About this Blog

This is about the combination of two interests, Radio Control vehicles and Science Fiction models. Its also about vehicle design. The models have to satisfy two main precepts.

1. The vehicles have to work, ie be driveable, but not nescessarily win any races or rock crawling competitions.

2. The main thing is that they have to look cool.

Sunday, 22 June 2014

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...

Saturday, 21 June 2014

Tools part 1

I thought I might share some of the tools I use regularly in my model making projects.

Measuring and marking Tools.

I work in metric, specifically in millimetres. I never use centimetres always millimetres. Common materials in Australia are measured in millimetres, even builders use millimetres, a full sheet of plywood is 2400 ( pronounced twenty four hundred) by 1200 ( twelve hundred) millimetres. It makes even more sense for scale models. I generally try to aim for a tolerance of half a millimetre, though anything within an accuracy of 1mm is fine. I encourage anyone who has not done so to move to the metric system, it is so much simpler, there are no fractions to contend with, it is base 10, imperial measurements makes no sense in the 21st century. Australia went metric starting in 1970 and officially completed full metrication in 1988. But why do we still have imperial fasteners in our hardware stores? Because our hardware market is driven from the American market who are strangely still steadfastly clinging to the antiquated imperial system. For a technologically advanced country that strikes me as plain weird. Any way enough of that rant.

Metal rulers are the single most important tool, and they get used for more than just measuring. I have a 600mm (approx 24 inches) , a 300mm (12 inches) and a 150mm (6 inch) metal rule. Sometimes (rarely) I also use a 1000mm rule. Apart from measuring and marking lines, they are used for cutting plastic by running a blade along the edge to score the surface and then snapping the plastic along the score line. More surprisingly they are used for bevelling and scraping plastic. The smaller 150mm rule is most effective for de-burring the edges of plastic sheet or PVC pipe which has been cut.
It can also be used as a scraper to remove seam and mould lines. Generally it is held at an angle and scraped across the edge, removing a thin wisp of plastic. Multiple scrapes can leave a neatly rounded or bevelled edge.

I have a similar range of set squares. These again are used for marking and cutting edges at 90 degrees or perpendicular. You can use a smaller square in conjunction with a longer ruler held firmly against its edge to approximate a larger set square.

I use cheap mechanical pencils with a 0.9 mm graphite. The finer diameters tend to break too easily, where the 0.9mm is thicker, stronger and leaves a strong mark. A fine permanent marker also comes in handy where the plastic may be to shiny to mark with the pencil. A good quality plastic eraser is also useful.

A metal scriber is useful especially when marking out aluminium or brass. A handy tip is to use a permanent ink marker with a broad tip to blacken the metal where you want to scribe it. When you then use the scriber you get a very visible bright mark against the marker black which is many times easier to see than a shiny groove on shiny surface. Once the part is finished the marker ink can easily be removed with iso-propyl alcohol, or methylated spirits. Do not make the mistake ( as I have) of using permanent marker pens on anodised aluminium. The marker dye will migrate into the anodising layer and not come out again. In fact on youtube there are tutorials showing how you can use coloured markers to make coloured anodised parts.

Many of these tools last for a lifetime if kept and used well. The angle protractor and the mid size square I purchased at the very start of my first job as a model maker in 1984, I still use them regularly.

The MITUTOYO vernier calliper was given to me by my first employer as a bonus for good work. I use this almost everyday. It is invaluable for measuring diameters of holes, shafts, drills, fasteners,depth of holes and lengths of small items to an accuracy of 0.1 mm.

There is another very useful tool shown in the pictures above ... the cutting mat. The one shown here was left in a window and exposed to the sun for some time, it warped badly. I tried flattening it with a heat gun and then weighting it but it stubbornly refuses to go back to flat. It is a bit of a nuisance and needs replacing. Get the biggest one you can afford. They don't last forever though and don't leave them in the sun. They can also be used for cutting masking tape into thin strips as the masking tape easily peels off after having been cut.

