[MOC] Wheeled excavator simplified chassis and arm operation mechanism

[SaperPL]

This is something I came up with after starting a build of wheeled excavator from scratch. My previous model had overcomplicated design of the chassis and used small linear actuators for arm movement which was pretty bad for a manual model due to the amount of cranking required. I also got rid of steering elements I often used in my previous builds as they are not that common anymore.

The one of the arm controls use single lever for two arm movements - bucket movement and arm movement - this is made possible by differentiating the torque required for string pull with a wheel.

 

The video shows building of the chassis and operation of this excavator arm prototype

I'm planning to build a full excavator model on this, hopefully with full fledged instructions, but it'll take some time, so stay tuned if you like it.

[vascolp]

Wow, this is very cool!

Small, and with an unusual playability! 

[Oliver 79]

That's incredibly clever. Looking forward to seeing more progress 

[1gor]

Very clever solution 

[The Shuttlefan]

That arm mechanism is brilliant - it's like a modern interpretation of the old flex cables. I'd love to see something like it in an official set. What string does it use?

[SaperPL]

10 minutes ago, The Shuttlefan said:

That arm mechanism is brilliant - it's like a modern interpretation of the old flex cables. I'd love to see something like it in an official set. What string does it use?

Thanks!

I think it's this one: https://brickset.com/parts/6096956/string-30m-w-2-knobs

I got those from Heavy Duty Forklift set.

[m00se]

I think you won the price for "most complex functionality per number of bricks". Really clever.

[iLego]

Just saw the video. This is so cool !!

Wholeheartedly agree with @m00se and others, this is amazing functionality !! Though I have to admit, I don't fully understand it yet 

[Jurss]

Everything is awesome.

Maybe it just misses these tires paired, in pace of those street tires

https://rebrickable.com/parts/56898/tyre-432-x-14-offset-tread/

[SaperPL]

3 hours ago, iLego said:

Though I have to admit, I don't fully understand it yet 

This is pretty simple though - the string pulls by two pivots at the same time, but the bucket moves first because it's move is made to require less torque but longer string pull with this 4185 wheel which acts as a lever. This is similar to putting together big gear and a small gear where you turn big wheel with a small one - your input torque required when moving the smaller gear is smaller and you get higher output torque on the big gear you're moving as this combination works as a lever, but you have to turn the small gear more - the same principle is applied here with this 4185 wheel piece. Then after you reach the limit on the bucket move, there's the arm move which requires more torque but less distance of the string to pull.

38 minutes ago, Jurss said:

Everything is awesome.

Maybe it just misses these tires paired, in pace of those street tires

https://rebrickable.com/parts/56898/tyre-432-x-14-offset-tread/

I've got the 43.2x14 wheels, but it doesn't feel right when put on the front, steered axle. I don't have a good pivot point for it. And when I would put the 43.2x22 at the front and two pairs of 43.2x14 at the back, it looks weird.

[SaperPL]

Update on the project:

 

[BusterHaus]

The lever/arm mechanism is so satisfying to watch. Great work, very reminiscent of the studded Technic sets where functions were a priority over looks. 

[SaperPL]

Thanks!

I've actually tinkered with the arm operation today to reverse the order in which bucket and the forearm? moved and it works, but it got really weak by hanging on single thin liftarm.

[McMarky]

Really great idea and implementation! Congrats!

The only one thing I can complain (but I don't) is that the excavator discharges the load under itself.

To solve this problem I came with an idea that there could be a mechanism that would reverse working sequence of a bucket and a forearm in extremum points. I understand that in this scale it's difficult to implement it.

I mean something like this in the single cable clamshell in this movie:

BTW, I tried to recreate it of LEGO but it was too difficult in usable scale.

 

[SaperPL]

32 minutes ago, McMarky said:

The only one thing I can complain (but I don't) is that the excavator discharges the load under itself.

That's exactly what I'm working on right now by changing the priority between the functions:

The issue is that the return isn't perfectly controllable, it all comes back together, not as I wanted the bucket to fold first and then the arm.

Edited July 5, 2021 by SaperPL

[McMarky]

12 hours ago, SaperPL said:

The issue is that the return isn't perfectly controllable, it all comes back together, not as I wanted the bucket to fold first and then the arm.

Have you tried it under load? Maybe some pins or even dry sand. If it digs something it couldn't be better.

[SaperPL]

On 7/6/2021 at 12:33 PM, McMarky said:

Have you tried it under load? Maybe some pins or even dry sand. If it digs something it couldn't be better.

Just tested it with dry sand. The rubber bands are not strong enough to dig into the sand. Seems like I'll have to rethink the whole mechanism to be made with rigid levers. Thanks for noting this.