Bogger 6x6 part 2

Trawling through my stash for suitable parts I dug out a bulldozer blade from a Bruder toy. I removed the front part of the blade and thought the back part would be good for the rear of the chassis. It needed a  section to be removed from the middle to fit. The two abs halves had all the holes filled with scrap sheet abs and some strips to reinforce the join.

 

 This was superglued to the black foamed PVC chassis . While at the rear end I decided to add some chunky detail to the body.

Two tanks were made from PVC pipe caps with a clear centre box from a broken coffee machine. The teal pipes are from a toy that I discovered on a Jason Jensen Trains sci-fi modeling you tube video. Either side are some reels from an old VHS video tape. There is a further layer of finer detailing to go yet.

Moving round the front I made a couple of transitional boxes from styrene sheet. I also made the base for a communications dish.

Next I thought about an entry door. I have a few round surrounds from battery lights I thought might work as I have used these before. I used an online calculator to print out a template to cut out a fishmouth shape from 1mm styrene sheet to mate with the curve of the hull in the same way as on the Moon Bus project.

After thinking about how much space a sliding door would require I decided to split this housing and widen it into an oval shape. I then drew up a door design in CAD and printed it out fullsize on paper. This was then stuck onto two layers of 2mm styrene stuck together with double sided tape. I could then cut out two doors at once.

Pilot holes were drilled at the radius centres of all the corners and then drilled out to 8mm with a step drill.

Then using a scroll saw all the little segments were cut out. Careful sanding and filing follows to clean up all the edges and then these filigreed panels are stuck to a backing panel of styrene. 

Surround panels were made with some evergreen strips to provide some thickness with the door behind. 

These are then glued into the previously split surrounds with more styrene to fill in the missing parts of the door surround. A sheet of wet and dry sand paper is taped to the hull and a final sanding to match the hull shape is done before super gluing the door assemblies to the hull. Any gaps are dealt with with baking soda and thin super glue.

An exhaust vent has also been added made from an angled hair cutting comb with a styrene duct.

Detailing has also started on the top surface. I found a couple of plastic rulers and glued them on as well as a dome shaped lens cover from a video projector. The grey parts are from a 1/35 scale German railway gun kit.

 I also added a couple of rabbit ear antennas I had made for a previous project but did not end up using. They are on a sprung pivot so they will hopefully bounce back and forward when traveling. The spring system was taken from the switch of rubbish truck toys.

Thanks for looking.

More soon...

 

Bogger 6X6 part 1

 Almost 10 years ago in 2015 I did a post called Giant Tyres and DIY PVC wheels. In that post I showed a method of making some beadlock wheels out of PVC plumbing parts for the super massive Interco Super Swamper 40 series tyres from RC4WD. The tyres are 250mm in diameter (10") and weigh over a kilogram each and I had 3 pairs, planning to make a 6x6.

The tyres in question are on the left with Proline 3.8 trenchers in the middle and Imex Jumbo Maxx (3.2) Swampers on the right.

 Later that year (2015) I did a post about a test rig to see if I could make a motor per wheel set up work using a Traxxas EVX brushed speed control running three motors per side. I found that it did indeed work using cheap 540 geared motors using Imex Jumbo Maxx tyres and Losi ATX tyres with a 500rpm (at no load) gearbox. I determined that due to the increased circumference, 1.4 times greater, the Interco Super Swampers would need gearing down somewhat.

Over the last 9 years I have pulled the tyres and wheels out of their boxes and then  promptly put them back in again. There have been a number of body concepts and chassis suspension ideas all eventually rejected. I had another false start when a purchase of a set of gearmotors turned out to be too weak finally much later I settled on some more 540 brushed motors paired with 160rpm gearboxes that seemed to have the required torque. Last year I made some progress on the chassis of another 6X6, the suspension of which which helped solidify the design for this project. I also had bought a  cheap 3D printer and got used to thinking about making more complex parts for my extremely low budget projects.

In 2024 I finally felt I had the confidence to tackle probably the largest RC scifi vehicle I will ever attempt.

First thing I did was build a prototype suspension arm and figure out the shock position required. I am using Traxxas GT shocks from a Traxxas Summit. These are designed to take the very large leverage of an inboard shock arrangement so are good for a very heavy direct suspension at the expense of considerably reduced suspension travel.

I figured the shock would work at about 30% percent of the distance from the pivot point to the wheel centre. This gave me enough support to hold up what will inevitably be an extremely heavy model, and still have a reasonable amount of suspension travel. Moving the shock further towards the pivot will result in more travel but with less weight capacity and vice versa. Its a bit of a balancing act and I can only judge this by feel rather than by any advanced engineering skills or math.

