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Plywood Excavator

This project started when my digger obsessed son said 'Daddy can you make me an Excavator?' So I thought sure how hard can it be....

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This is my very first Hackaday project post so I will be updating it periodically. All the photos and explanations are in the Project Details.

I finished the Excavator back at the beginning of 2017 but have only just got round to publishing it online for the world to see.

Please ask me questions and comment as I'd love to get peoples feed back.

The initial concept involved tracing in CAD a real excavator and have my son sit on top of the counterweight whilst moving the controls mounted where the cab would be. I wanted the excavator to work exactly as a real one would so it needed to have the following:

Working caterpillar tracks with skid steer (forward backwards rotate left and right)
Slew (spin round left and right)
Full control over the boom dipper and bucket

Ive got a lot of experience with CAD and CAM so the natural choice was to design the Excavator in AutoCAD and machine the parts using a cnc router using Mach3 for control.



PLYWOOD EXCAVATOR - THE BUILD...

- - - Massive thanks to Steve Knight the ultimate tinkerer for letting me use his mind and his workshop - - -

I have followed projects showcased here on Hackaday for what now seems like forever.  It never ceases to amaze me the ingenuity of people featured so Its my absolute pleasure to post this project here... Thanks Hackaday!

Not entirely sure where to start so apologies if this project reads badly, just look at the pretty pictures and work out how I did it.  I also really struggled to name all the parts or be consistent with naming of parts.  I was just making it up as I went along!

Scale - At first i needed to find a suitable template to design the excavator shape and get the proportions just right to fit a 5 year old.  After some googlefu I found the image below and set about scaling it to fit and tracing lines over the main elements to get a feel for the basic shape. 

Safety First - obviously a small child and pinching parts is a possible recipe for disaster so I took along time to consider safety.

The most complicated part of the machine is the caterpillar tracks and It took me quite a while to figure out how this was going to work.  I was conscious that a small child's fingers could get stuck in the gears and the track links, however I wanted an authentic caterpillar track look, so compromises had to be made.

Caterpillar Tracks - Initially I wanted to use plywood for everything possible even the chain links for the caterpillar track.  Getting the gearing to mesh with tracks was interesting and I found gear generator program and played around until the correct number or track paddles and links where fully realised.  The images below show this development.

The drive gear and chain above had way to many links to be easily fabricated so I decided to reduce the number.

As can be seen the reduction in track links simplifies the entire design.

I then set about trying to make a very slender chain from plywood links.  The images below show the machining of the links.  I don't have a vacuum bed so each link had to be predrilled then screwed down before machining the profiles.

6mm holes for the pins, 3mm for the screws countersunk naturally!

Final profile cut.

Final links ready to be stuck together. Glued and screwed with stainless screws

Machining out the Track Paddles / Plates? Not sure what they are called?  Answers on a postcard please! 

6mm coach bolts to pivot the links and engage with the drive wheel.  The heads where later cut off and replaced with nylock nuts.

The picture above shows the very first iteration which worked well for a bit but the links were very heavy with the many many screws helping to hold them together.  Also the quality of the ply used was not good.  This resulted in the links breaking under strain.  More on that later...

The picture below is of the drill jig for the chain links to mount the track paddles.  I soon discovered that all the screws where increasing the weight and each Paddle only really needed 2...

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  • 1 × 6mm Ply Sheets Of!
  • 1 × 9mm Ply Sheets Of!
  • 2 × Hazard Warning Lights
  • 1 × Momentary Button
  • 1 × Push to Make Button

View all 19 components

  • Revisions to Future Versions

    Alex Lovegrove02/04/2018 at 23:25 0 comments

    Although i'm extremely pleased with the end result I would definitely change a few things to improve the design and function.

    SAFTEY - No small children were harmed in making or operating the excavator.   

    CATERPILLAR TRACKS - The tracks work very well in a straight line and have a lot of power, however when turning on grass they do struggle.  I would install two drives per track and very slightly curve the idlers to improve turning.  On solid surfaces it works perfectly.

    CONSOLE - I would increase the height of console to improve leg room.

    SLEW - The slew swings side to side and doesn't lock into place so Im looking to devise a mechanism to prevent the swaying.  If anyone has an idea then let me know.

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66666 wrote 4 days ago point

Amazing 

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Jones wrote 4 days ago point

How did you come up with this idea

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mark.reeves.78 wrote 02/08/2018 at 19:14 point

Very cool. I like the use of the gear box. I picked up a 4 wheeler that needed a battery for next to nothing awhile back at a Garage sale. I got it running easy enough. Now I feel inspired to turn it into a digger.  I see your breakdown of parts. Are you able to share where you sourced the actuators. The Hazard lights were a nice touch. I do like how you made it look and operate very much like the real thing. I find myself torn between making things authentic and making things work with what I have lying around.

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Alex Lovegrove wrote 02/09/2018 at 12:13 point

Hi Mark,  actuators were found on eBay.  There are a lot of different types, these ones were the cheapest I could find.  If I had the money and made another one I'd choose much faster actuators.  Robot Shop do some fast ones.

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Clif123 wrote 02/08/2018 at 03:23 point

Greatest dad ever! I wish that I had one of those when I was a kid.

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Rob wrote 02/08/2018 at 03:18 point

Out-friggin-standing!!  You might consider some safety fencing in front of the foot area. A foot slipping off while backing up could be hazardous.

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CWC wrote 02/08/2018 at 00:25 point

Alex. I have seen a lot of plywood mechanisms but your excavator is the most awesome plywood project I've ever seen. It is impossible to say what I like the most, in addition to the plywood mechanism, I love the small details like the master switch and the joysticks.

I hope to see more of your creations and I will vote for your project when HaD runs a Plywood Hacks competition. You are a wizard and a great parent. Congratulations!

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Alex Lovegrove wrote 02/09/2018 at 12:15 point

Thanks Rob,  there are lots of safety concerns.  Your right having the foot rest come round the sides could help prevent foot slippage.  

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Alex Lovegrove wrote 02/09/2018 at 12:16 point

Hi CWC I've got lots of old projects that I need to publish so stay tuned.  Thanks for the support.

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John Fu wrote 02/07/2018 at 20:12 point

Amazing...I love this project!

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Morning.Star wrote 02/06/2018 at 08:41 point

Oh man that IS some quality magic. I wish I was a kid again :-D

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Alex Lovegrove wrote 02/06/2018 at 11:44 point

Thanks Morning Star.

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Morning.Star wrote 02/06/2018 at 12:36 point

You should take over the world with that. Seriously :-)

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Dr. Cockroach wrote 02/05/2018 at 23:59 point

Damn, where was that when I was a child in the 60's :-D  Fantastic :-)

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Mike Szczys wrote 02/05/2018 at 23:56 point

This is jaw-droppingly awesome. You're some kind of dark-mage of plywood construction. The tracks are just spectacular, and the functionality of arm, pivot, and driving is all amazing.

Anyone browsing this project, the demo videos at the bottom of the project log should not be missed! https://hackaday.io/project/35093-plywood-excavator/details

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Jan wrote 02/06/2018 at 11:07 point

THIS needs to be frontpage as soon as possible!

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Alex Lovegrove wrote 02/06/2018 at 11:42 point

Thanks Mike, there is something magical about plywood. Thin slices laminated become versatile, beautiful and strong.  Perhaps Hackaday should run a Plywood Hacks competition?  Nudge nudge wink wink! 

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