Marui Big Bear tires - let's CAD :)

[silvertriple]

Yesterday morning, a friend told me he was said some people would love to see Big Bear tires on Thingiverse... Among my contacts, I have 2 friends wih Big Bear I can chat with when this was landing in my chat, and I contacted them...

First one was not having the tires, as his Big Bear runs on Lunchbox tires... Second one, in Norway has the Big Bear, and the original tires which are mounted on it... I asked him if he can draw the wheels and tires profiles and provide measurements, and explained what I had in mind. He told me he would do that in the afternoon, and later on I received pics (quite a good number, of all faces and profiles, plus drawings and measurements)...

I drawed a profile, made a revolve and started to decipher how I could do the chevrons.... Made multiple tries, not yet happy, as it still require work... But it starts to look alike...






Still some work, to get something closer, but the genral idea is there...

[GoMachV]

Wow! Yes big bear tires are hard to find and I have four flat and rotted ones on my truck so this is of interest to me!

[silvertriple]

Wow! Yes big bear tires are hard to find and I have four flat and rotted ones on my truck so this is of interest to me!

I can already tell you this is not easy... I need to find a way to reproduce the waves on the side... I've not come to agreement with myself on the way to proceed yet

[silvertriple]

The chevrons made turns in my mind during last night. This morning I woke up with few ideas I had to explore. I went to the office, and during my day of work a few other ideas poped up.

I got back to RC stuff around 23:20, it's about midnight, and I may have a good idea on how to proceed with my tries of tonight...


I just have to refine the wave and some bits, and obviously add the other side, but I think I got the way to proceed now... Will refine this tomorrow

@GoMachV I don't have a Big Bear at my end. Would you have some TPU filament and would you like to try a print?

[GoMachV]

I have tpu and plenty of printers but very little experience printing tpu id sure give it a try!

The tpu I have is blue and purple. I was thinking about trying tpe next

[silvertriple]

Wanted to be sure I can derive the other side from the first one, and it works.


Now the next step is really to focus on the way to get the right profile. And eventually to get the BIG BEAR markings on the side

[Dadio]

@GoMachV TPE is more rubber like and better for tires .
For anybody not familiar with CAD thinking what silvertripple is doing looks simple enough ......IT's Really Not Simple , very clever indeed .

[silvertriple]

Tried another way, not happy yet...


Some of my attempts are crashing (con)Fusion360 with a probability of 100% currently
That's not as easy as I envisioned. Will try another way...

[silvertriple]

Multiple tries and (con)fusion360 crashes later



The chevron is slightly too thick at the center, but I did not succeed to get something better yet, as all the attempts to get something better succeed to crash the software... I've send crash reports, maybe that thing will evolve in the futur . In the meantime I have what is considered a release candidate

@GoMachV, i'm going to PM you

[Dadio]

Try exporting as a step file then uploading it back to Fusion , it gets rid of the timeline and just works with what is not what was , really works when Fusion goes black every time you do anything .

[silvertriple]

Try exporting as a step file then uploading it back to Fusion , it gets rid of the timeline and just works with what is not what was , really works when Fusion goes black every time you do anything .

Rethought about it... I'm still unhappy, but I believe I need to do some surface modeling anyway to get the chevron right (which was what I was trying to avoid). Need to do other attempts...

[Frankentruck]

Consider the design capability that was available when these tires were made. Don't overthink it.

[Dadio]

I very much doubt that CAD was used , probably a drawn design given to the machinist , you have to remember that CNC milling was also pretty rudimentary at the time .

[silvertriple]

Consider the design capability that was available when these tires were made. Don't overthink it.

I know that many people would be happy with it the way it is... But still trying to do better.

[silvertriple]

After some feedbacks and further checks on the pictures, I decided to review the model slightly to make the chevron profiles different...

I also included some lettering (a plan under the surface, a text, an extrusion, shaved with a revolve at an offset of .5mm of the surface of the tire).


I added colours in order to make it more realistic


When discussing yesterday with @GoMachV, he reminded me about the support issues I had the only time I tested flexible filament on my own printer: they are a mess to remove, which means it is definitely not going to be easy to print in flexible material using FDM. This turned in my mind the whole night. This morning decided to have a look at few options.

First, I went to I.materialise.com to price the STL in MJF rubber like. Very simple : definitely too much. That won't work.
Then I had a check to see if there was other providers doing similar Rubber like printing online, and it seems that only few printers actually print flexible material.

Ultimately, this tire maybe printable with dual head printer and soluble support materials... Not the usual printer most of the people do.
Maybe printing two halves, integrating the sleeves to act as support could work. I may have to create STL for this...

Next element I thought about is a mould. I decided to do an attempt to create stls for a mould. Printing moulds should not be an issue, and won't require any supports in the important side. Which also means proper finish...
I used the tire model as cut in a mould, and made few parts for this.

The mould would be composed of two parts for each halves.
An external side, with the chevron, and the lettering and the tire side


An internal side


Each halves would be moulded separately, and the center part would be removed before assembly of the two halves.


I believe the external mould would help into this assembly, and I created some elements to make sure the two halves would be oriented properly (one of fixations attachement is bigger to make sure it is proper).


Printing those parts should be easy. a release agent would likely allow for multiple tires from the same mould parts...

I received some feedbacks from a friend with moulding experience and I'll review the moulds slightly, but the general idea is there....

(and while I may not try to print Big Bear myself as I have none, I may want to try to print or mould some buggy tires, and I may try that on some of the other tires I modeled recently)...