AI Desert Racer RC vehicle part 1

 An AI image popped up in my Pintrest feed that stood out as a possible RC vehicle project.

It already has the stance of a typical 4WD basher style rc vehcle and in particular it brought to mind an HPI Savage due to its high centre of gravity.

The HPI has been around in various guises for decades but I have never had one to hand. I started a search for a suitable chassis to adapt and eventually found a Savage XL big block  roller for a suitable price. It is designed for a nitro engine but I am going to convert it to electric.

A number of parts needed replacesent and as usual the deeper I inspected it the more issues I found and the more parts needed replacement. The gearbox housing had a bearing mount that was trashed so the the whole casing had to be replaced. I ordered a new one to discover it was a Savage Flux electric version and did not fit. then After finding the correct case I discovered the electric conversion assumes you already have the gearbox internals from a two speed gearbox and I had a three speed gearbox. More parts later I finally had a working transmission. I still need to figure out an electric brushed motor mount for it. Still it has been a fun journey figuring out all the Savage variations ocver the years and I hm still way under the cost of a brand new Savage.

Given that the image was AI generated I thought it might be interesting to use AI to generate a 3D model for 3D printing. I used a free Chinese online tool to generate the 3D model. After a few goes I thought it did an OK job of interpreting the 2D image but there were few things I did not like. 

One was a few details that it interpreted strangely, such as the nose which is clearly asymetrical however it decided was symetrical. It also joined the figure in the image to the chassis with a long protuberance. 

There were some details on the image that I did not need like the suspension, wheels and main chassis. The general heavy detail in the 3D model wasn't needed as I would manually add that later from kit parts. 

I chose the highest resolution setting when generating the model so it had a lot of triangles in the mesh.

I started by rough modeling the terrapin tyres and placing them in the correct positions as per the Savage chassis I then scaled and adjusted the proportions of the model to better fir the proportions of the chassis. It ended up being wider than the original and the the rear wheels are placed a bit further back.

The next step was cutting away the bits of ythe bodywork I didn't need. 

In the picture below I have chopped away a lot of unneccessary geometry and deleted half the body as the right side will just be a mirror of this left side

Eventually I decided I would be better off re-topologising the model and simplifying the geometry which was took me several days and a few attempts. The rear wing section has been cut off to be done as a seperate piece along with the nose detail section and the canopy. 

The simplified quad geometry was then smoothed and output qas an .obj file for slicing in Prusa Slicer ready for 3D printing.

It was split into threee parts in Prusa Slicer to fit on my Anycubic Kobra Neo printer.  You can see from the grey and yellow colours I was using up short ends from a few old reels of PLA+ to do this first side which took two days to print one side. 

The same process was followed for the rear left and right wing sections, nose detail and top air scoop sections.

The nose I basically modeled completely from scratch using a re-topologised version as a guide. I simplified some of the detail and generally sharpened it up.

Below is the nose section after modeling in quads and then the smoothed version ready for output.

The next set of pictures show the two halves of the wing being printed. It needed some very tall supports which would come loose after a certain height so I would tape the bases and super glue them to the wing in places to make them rigid again. The last photo you can see where I superglued a couple of wedges of foamed PVC to support the supports.

 After a long period of 24 hours a day printing I finally had all the parts to superglue together and place on the chassis to see how it is coming together.

 The cockpit canopy had some 2mm perspex panels glued in. That was temporarily placed in position on to the rest of the body. All the parts have had an initial wet sanding pass to knock off all the high spots of the layer lines of the FDM 3D printing process.

The next task was to add primer and spot putty for all the deepest divots and layer lines, sanding and then spray putty for all the finer lines. Sanding PLA is a chore, its really terrible to sand. If you go too hard it can start to melt and roll up into thin threads. I find wet sanding prevents this friction heat from building up so I use water and wet and dry sand paper 120 grit at first followed by 180 grit to smooth out the heavy scratching. Once the spray putty is on I dry sand with finer grit.

This is the main reason in an FDM print you dont want to have fine detail as it would just get hit with the sandpaper and ruined.. You want clean surfaces that are easy to get smooth and add the detail on top later if required. Panel lines depending on how wide and deep they are will usually survive intact with the sanding and sparay putty process.

The pictures below show the first layer of spray putty. There will be more primer after this and more spot putty and then another layer of spray putty and primer still to go untill the layer lines are mostly all gone.

The body has ended up fairly heavy ( the printed wall thickness is 2mm with a 10% hexagon infill) and I probably could have shaved off a fair bit of weight but it is a balance between weight and strength for something that could potentially roll over or hit an obstacle at speed. Next time I attempt this method I will try harder to make it lighter.

Thanks for looking.

More soon...