Chassis for excavators

[qwest70]

Hello! Not so long ago, I became interested Lego technic and decided to assemble my own excavator based on 8043. I began to design a chassis on Lego Disigner. And now I present to your attention a new chassis. I made it completely independent on radio control with two M motors that can be changed to L motors, and a two-speed transmission, for better cross-country ability, which is switched manually. The gear ratio is 1 : 1 and 1.5 : 1. The chassis has become 3 cm longer - it is 20 studs and 20 cm, faster and more passable than 8043.
I want to know your opinions, ideas and suggestions for improvement.

https://photos.app.goo.gl/pLWJAhrkLgbQsicx9

https://photos.app.goo.gl/u9BBHzmuTSy9ownA7

https://photos.app.goo.gl/UtGjoYUEW6Aj4gzc6

https://photos.app.goo.gl/pD2fxTxMAZBFhk9b6

https://photos.app.goo.gl/vCrHdsWXX5dWx3pQ8

https://photos.app.goo.gl/xFhtM5JCXkzqVDfw7

https://photos.app.goo.gl/ViqR7qVG8FfWWggM6

https://photos.app.goo.gl/TVUwKgE8TWrpRN2R8

https://photos.app.goo.gl/JFmRJjed1vA3BnP4A

https://photos.app.goo.gl/AXv7u1MQ4RnDmCDV9

https://photos.app.goo.gl/HVCucWCKUY3Gae8U8

Edited August 28, 2019 by qwest70

[1gor]

I would use 5 x 7 frames as much as possible, so I suggest you - try to make another one based on frames but use this as reference 

[Ocelot]

Hi qwest! I've built a few similar things and have the following suggestions:

1. If you want performance, it is better to forget the gearbox and connect the motors directly to the sprocket wheels (maybe with one gear reduction). If you look at the popular MOCs of this type (eg- Sariel's (?) ), you'll notice they almost all do this. It's because any advantage you get from the different gear ratios (high gear, low gear) is usually far outweighed by the extra friction that all the gears introduce.

2. Consider having the sprocket wheels (that drive the treads) be non-structural, so the weight of your MOC is held up by the rollers at the bottom of the treads. This is so that the axles in your drive train are not also supporting the load of your MOC, and will make the inevitable addition of suspension easier later on. Also leading to:

3. Those little rollers don't look like they are interfacing very nicely with the treads. It might be better to have them on either side of the tread, rather than in the middle (there are various solutions to this, some people use pulleys or even wheel hubs without the tire).

4. The small gears, especially the thin beveled ones, are not recommended for high loads. I'd definitely want to replace the those, at least with the wider beveled versions; and maybe instead with 36 -> 20 tooth gears for reduction; again, to avoid using small gears for high torque.

5. When using the 'tank' steering (left and right treads moving at different speeds), there is a a lot of shear force when turning (sideways force the tries to 'pull' your treads away from the chassis), so try to take that into account when designing the connection between treads and chassis. This may not be a problem for you depending on weights/ terrain.

Let me know if there is anything more specific you need, or if the above need clarification.

Edited August 30, 2019 by Ocelot

[suffocation]

Just now, Ocelot said:

[...]1. If you want performance, it is better to forget the gearbox and connect the motors directly to the sprocket wheels (maybe with a small gear reduction). If you look at the popular MOCs of this type (eg- Sariel's), you'll notice they almost all do this. It's because any advantage you get from the different gear ratios (high gear, low gear) is usually far outweighed by the extra friction that all the gears introduce. [...]

This above all else

I tried a similar setup, where the friction was further exacerbated by the subtractor unit and the worm gears. So while in theory there should have been a 3:1 difference between high and low gear, the actual difference was barely noticeable and became non-existent with the added weight of the superstructure.

[doug72]

This is a chassis I built some time ago but is still waiting for top rotating section.

Main drive from XL motor with L motor for steering via subtractor unit.

Uses tan thin bevel gears for final drive but could be changed to stronger double bevel gears or worm gears.

Edited August 28, 2019 by Doug72

[qwest70]

On 8/28/2019 at 5:49 PM, Ocelot said:

Hi qwest! I've built a few similar things and have the following suggestions:

1. If you want performance, it is better to forget the gearbox and connect the motors directly to the sprocket wheels (maybe with one gear reduction). If you look at the popular MOCs of this type (eg- Sariel's), you'll notice they almost all do this. It's because any advantage you get from the different gear ratios (high gear, low gear) is usually far outweighed by the extra friction that all the gears introduce.

2. Consider having the sprocket wheels (that drive the treads) be non-structural, so the weight of your MOC is held up by the rollers at the bottom of the treads. This is so that the axles in your drive train are not also supporting the load of your MOC, and will make the inevitable addition of suspension easier later on. Also leading to:

3. Those little rollers don't look like they are interfacing very nicely with the treads. It might be better to have them on either side of the tread, rather than in the middle (there are various solutions to this, some people use pulleys or even wheel hubs without the tire).

4. The small gears, especially the thin beveled ones, are not recommended for high loads. I'd definitely want to replace the those, at least with the wider beveled versions; and maybe instead with 36 -> 20 tooth gears for reduction; again, to avoid using small gears for high torque.

5. When using the 'tank' steering (left and right treads moving at different speeds), there is a a lot of shear force when turning (sideways force the tries to 'pull' your treads away from the chassis), so try to take that into account when designing the connection between treads and chassis. This may not be a problem for you depending on weights/ terrain.

Let me know if there is anything more specific you need, or if the above need clarification.

Thanks for the valuable advice. I will try to use it in the future. I would also like to see more examples of the implementation of such MOC. At the same Sariel`s MOC`s I could not see his solution without instruction.

