Mobile Factory 8X8

In the GrassHopper part 2 post I mentioned another project, well here is the very start of it. I have been mulling over this idea for a couple of years now and slowly drawing thumbnails and collecting parts to try out the concept. Below are some of my design attempt rough concepts over the past 2 years. A recurring theme in the concepts has been the suspension system comprising a sprung arm on which is mounted a pivoting bogie carrying two wheels. There are two of these arms reaching out from the centre of the vehicle on each side. The other design goal is that it should look massive, I mean really really big.

None of these designs has really floated my boat as it were. More recently I have been toying with the idea of something that looks a bit like the NASA crawler but with giant tyres instead of tracks. I thought that perhaps it could be a mobile industrial complex like a land based oil rig or a industrial processing facility.

NASA Crawler.

The suspension design first steps.

Mechanically, the idea is to put a motor in every wheel, which is the most efficient way to build an electric vehicle as there is no shafts or transmission. The largest mining dump trucks (used to be Haulpaks now Komatsu) are built this way with a diesel engine driving a generator to produce the electrical power to drive the electric motors built into the hub of the giant rear wheels.

I was thinking I could use Imex Jumbo Maxx Chevron tyres and Jumbo Maxx wheels, eight in total, all powered. For each wheel there will be a 540 sized motor with a gearbox. Each side of four motors and wheels will be driven by a separate speed controller making this a spin steer vehicle. It means I don't need to build any complicated steering mechanism into the suspension bogies and the vehicle can turn on the spot.
To work out what rpm would be required from the motors I temporarily attached one of these tyres and wheels to my Makita cordless drill and spun it up running along the ground to see how much distance it travelled at whatever speed. The drill has a two speed gearbox. At full depression of the speed control trigger, it reaches 400 rpm on low gear and 1200 rpm on high. It seemed that 400 rpm was about right but perhaps a tad slow at top speed. I wanted a bit in reserve so figured 500 rpm would be about right.

One of the issues preventing the realisation of this project is whether I could get another two pairs of the Imex Jumbo Maxx Chevron tyres. I already had two pairs, which I have had for a good number of years but they seem to not be making them any more so sourcing them is getting increasingly difficult if not impossible. When I scored the pair of Jumbo Maxx Claw Dawgs for the GrassHopper project I also scored a pair of the Chevrons so that made six. Could I ever find the last pair I needed? Having a brain wave recently I contacted the distributor of Imex products in Australia to see if they just happened to have any Jumbo Maxx tyres left and did they have any chevrons in particular? As luck would have it they did have 3 pairs of Jumbo Maxx tyres left, a pair of Claw Dawgs, a pair of Swamp Dawgs and... a pair of Chevrons. I ordered all of them through my local hobby store. I now had the required eight tyres. The four most recent tyres had black foam inners which are made from a nicer more damped and flexible foam than the original tyres which have a white rather stiffer bouncier foam. I will have to make sure to mount one of each on each bogie to even things out.

The next obstacle was to get the eight 540 sized 12 volt 500 rpm geared motors needed which I eventually located and purchased from China on eBay. Once the motors arrived I tested them out to see what sort of amps they pull. The plan was to employ two Traxxas EVX speed controllers (one for each side) so I needed to see if they would cope with driving four motors each instead of the two they usually have to cope with in say an Emaxx or E-Revo. No load they pulled about 2 amps each so about 8 amps all up. Under load they pulled about 4 amps each making a total of around 16 amps which I think easily falls within the design specs of an EVX ESC. Motors geared down like this can really produce quite a lot of torque without stressing too much, after all it is not the sort of thing that will be hammered around a race track at wild speeds. This thing is designed to crawl along and look freakin huge.

