90 ton 1/14 metal excavator scratch build w/embedded PC
 

I've always wanted to build an excavator, and now the time has come!

The main goal of this project is to build an excavator that can dig normal dirt like you'd find in your own back yard.

Some subgoals:
- Minimize work
- Try to make a simple design (input wanted! :-))
- Minimize cost
- Realistic sound
- Realistic operation (smooth movements, etc)

I'm trying to minimize work and cost by using off-the-shelf standard components like ball bearings and sprockets. I also try to design the parts so that the CNC cuts are simple and quick, and the same thing for the 3D-printed parts. But even so, the project is probably going to turn out to be a massive amount of work anyway.. ;-)

I've selected the CAT 390 as the model for the project, but I'm not trying to make a scale replica. Rather, I just want a functioning machine with a simple design, and that will in many cases not be similar to the original CAT.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0001.jpg

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0002.jpg

The 90 tom CAT is large enough to dig some serious dirt while still at the 1/14 scale that will match my other construction RCs.



For the controls, I want to use an embedded PC for this project too. It gives complete control of the controls, the movements, the sound and also video streaming (for first-person views from the driver's seat). I've made two projects previously with this approach, and I felt it worked our well:
- Bruder MAN truck: http://www.scale4x4rc.org/forums/showthread.php?t=80393
- Bruder CAT delta loader: http://www.rcsparks.com/forum/thread...dded-pc.36063/


Here is the design for the undercarriage:

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0010.jpg


Stein :-)

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The two side rails (is that the right name?) are made of a aluminum + ABS sandwich construction. The outer sides are 3mm 6082 aluminum, which is easy to machine. The ABS in the middle is 3D printed black ABS (Verbatim), printed at 50% infill (very strong).

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0651.jpg

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The motor mount for the drive motor is milled from 6mm 6082 aluminum.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0653.jpg

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The bottom rollers are industrial ball bearings with a U-groove:
- SG20 U Groove 6x24x11mm Sealed Ball Track Guide Bearing

The bolts are standard hex socket cap M6 bolts 40mm long. I'm going to use black bolts when the undercarriage has been painted.

The washers are 1mm thick. I use two in the middle to get the right width.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0656.jpg

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0657.jpg

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Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

looks good

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Off to a great start, this looks like it will be nice , heavy duty. Keeps the pics coming!!

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The main frame is made very strong, as this component is the one that prevents twisting in the undercarriage.

It consists of a roof and a floor in 6mm aluminium and the vertical parts in 12mm aluminum. I've not mounted the floor yet, as I want to have some room to build the swing mechanism.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0675.jpg

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The main frame attaches to the side rails with eight M4 40mm bolts. I'll use black bolts when the undercarriage has been painted.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0681.jpg

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

I was thinking a lot about if a track tensioner is needed. It adds quite a lot to the complexity of the undercarriage, and one of the goals was to keep it simple. But after some testing, I found that I think it's needed. With the large weight and powerful motor, something has to give when for example rocks comes between the drive sprocket and the track, and it keeps the track tensioned so that it doesn't detach so easily.

I ended up with this:

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0685.jpg

In this picture:
- A milled idler mount in 12mm aluminum
- An idler sprocket with a ball bearing, 4SR16 (16teeth, 08B)
- Two springs
- Two very long M6 bolts where I cut off the heads
- 16mm steel tube, 18mm long, inner diameter 12mm
- 12mm steel tube, 18mm long, inner diameter 8mm
- 8mm steel tube, 18mm long, inner diameter 6mm
- M6 40mm bolt
- M6 spacer 4mm long

The track I'm using is an industry standard roller chain, but it doesn't have much room for an idler wheel. That's why I'm using an idler sprocket. It helps to avoid derailing the track. The chain type is British Standard 08B roller chain, similar to the ANSI #40 roller chain (1/2" pitch).

The springs are quite strong to give enough tension to the tracks. Currently they push 15kg - 18kg outwards on each track, depending on their position in the milled slot. This seems to be fine. It can't be to low, as the track would loosen when driving into something.

Ebay links:
- Idler sprocket: http://www.ebay.com/itm/British-Stan...-/191502712638
- Springs: http://www.ebay.com/itm/191650948305
- Steel tubes: http://www.ebay.com/itm/111668876683

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0686.jpg

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Temporarily holding back the tensioner with a strip while securing it with a bolt:

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0723.jpg

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Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

:jaw::jaw::jaw: Very nice Work.

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The drive motor drives the drive sprocket directly. A 12mm steel tube (inner diameter 8mm) matches the inner diameter of the drive sprocket and also extends the gear motor axle somewhat.

http://d1t2tbzmskak12.cloudfront.net...IMAG0730_a.jpg

The gear motor is a very common GW31ZY 12V 14RPM 30Kg/cm. The drive sprocket is an industry standard 08B 16 teeth sprocket. The plastic part is just a part I used for finding the correct distance when drilling the holes. On this drive sprocket it currently serves to hold the pin (a M4 bolt cut to size) in place. On the other sprocket I opted to place the hole inside the sprocket and thus no extra part is needed to keep it in place.

