Crazy axles idea design

[gonper]

Originally Posted by Gandalf The White

If my brain is seeing that very cool second chassis right, you would need some very stiff springs in order to keep it from being super floppy. The links sharing the same mounting holes on the chassis means that blue "chassis" can just rotate forward an backward (on an axis similar to the wheels spinning, if driving straight), taking the axle with it. This will make the caster change as the load on the axles change.

I could be wrong, but figured I would let you know.

Yes, you are completely right, it actually concerns me as well. And I am not sure how to solve it, any suggestion will be welcome.
Anyway this V2 design is still on the drawing table so let see what come out finally.

I just ordered today the gears, bearings, hardware staff and a couple of different winding motors, in order to start building and testing.

[Gandalf The White]

I believe the best way to fix it is have the links not share pivots, and I think the shocks need to be mounted to the chassis in front (and behind, on the back) of the upper link mounts. If you want to avoid stupid long shocks, then the bottom mount can be on the link, instead on the top as you had in that model. The non-shared pivots with shocks mounted to the chassis should prevent "active load adjusting castor." The chassis can still be pretty small and simple, but not quite that simple

[gonper]

Good suggestion Gandalf. One way to reduce the forces that go throw the shock absorbers is to make a chassis as you say, but that is what V1 Gosainthan is about, and I want to test a chassis-less one so I changed how the links are mounted so more forces can be derived throw the chassis instead of the shocks absorbers.

Here is a picture of the idea, let me know your thoughts.
The crossed links are on the front but I think they will be better if they are crossed on the rear.

[Gandalf The White]

I think you can make a simpler model of 7 "links", the 4 links and the 3 vertical sections. Then anchor one or both ends on a fixed cylinder, so the end vertical links can rotate around a point. If you have all the joints constrained properly, you should be able to move pieces around and see how the castor will change.

[gonper]

Originally Posted by Gandalf The White

I think you can make a simpler model of 7 "links", the 4 links and the 3 vertical sections. Then anchor one or both ends on a fixed cylinder, so the end vertical links can rotate around a point. If you have all the joints constrained properly, you should be able to move pieces around and see how the castor will change.

The CAD system that I use lets me give full movement to the assembly so it is easy to check how the full design performs.
The front castor angle changes around 2º during full suspension travel
Rear castor changes much more, around 20º but actually I want it to perform like that.

With this design traction twisting forces are transmitted throw the links from axle to axle and to the ground throw the wheels with out much intervention of the shocks. So in other words we are linking the front and rear axle and what happens on one will affect the other:
- If the rear axle has more traction than the front then it will push downwards and a little backwards the front axle.
- If the front axle has more traction then it will push backwards and upwards the rear axle.
I hope it will perform like an automated dig/scrub function, but not fully sure if it will be positive, only testing will tell.

Thank you for remind me that I can use a 3 link instead of a 4 link geometry, I was having an issue of interference of the rear shocks with the links, using only 3 links will avoid that.

[Gandalf The White]

Cool, I wasn't sure if you had made this model with that in mind. I would try and avoid 3 link if possible, but if you can do 4 link in the front that should be pretty good, at least to test IRL travel and clearance.

Side note, you using F360? I have found the collision detection to be a little exaggerated during some complex joints, that clear fine after 3D printing the parts. Don't know how bad the shocks interfere, but figured I would mention it.

[gonper]

Cool, I wasn't sure if you had made this model with that in mind. I would try and avoid 3 link if possible, but if you can do 4 link in the front that should be pretty good, at least to test IRL travel and clearance.

Yep I prefer 4 links but I think it is not going to be posible for the rear axle.
What is IRL?

Side note, you using F360? I have found the collision detection to be a little exaggerated during some complex joints, that clear fine after 3D printing the parts. Don't know how bad the shocks interfere, but figured I would mention it.

No, I use Onshape it is quicker and simpler so more efficient at the end.
The shocks do interfiere on the CAD so will do in real world.

Thank you Gandalf for your tips you are a great help.

[Gandalf The White]

What is IRL?

"in real life"

No, I use Onshape it is quicker and simpler so more efficient at the end.

Ah, very similar to F360 visually.

Thank you Gandalf for your tips you are a great help.

Glad I could help. It's not every day you find someone crazy enough to design a motor-on-wheel crawler from scratch, figured I could add my thoughts!

[gonper]

Well here is a picture of the final version of the V2 Gasherbrum.
With a crossed 3 links at the rear.



Here is a picture of version V1 Gosainthan at full articulation.



Now I am just waiting for all the parts, bits and bobs to arrive...

[Duuuuuuuude]

V2 is going to fold itself up. There is absolutely nothing there to support the "chassis", or to prevent either axle from driving under or over it. You would need an almost rock hard spring to prevent that from happening, in which case an incredible amount of stress would be placed on the axle tubes, upper links, and upper shock mounts.

[gonper]

Originally Posted by Duuuuuuuude

V2 is going to fold itself up. There is absolutely nothing there to support the "chassis", or to prevent either axle from driving under or over it. You would need an almost rock hard spring to prevent that from happening, in which case an incredible amount of stress would be placed on the axle tubes, upper links, and upper shock mounts.