I laid out the wheels and started to gather some measurements to begin laying out some CAD for the bogies. I have begun to use Draft Sight which is a free 2D CAD program from the makers of SolidWorks. Its taken me a while to get the hang of it. I used to use DeltaCad which I found was very easy to use and simple to learn. Draft sight is different in many ways but once you get over the first learning difficulties, it becomes simple enough. It works more than adequately for what I need. As I will be cutting everything out by hand ( no CNC or even a milling machine) I do the usual trick of marking the centres of all the radii to be drilled on the CAD drawing. A full size print out of this will be stuck to whatever sheet material I eventually choose and the centre popping, drilling, cutting and filing will follow the printed marks.

I decided to build a mock up of the arm and bogie to check out the function of the suspension before I got too carried away. It was quickly built out of wood to check clearances and position of the  shocks for full travel. I managed to score two full sets of Venom aluminium aftermarket shocks for the HPI Savage at run out prices which I thought might do the job. That means there will be four shocks per arm, sixteen in total. They are mounted on a pivoting bracket at each end which I felt would equalise out the force. To stop the bogies flapping about I have mounted a couple of  Venom Creeper shocks from the bogie to the arm. They have to be mounted half way compressed so that they can both move in and out alternatively as the bogie pivots. They don't really centre the bogie as each shock cancels out the other, but they do dampen the movement. You can see in the picture below a strip of PVC clamped to the arm that the dampers are attached to. I moved this up and down and changed the holes on the damper attachment points until it the range of pivot was satisfactory.

Bogie and damping mock up.

Imex Jumbo Maxx tyres and wheels.

Venom Savage shocks.

Once I was confident the mock up had the range of motion required, I was able to transfer the measurements to a more refined bogie CAD drawing and drawing for the arm commenced.

Bogie CAD Draft Sight

Suspension Arm CAD

  More to follow...

GrassHopper part 2

Its been over a year since my last entry, I admit I am the world's most lousy blogger.

There has, in that time, been some progress on the GrassHopper. It took a year, but after having a permanent search for some Imex Jumbo Maxx Claw Dawgs on eBay I got lucky and a pair turned up which would ship to Australia. I swapped out the chevrons and now the rear tyres match the fronts and I think it looks a lot better. The rear wheels are also Imex Jumbo Maxx Diamonds. They have 14mm hexes and were the white nylon versions. I have dyed them red with red RIT liquid dye which I had purchased in the supermarket some years ago. Now, here in Australia, I can't seem to find it anywhere. The powdered stuff you get in little tins does not work at all well for this application.
I have a large old stainless steel pot full of the diluted dye. Every time I need to dye something I just put it on the stove and bring it to the boil and drop the white nylon parts in. I use a bent piece of wire to lift up the parts every couple of minutes to check the uptake of the colour. When the shade looks good, the parts are removed rinsed and dried. The pot is left to cool, the lid goes on and is returned to  the shed for the next time. I have had this dye liquid sitting in the pot for a couple of years with no apparent ill effects to its efficacy.

Imex Jumbo maxx Claw Dawg Rear Tyres.

 Also visible in the photos is the battery support platform, made from a scrap piece of 3mm aluminium which happened to be the right size, here temporarily supporting a couple of 2s lipos. Under the platform is mounted the transmission 2 speed actuating servo for the summit transmission.

Battery support platform and mini transmission servo.

 

The batteries will be housed inside a mock turbine engine thingy which uses as its base a molded styrene Clinique make up container with a matching lid. The lid will be made detachable to put the batteries in and out. The rear nozzles are from a couple of PVC plumbing pipe couplers. They were glued to a couple of pieces of PVC pipe cut at an angle and in turn glued to the container lid using PVC pipe cement. The container was not long enough to cover the entirety of the batteries so it has been extended with some 2mm styrene sheet and in the picture below some kit part detailing has begun. The batteries slide between two inner walls and push up tightly against a PE foam pad on a lip at the front when the lid is secured and cannot move around. You can also see two pieces of half PVC pipe glued into the end for reinforcement for the lid securing screws to thread into.

Battery compartment made from a Clinique make up container.

Test fitting of the PVC nozzles, the angle looked better than straight.

Battery leads exit fom the front.

Some Revell 1/25 truck engine parts in white, and 1/32 Mirage fighter parts in grey.