There is a 10mm flange on both sides of the chassis wall with a 10mm rod holder gripping a short 10mm aluminium shaft. The flanged bearings have grub screws to prevent the suspension arm sliding out. The rod holder is mated to some rectangular 20mm x 40mm aluminium tube via a 3D printed part. All the 3D printed parts were printed in PETG and designed to be an interference fit inside the aluminium tube. They were secured with countersunk bolts and nylock nuts. The  final red parts were printed at home on my cheap Anycubic Kobra Neo whereas the black prototype parts were printed on the Prusa MK4 at work. The Prusa prints are generally much smoother and certainly a lot faster to print but the machines cost considerably more to purchase.

At the other end is another 3D printed motor holder which clamps onto the motor can. These particular motor gearbox combinations came with a mounting plate at the front which is also attached back to the 3D printed motor holder with M5 threaded aluminium spacers. The wheels are mated to slightly modified Traxxas 17mm hubs with a grub screw securely loctited against the flat on the gearbox shaft.

With the suspension sorted out I started on the chassis proper and drew up a side layout in CAD.

Then I needed a cut outline as I was planning to build the chassis out of two layers of 6mm Foamed PVC. Usually I do this by hand as described many times in my projects but in this instance made use of the CNC router I have access to at work. All the mounting holes for the suspension bearing flanges were cut at the same time. It would be nice to have one of these at home but I do not have the space or crucially the cash.

The layers were glued together with super glue after first roughing up the mating areas with coarse sandpaper. The rest of the chassis was built from the same material making a long open box with a 45 degree angle at the front and a 15 degree angle at the rear. 

I needed to finalise a body design. Rummaging through my large object parts stash I found a large acrylic drinks cooler and a purple acrylic bowl. both interesting shapes made from the right sort of plastic and found in charity shops a few years ago. These objects triggered the rough thumbnail design below.

The acrylic drinks holder was designed to hold a pile of ice and keep your drinks cool. It was made with an extremely thick base that needed to be removed. This I did by chain drilling a series of holes and then knocking out the massive lump of plastic. The jagged edge was then sanded out using a drum sander in a drill. You can see one half of the purple plastic bowl in the chassis pictures above.

This was then split in half to become the two sides of a transitional neck section of the body.

I didn't do any cad for the main body structure I just drew up the shapes for cutting out in the Foamed PVC Itself. I decided to make two skinned sides and then join them together with bulkhead frames after the sides were done. The bulkhead frames were made from 6mm foamed PVC.

I started with the side profile frames cut from 3mm foamed PVC. I used material from old signs they were throwing out at work for a good proportion of the construction. This is the reason they have odd graphics on one side. The biggest aggravation from using this sign material was that the printed graphics were covered with a clear protection sticker that I had to laboriously peel off as it prevented the superglue from adhering properly. It was extremely challenging to remove and then it left old sticky gum all over the surface which then was another nightmare to clean off. I used a citrus based gum remover and even that had a hard time getting it off.

The corner radii were drilled out using a 20mm step drill and then the waste material was cut out using an OLFA knife and steel ruler along with a jigsaw.

This side structure was then skinned in 3mm foamed PVC with a few darts (wedge shaped cuts) here and there to make it conform to the compound curved shape. Super glue works extremely well on PVC though I still rough up any glossy mating surfaces.

The two sides were then brought together with more 6mm bulkhead frames. The body sits on two rails of 10mm PVC on the inside of the sides which overlap the chassis by 10mm.

Strips of 3mm foamed PVC were then glued as doublers 3mm below the top edge and the top surface filled in with more 3mm sheet foamed PVC. The front cockpit section was cut into a curved shape. 

After toying with 1/35 scale I decided to scale this model at 1/24 scale which still makes it a behemoth.

At the moment the body measures 1130mm (44") long and 600mm (24") wide. I put some seated 1/24 figures roughly in place for scale.

I wanted to test out the chassis so proceeded to wire up the 6 motors and two ESCs, built a battery section housing the four 2s lipos and installed the receiver.

I 3d printed some grommets to feed the two 14AWG silicon wires through the chassis walls.

The Traxxas EVX ESCs I am using in this model are the older versions without a LIPO cut off feature. To surmount this omission I have added a Novak Lipo cutoff in line with each ESC. Channel two on the receiver drives the left side wheels and channel 3 drives the right side. The right side ESC also provides the BEC to power the receiver. This means the left side Novak Smart Stop has had the red wire carefully removed from the plug so that only the single BEC is sending power to the receiver.

There is still a booster board to be added to power the 12 volt lighting circuit and a pololu switch to remotely switch the eventual lighting on from the transmitter. The booster board takes 7.4 volts from one of the battery's balance plugs and boosts it to 12 volts losing some current in the process but as all the lighting will be LED strips it wont matter a bit.

I also added a pair of strong magnets to both the front and rear of the chassis and to the body as a hold down system. We will see if this is sufficient in due course.

Thanks for looking.

More soon...