Ebay links for the parts:
- Drive sprocket: http://www.ebay.com/itm/321308379034
- Gearmotor: http://www.ebay.com/itm/291536954105
- Gearmotor alt.: http://www.ebay.com/itm/301680855441


http://d1t2tbzmskak12.cloudfront.net...IMAG0730_b.jpg

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Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Like it. Great Job.

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The top rollers are similar to the bottom rollers, but a bit smaller.
The type is SG15 U Groove 5x17x8mm Sealed Ball Track Guide Bearing.

Ebay link:
- http://www.ebay.com/itm/400561381584

The top rollers use an M5 40mm bolt and two M5 4mm spacers on each side to get the right width and position (I've not received the spacers yet, so I just used some washers in these pictures).

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0741.jpg

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0745.jpg

The mount is a bit different than the original CAT 390 (and most other excavators). Normally, the top rollers are only mounted on the inside. I guess this is to avoid rubble being stuck under the roller as it slides down on the tilted suface of the rail. But for this build, keeping it simple, I've just mounted it on both sides like the bottom rollers.

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The tracks are made of an industry-standard roller chain and track pads. The roller chain I'm using is a British Standard 08B 1/2" pitch chain, similar to the ANSI #40 chain. I'm using this chain as it is one of the more commonly used types, and thus the price is lower. It is a bit too big for this model. The 1/2" pitch means that every track pad is 25.4 mm long, and it should really be something more like 15mm long.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0746.jpg

The "ears" are called attachments and there are various standard types. These ones are name "k1 attachments". There are wider versions that also can be used called "wk1". They have two mounting holes on each side. Search for "roller chain k1 attachments" on google to get more info.
- https://www.google.no/search?q=rolle...=lnms&tbm=isch
- https://www.google.no/search?q=rolle...=lnms&tbm=isch


I originally planned to mill all the track pads in aluminum. But then I though I just make some temporary ones on the 3D printer, and they became very tough, so now I'm thinking that I'll keep the plastic ones until they break (or maybe they won't break). It is also a benefit to be able to drive inside without scratching the floors.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0749.jpg

The pads attach to the chain with two M4 bolts 10mm long. I chose a slotted head, as I think it will be easier to unscrew than philips or hex when the tracks get full of mud. On the other side I use two M4 locking nuts with nyloc locking mechanism.

Ebay links:
- Screw: http://www.ebay.co.uk/itm/261605587451
- Nut: http://www.ebay.com/itm/321386920963


http://d1t2tbzmskak12.cloudfront.net...r/IMAG0751.jpg

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0754.jpg


I also overdid the width on purpose, but now I regret it a bit. I like the wide-tracks look, but I guess this is a bit too much. The real model in scale would be something like 60mm wide tracks. Mine are currently 70mm wide.

http://d1t2tbzmskak12.cloudfront.net...r/IMAG0757.jpg

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Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

The first test drive:

https://www.youtube.com/watch?v=AoB3Eev6npk

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Doing an excellent job, for an excavator I think you will be fine with the track pads you printed. abs is pretty durable stuff and by the sounds of it you probably printed them solid. I think they will hold up for you very well. Keep up the good work, can't wait to see what else you come up with. And it's nice you are sharing where you sourced your parts. Always good to know places to get things. :)

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

A top notch build and an excellent documented progress report - pure eye candy!

As Cooper already said, the links where you got the parts are an added bonus!

Looks like you put in a lot of time to figure it all out. :)

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Outstanding work. Thanks so much for posting the links where you got some of the parts used in this build. It'll surely help us when we want to start our own project.

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Very nice job, great ideas and parts used, the motors seems perfect for this application, strong and fits perfect!

Well done!

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Nice start on this build. It's just my opinion but the problem I see is in the next to last picture. The large gaps between the track pads is why I do not like roller chain but I understand why you went this way. It works perfect and is readily available.

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Yes, I also don't like the large gaps. I think on this model it has mostly got to do with the track pad length being too long (25.4mm VS the 18mm it should have been if it were to scale) caused by me using a 1/2" pitch roller chain. I think with a 3/8" pitch roller chain (and the 7mm overlap of the pads that I already have) it would be almost no gap. But even the original model has some gap, though, visible in the very first picture in this thread.

So maybe I'll change the chain to a 06B (3/8" pitch) or ANSI #35 at some point.

That said, after having fastened 38 x 2 pads with 2 screws each = 152 screws by hand, I don't really miss having more pads per track ;-)


Stein :-)

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

Looks great! Very precise. :cool: Hasn't printing in 3d changed this hobby? Imagine where we'll be in a few more years!
Keep up the good work and keep posting pic's :)

Re: 90 ton 1/14 metal excavator scratch build w/embedded PC
 

On our scale the gap in track pads can't be big enough. If they are very close 1.5mm < they will arch up because of dirt/sand particles getting in between them. Not as bad on a crawler track but a pusher track is worse (dozer)