I still have to figure out a method for making the battery compartment removable, just in case I ever need to tear down the platform at any time. I have also changed the top links of the rear 4 link suspension. I am now using a couple of Traxxas hollow aluminium steering rods which are a bit longer then the original ones I had in there and they are mounted further inboard on the chassis to compensate. This improved the way the axle rotated on suspension compression. I also added a couple of locking links (steering links from a Jato) to the rear axle to adjust the toe-in angle and to stop any hub movement.

 

 I made a mock air scoop for the engine, out of wood covered in 1mm styrene sheet. The scoop section former was made from a short length of dowel cut in half and each side glued to a central block. A textured piece of evergreen siding was stuck to the front of the scoop, sanded flush and then it was wrapped in the 1mm styrene sheet, glued with super glue and clamped until set.

Not shown in these photos, the rounded corners were then coated with car filler and sanded. Then strips of 1mm styrene were inserted into the front of the air scoop using the lines on the evergreen as a guide to make vents. The scoop was then super glued to the top of the engine/battery compartment.

Nozzles point out and slightly up.

There is more detailing to do on the engine and a great deal of body work to go on the Tamiya fighter buggy body. I have built a mounting system for the body. The front secures to a small body post from a venom creeper which is mounted on a 6mm thick piece of PVC sheet, which is a brace between the two Jato shock towers. I had to make it in two pieces and then join it as it was difficult getting the bends done accurately at each end with the correct length between. The bends were done using  a heat gun, masking of the area not to be heated with some aluminium foil. the end is gripped in a vice up the the bend line, heated until soft and bent using a flat piece of wood trying to be as square as possible and ending at the right angle. This brace will also support the 1/10 Tamiya driver figure I also found on eBay. The rear body mount is a slotted piece of aluminium angle supported on two PVC posts attached to another piece of aluminium angle which is then screwed to two convenient screw receptacles on the body. I used proper plastic screws which I salvaged out of old radios, kitchen appliances and computer printers.
There is a button of turned aluminium on the battery support tray the slot slides under and which retains the body securely (not shown).

Tamiya 1/12 driver figure.

Much work has been done up the front in making steering servo support brackets out of 3mm aluminium and blocks of 10mm PVC. The rear chassis had to be lowered relative to the front modified Jato chassis to allow room for the rear most steering servo. Some 6mm spacers were made up and installed. This actually makes the chassis sit more level so it worked out well. A 3mm PVC plate was also installed to house the EVX speed control and the receiver. the EVX control in the photos was an older one that did not have lipo cutoff so I had added a Novak smart stop. I have since replaced that one with a newer one with built in lipo protection and the other one with the smart stop will go into a different model (more about that soon) where there is plenty of room for all the extra wiring.
 

Rear steering servo is a tight squeeze.

 

 

 

 

Front steering servo is mounted up side down.

Aluminium M3 threaded spacers support the servo plates.

The servos I am using are Turnigy 959's built into a billet aluminium case, purchased from Hobby King. They are not the greatest servos by any means but they are extremely strong and relatively cheap if somewhat jittery. They will more than adequately do the job in this application. One odd problem that surfaced is that the EVX esc would not turn on if the small transmission servo was connected to the receiver, its a a Traxxas servo designed to work with this esc. It would work happily if I turned on the esc and then plugged in the servo. To get round this in testing I added a temporary switch so that I can switch in the servo after switching on the esc. It's possible that I need to add an external BEC. The Turnigy servos pull more amps than the Traxxas steering servos used in the models that sport the EVX so they might be pulling it down enough so it wont switch on. I will have to investigate further. Worst case scenario is I have to make my temp switch permanent and remember the start sequence.

Transmission servo switch.

 

The next task is to extend the body work at the front to cover all the exposed guts. The Tamiya fighter buggy body doesn't have any canopy glass either and I want to add some. I am going to have to make a close fitting inside former to attempt to mould some heated thin acrylic. Its going to be tricky so I'm still thinking about how to tackle that one.

Until next time...