 on: September 17, 2018, 03:02:20 PM »
I spent the weekend TRYING to print a test part of the motor/transmission mount, I SUCCEEDED in printing a bunch of junk.  No matter what I tried I COULD not get that blue PLA filament to reliably print.  Sunday afternoon I threw in the towel, I changed out the blue PLA with white PLA and 4 hours later I had a transmission/motor mount.  It's not perfect but it IS usable.

Don

Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #7 on: September 20, 2018, 03:58:46 PM »
Maybe the motor mount's not so usable after all.  Last night I started wondering where I was going to put the battery pack and how big was said battery pack going to be?  I might have to lose part of the motor mount to get room for a decent sized battery pack.

I can get a 2S 2400mah hardcase battery pack that will fit in the available volume.  Or I can get a battery pack with upwards of 5000mah that's about 104mm long.  I've got 110mm between the axles but that means I'd have to lose part of the motor mount.

According to Tim Allen more power is ALWAYS better, but I've got no idea how long a 2400mah pack would last in this application.

Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #8 on: September 24, 2018, 05:25:36 PM »
I printed a bunch of junk over the weekend, and a few good parts, but I didn't take any pictures.  I'll take some tonight when I get home.

I switched my slicing software, I went from Slic3r to Simplify 3D, and I like it a LOT!  With Slic3r I always had trouble printing a thin wall, >1.5mm thick, without leaving a gap in the perimeter.  When Slicer couldn't fit all the required perimeters in the wall it would just leave a gap, I eventually just gave up trying to print a solid wall less than 2mm thick.

When Simplify 3D can't fit in all the perimeters it too will leave a gap, but then it will fill that gap in the perimeter with solid infill - no more hollow walls where they are supposed to be solid.

The part that gave me the most trouble was the replacement radiator grill.  On the original Bruder model this is a solid part.  I wanted to open this up and mount a cooling fan under the grill.  Partially just because I could, but also because it seems like I'm trying to fit 10 pounds of parts into a 5 pound sack and some of those parts have a tendency of getting a trifle warm.  Battery packs and drive motors for instance.  A cooling fan won't hurt anything and it just FEELS right.

The first time I printed it the grill ALMOST fit.  The width was a little too tight, so I took off 0.5mm and printed it again.  The curve where the angled grill meets the counterweight was not quite right, but it was acceptable.  However it was TOO long by at least a mm, maybe two.  So I took a mm off the length and printed it again.  IT STILL DIDN'T FIT - too long!  WTF, I cut it off twice and it's still too long?  This started an almost day long adventure into checking/verifying slicer and printer settings and calibration.  The most frustrating part was that everything checked out as being OK.

All right, what is going on here?  This part starts out at a 13.5 angle from the print bed.  I rotate it so that it builds flat and doesn't require support to print.  Is that rotation is causing the issue?  I'm going to take another 2mm out of the length, print it, and fix the fit with a file if I have to.  So I take 2mm out of the length, fix the hole size for the cooling fan mounting bolts and print it - again.  WTF???  It's 4mm too short?  How'd that happen?  I modified the 3D cad file and saved it, check? Check!  I saved the STL file after I modified the 3D file, check?  Ummm... awww-CRAP!!  I wasted most of a day because somebody forgot to save the stinkin' STL file?  It's obviously time to hire some competent help around here.  Crueby gets shop elves that work for cookies, and all I get are stinkin' shop gnomes that sit around claiming they're on their break and threatening to file grievances with the union?  I guess you get what you pay for huh?

Pictures will follow.
Don
Too many irons, not enough fire.

Offline ddmckee54

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Re: Tracked Cat delta skidsteer
« Reply #9 on: September 25, 2018, 01:57:47 PM »
Since "It didn't happen without pictures", I brung pictures.

The first attachment is the radiator grill/cooling fan fiasco.  I don't wanna talk about it.  Let's just say that when I screw up, I don't do it in half measures.

The cooling fan that is mounted to the radiator grill will blow air down over the TREX board, onto the drive motors, across the battery pack and out the opening cut in the floor of the cab.

The second attachment is my "helpful" shop gnome.  "On his break"!  Again!! As usual!!!  I've REALLY got to get that union contract out and read the fine print to find out just how many "breaks" he's allowed, and how often.  I think I'm gettin' Flim-Flammed here.

The third attachment is the transmission mount, transmission/motors, TREX driver board mount, and TREX board in what will be their permanent homes.  With the re-designed transmission mount I've got room to slide in just about any capacity 2S Lipo battery pack that I want to use.

The fourth attachment is my "helpful" shop gnome doing what he considers to be helping.  I guess it really is true, if the only tool you have in your toolbox is a hammer then every problem looks like a nail.

Don
Too many irons, not enough fire.