Yes you are right all rock crawlers will tend to fold themselves if there is no shock absorbers and limits or they fail
https://youtu.be/CbmduktO9wg?t=4

And yes in V2 chassis needs higher spring rates I have already calculated it, around 150% more on front axle and 190% more on rear axle if a behavior like V1 version is wanted, I think it may work better with a bit more up/down and side/side flex so provably will install lower spring stiffness that those percentages.
In order to handle stress the rods will be 8mm CF tubes. If not enough I can go to 10mm and aluminium rod ends.

Anyway this is V2 version is just an experiment that may not work at all, So will drive the V1 then.

[Gandalf The White]

Originally Posted by gonper

Now I am just waiting for all the parts, bits and bobs to arrive...

Its been a few weeks now, how goes the battle? Still waiting for parts? Looking forward to a test video, or at least some pics!

[gonper]

Originally Posted by Gandalf The White

Its been a few weeks now, how goes the battle? Still waiting for parts? Looking forward to a test video, or at least some pics!

Yes waiting hand over hand.
I ordered everything a few weeks ago but Chinese new year have delayed the shipments. Just today confirmed the shipment of the last parts ordered so everything is on its way here.

I still have not ordered screws and little hardware staff that I will do locally usually takes 24-48h so no big deal with that.
And have to order tires, as I never have cut and shut tires I am thinking in order this cheap ones or this others so I can learn how to do it with out ruining out expensive ones.
Witch ones of those two you all think may be the best ones to cut and shut for a Super?

The plan is:
- Check sizes of parts when arrival and compare with design, modify design if necessary.
- Print pieces on ABS and PLA and build it up, provably some redesign and reprint may be necessary in this step.
- Test it to the limits to see where it breaks and how to improve it.
- Iterate again aiming final design and finally prints on Nylon and/or PETG.

[Gandalf The White]

Originally Posted by gonper

Yes waiting hand over hand.
I ordered everything a few weeks ago but Chinese new year have delayed the shipments. Just today confirmed the shipment of the last parts ordered so everything is on its way here.

That sucks! This is the reason why I (when possible) pay more for semi-local, unless it's like spares or something.

I have to order tires, as I never have cut and shut tires I am thinking in order this cheap ones or this others so I can learn how to do it with out ruining out expensive ones.
Witch ones of those two you all think may be the best ones to cut and shut for a Super?

I think the second link, for me that has 3 "color" options, the third (tiny pins) or maybe second (medium pins) would be my first try. Nice and cheap, and those tiny pins should be good enough to test the printed parts with. Eventually I think you will want something with more side bite than those buggy tires have, but who knows.

Now, I don't have any experience with larger scale performance tires (I own a Summit ), but my "was a 1:24, now isn't" micro Super loves pin tires. And they were not very hard to make, hardest part was a consistent width. I have heard of using a dremel mounted some distance above the table, but I just went at it with some scissors and they turned out alright.

The plan is:
- Print pieces on ABS and PLA and build it up, provably some redesign and reprint may be necessary in this step.
- Test it to the limits to see where it breaks and how to improve it.
- Iterate again aiming final design and finally prints on Nylon and/or PETG.

Sounds good! I think the gearboxes will suffer from heat, and deform before anything snaps. Well, unless the worm gear just shoves out the end!

Good luck

[Gandalf The White]

Actually, those tires you are looking at might not need to be narrower, just taller. I found that was pretty simple, hardest part was making mine the right diameter to fit some micro rims. And if you are printing rims, that won't be an issue.

[gonper]

That sucks! This is the reason why I (when possible) pay more for semi-local, unless it's like spares or something.

Not easy to find locally the materials I ordered outbound... I am a patient person so no problem for the waiting, gives me time to think

I think the second link, for me that has 3 "color" options, the third (tiny pins) or maybe second (medium pins) would be my first try. Nice and cheap, and those tiny pins should be good enough to test the printed parts with. Eventually I think you will want something with more side bite than those buggy tires have, but who knows.

You just convinced me to go for those tires as the propose is just learning and testing will go for the cheapest ones. Probably medium pins as they always can be cut in parts.

Actually, those tires you are looking at might not need to be narrower, just taller. I found that was pretty simple, hardest part was making mine the right diameter to fit some micro rims. And if you are printing rims, that won't be an issue.

Yes I think as well there is no need to narrower the tires.

Sounds good! I think the gearboxes will suffer from heat, and deform before anything snaps. Well, unless the worm gear just shoves out the end!

Heat could be an issue, will see how we deal with that.
I have not added thrust bearings to the worm but they can be added to the design if need.

[FANATICRC]

Any farther along production...is there a mock up we can see I'd definitely like to see a working prototype it has definitely peaked my interest

[gonper]

Originally Posted by FANATICRC

Any farther along production...is there a mock up we can see I'd definitely like to see a working prototype it has definitely peaked my interest

As comments on previous post I am waiting for materials and parts to arrive.

[gonper]

FINALLY I received enough material to start the construction.
I made a mistake and ordered only 2 motors (one of each kind) and I wanted to order 8 motors will reorder...
Still some parts to be received and ordered but at least I can make some progress with this.
Now I am checking sizes and tolerances on the design with the final components.
I am upgrading the 3D printer so will be able to print the first parts in a few days.

[Gandalf The White]

Can't wait for some build pics!!!