[steph77]

hi,

Here is mine, very similar to your first design, not that much technic frame in fact.

and the 'final product'

The important thing to now is that they are bogies at the lower part that guide the tracks. All the weight of your future excavator applies on these small wheels.

Therefore, you have to build a structure specifically strong from the turntable to thes bogies, all the rest could be 'deco'.

Steph.

 

[Ocelot]

@qwest70 No problem, glad to help! Look at the work-in-progress photos on Sariel's site, rather than the videos of finished MOCs; they usually show the insides; for example: Sariel's Tortoise seems similar to what you are doing. Also, this video by Kelkschiz is extremely helpful; it's about suspensions but you can see a few different chassis and wheel designs in there too! There are also plenty of excellent designs by other members of this forum, like this Sherman by Tommy (just as a random example).

Ironically, most of those don't connect the motors directly to the wheels. But I stand by that advice if you want performance!

@Doug72 I've been searching on bricklink for ages now, and I give up: please tell me what that grey curved gear rack (at the top of your MOC) is?

 

 

[suffocation]

4 minutes ago, Ocelot said:

I've been searching on bricklink for ages now, and I give up: please tell me what that grey curved gear rack (at the top of your MOC) is?

I think it's a custom turntable from Shapeways.

Edit: had this in mind: https://www.shapeways.com/product/CBJHXEZWV/turntable-support-13-studs-diameter?optionId=58697999&li=marketplace

Edited August 30, 2019 by suffocation

[doug72]

23 minutes ago, suffocation said:

I think it's a custom turntable from Shapeways.

Edit: had this in mind: https://www.shapeways.com/product/CBJHXEZWV/turntable-support-13-studs-diameter?optionId=58697999&li=marketplace

Correct & it’s very useful, also available at 17L diam.

[Ocelot]

1 minute ago, Doug72 said:

Correct & it’s very useful, also available at 17L diam.

Ah, thank you; I thought it was a new part that I had somehow missed!

[qwest70]

Hello!

Here is my new solution, what are you say?

Edited April 30, 2020 by qwest70

[suffocation]

I think you'd be better off mounting the L motors parallel to the tracks. You'd have one gear mesh less, hence less friction; and you could use the L motors to add structural stiffness to the carrier's critical points.

[Andman]

On 8/28/2019 at 12:49 PM, Ocelot said:

3. Those little rollers don't look like they are interfacing very nicely with the treads. It might be better to have them on either side of the tread, rather than in the middle (there are various solutions to this, some people use pulleys or even wheel hubs without the tire).

I addition to that, take the advice in the quote serious. It will run much smoother. Have a look at 42100, 42069 or especially 42094.

[steph77]

Hello,

I take a closer look at your pictures.

It seems to me you will have an issue with the overal stifness of your chassis.

From my experience, i had difficulties whent 'locking the structure'. I mean, you have longitudinal liftarms and you need to fix them to a perpendicuylar structure that will hold the turntable. In your particular design, this meshing is not still in place and i think you might go with this next.

Keep the work on!

Steph.

 

EDIT: here is another and a bit older example of excavator chassis i built: the main structure is composed with liftarms in longitudinal and transversal orientation locking themselfs

And, as suggested two post up : the Rolling wheels that support the weight of the model can be placed outside the middle of the track like this:

Edited April 30, 2020 by steph77

[qwest70]

The fact is that I want to maintain a visual appearance close to the existing chassis on self-propelled vehicles. And for this, the placement of motors along the chassis spoils the appearance, so for now I'm thinking about options for efficient and easy transmission for transverse placement.

[Jurss]

17 hours ago, qwest70 said:

As far as I know, that greay gear will not mesh with black, those two other gears will skip pretty easy.

[Parazels]

18 hours ago, qwest70 said:

 

18 hours ago, qwest70 said:

Hello!

Here is my new solution, what are you say?

 

 

The connection between the 12 and 20-tooth gears doesn't look reliable enough.

I bet these gears will be chirring under good weight.

Edited April 30, 2020 by Parazels

[agrof]

Beside the above written, the 90° gearing has always has more loss, than 0° or 180°, and needs more proper bracketing. I see here no reason not to eliminate at least one of them. Keep it simple, thus reliable. 

[doug72]

The thin 6L beam is causing a 1/2 L offset in order to give clearence for the 12T double gear gear meaning the 3L connector with centre hole is not fully inserted into the beam at that end.

12 Tan bevel gears are best supported as close to the gear as possible or mounted within a LEGO Black Technic Beam 3 with Axleholes on Ends and Fork (49137 / 87408)

Edited May 2, 2020 by Doug72

[doug72]

It is impossible to mesh a 24T gear at a right angle to a 12T double bevel gear.

Bevel gears cannot mesh with spur gears at right angles - the result will be grinding & tooth damage.

Spur gears with straight teeth are designed to mesh with other similar spur gears.

Bevel gears can mesh with spur gears as long as both axles are parallel.
ie. when you need a 1:2 ratio 

using 24T spur gear and a 12T DBGear

Poor tooth contact and will skip & damage gear teeth.
 

Bevel gears with 90 deg connection.

Stronger tan gear support
.


Edited May 2, 2020 by Doug72

[pleegwat]

There is an exception to that in the old crown gear: A crown gear can mesh with a spur gear at 90°.

https://www.bricklink.com/v2/catalog/catalogitem.page?P=3650b#T=C

[qwest70]

Thank you all for your valuable advices. In fact, there is a hook, but under load, the gears tried to go along the axis and I realized that this was not a classic, and as a result I came to a simpler option.