Cutting, Scribing tools

 The picture above shows my yellow Olfa "snapper" knife. This is the second one I have had over the years. These can be very dangerous if not used with due care. It only takes a brief lapse in concentration, I know from experience, I have a large scar to prove it. Never cut (with any tool) towards any part of your body, always away. If you can't make the cut without risking striking your (or anybody else's) flesh, stop and do the job using another method.

The other yellow handled tool is an Olfa plastics cutter. It is generally used for cutting harder and thicker plastics such as acrylic sheet (perspex). It scribes a v shaped groove in the plastic which can then be snapped when the depth is sufficient. It can also be used to scribe v shaped grooves in the plastic for detail purposes. I have re-ground one of the blades to make a scribing tool that can fit close up to a wall where the original longer blade cannot.

The red handled tool is a razor saw blade which fits in an exacto handle. A razor saw is basically a very thin bladed, fine toothed saw, very useful for cutting up model kits for kit bashing or cutting evergreen pipes. Some people also use them to cut up K&S brass strips and tubes though the teeth tend to get blunt quickly. I personally prefer the Zona saw brand which is much stiffer and less prone to bending, and has a wooden handle. I have recently replaced my Zona saw with three different sizes including a flexible flush cutting version which I have found very handy.  The old zona saws then get moved on to brass cutting duties.

The blue handled device in the centre is a de-burring tool. It has an assortment of blades stored in the hollow handle. It is designed for de-burring metal holes, edges etc but is also very useful for the same task on plastic. It tends to remove more material than using the edge of a metal rule.

A small set of side cutters is good for neatly separating kit parts from their sprues and snipping off lugs, pins and protuberances that are not required.

The tool on the right is the nibbling tool made famous by ILM on many of the Star Wars spaceship models from ep4. The Millennium Falcon in particular is covered in panels that have random rectangular notches cut out of their edges, this is the tool that made those notches. It is designed to cut square holes in thin aluminium panels for electronic hobbyists to fit switches and the like and can generally be found in electronics parts stores. At the bottom you can see a piece of styrene that has had a couple of notches cut out and the bits it removes which could then be used as further detailing although the edges as you can see are a bit furry.

Sanding tools

Some tools you can easily make yourself. Above is a selection of sanding sticks and boards that are simply various bits of wood with wet and dry sandpaper spray glued on. You spray both the surface of the wood and the sheets of sandpaper let it dry a bit and then press the two together so that the sandpaper overlaps the edge of the wooden stick. You the cut around the edge of the sandpaper so that it is flush with the edge of the block. The one on the bottom right is a square stick with the abrasive wrapped over two edges so it can sand a right angle. These blocks are only used for dry sanding, not wet. I only use wet and dry abrasive paper even if I am using it dry. It is usually better quality and doesn't shed the grit like the normal sandpaper, plus you can use it wet if you desire. For plastics, I generally use 80 grit for the course sanding and then 120 grit for finer work, with 180 or 240 if I want it really smooth ( rarely). To really polish plastics shiny smooth you can use 400 up to 1200 grit wet sanded. After that you can use specialist plastic polish or even toothpaste.
Once the sandpaper becomes worn, you peel it off (if you can) and put new stuff on, or just make a new stick or block.
For freehand sanding I tear a sheet into four. One of those quarters gets folded over into three layers which makes a flexible but still stiff pad. With the grit face down you fold one side up and over so that the width is now two thirds and of that two thirds one third is grit face up. Then fold the other side up and over the first side so that only one third of the original width is left, with the newly exposed grit side covering over the first fold. The folds are arranged so that the grit is only ever against the back of the paper, never grit against grit which will ruin the cut of the abrasive quickly. Once one side has dulled you flip it over to use the back. When that side is done you swap the folds to reveal the final third and use that. It can be used this way wet or dry. Plastic responds well to wet sanding as does paint and primer. The wet method results in no dust and keeps the sandpaper from clogging.

Part 2 will look at cutting holes and some power tools.

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.

Battery support platform and mini transmission servo.

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. 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.

Jato steering links for toe in adjustment and locking.

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...