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.

Tuesday, 28 October 2014

Moon Bus part 1

Here is another project that has been commenced, I'm calling it a Moon Bus. Below is the rough design thumbnails. The design started with the tyres, I have had a set of Imex truck pull Clodbuster tyres sitting around for quite a few years, but have never had any rims to fit. The other trick is that these tyres did not come with any foams. One of my random Ebay trawls came up with a really cool set of rims that would be perfect for these tyres and a sci-fi flavoured project...

Moon Bus design thumbnails.

 The rims are an older version of the RC4WD Clod beadlocks which are no longer available. I think you might still get a later revised version with a seperate interchangeable hub. These have a 14mm hex socket and came with some splined 14mm hexes designed to mate with the Tamiya Clod Buster splined axles. They are really beautifully machined and this set does not appear to have been used much, if at all. The front beadlock rings have a number of cosmetic non-functional very short cap screws with 8 functional ones like the back rings. The beadlocks actually completely seal the tyre so they remain effectively pumped up without any foams in place. They have sat around like this for several months now and still have not deflated. They have a massive machined hub which screws in to hide the wheel nut and the rims are really thick and quite heavy.

The two chassis plates I made from 3mm aluminium sheet, drawn up in Delta Cad, printed out, spray glued onto the aluminium and all the inner hole radiuses were drilled out. I then used a scroll saw to cut out all the holes finishing up with hand filing.  The blades for the scroll saw although designed for wood will cut thin aluminium but dont last as long. I went through quite a few. These were made way back in 2002. The shape being inspired by the Tamiya TXT-1 monster truck. I was planning to build a monster truck at the time but it never got very far.

My original CAD drawing from 2002.

The plates have been cut and shunted a bit. Originally the idea for the monster truck was for the battery to sit low down on the extended sides, these have now been chopped and moved to support the upper links. The axles are a set from a Venom Creeper that have a manually switchable diff lock. The transmission is from a Creeper as well. It does not have a slipper clutch which could turn out to be an issue. The lower links are Axial machined high clearance links just because they look cool and I already had a pair which I got to try out on the GrassHopper project for which they didn't turn out to be suitable.
It took a lot of fiddling to sort out the shock placement. They have ended up pretty much in the monster truck vertical position. They have to be able to push up the heavy body without it flopping over to one side that the usual angled crawler shock position encourages. The shocks are a set of Hot Racing oil-less ones that rely on air damping. They look cool but I am not all that convinced of their efficacy.
The Creeper axles have a really annoying angled shock link mount so I had to make up a set of PVC adaptors so the shocks could mount vertically without binding. They are captured by some vinyl fuel tubing bushes which permit flexibility of movement. The first set I made were straight but this meant the shocks were too tall so I made some curved versions. The curved versions restrict the steering throw a bit but as this vehicle has 4 wheel steering it may not turn out to be a problem. As yet I have not tested it. The second hole was added in case there was a need for a sway bar set up.

Discarded straight adaptors.

Revised curved adaptors.

These were extremely fiddly to get right. It would have been sensible to have just used Axial axles except that I like the ability to use a proper unlocked diff given that this is not really a hard core rock crawler.
The other difficulty was getting those beadlocks to mount up. I needed some form of widener to get enough clearance so the rims did not foul the knuckles and the links especially when turned. I ended up getting some Integy 12mm to14mm hex adaptor wideners. They came with two sets of barrel nuts, short and long. The long ones were not long enough. Those beadlocks have about 10mm thick hubs whereas most plastic wheels have only about 3 or 4mm thickness. The project ground to a halt for many months at this point while I contemplated what to do. In the end I made my own barrel nuts from some 6mm bolts. I got some 60mm in length M6 bolts and cut off the thread. The remaining bolt shoulders were drilled out and tapped M4 to fit the axle thread and the beadlocks had to be drilled out slightly to fit the 6mm bolts which are actually only 5.8mm in diameter. I have a set of metric drills that go from 1 to 5.9mm in 0.1mm steps, very useful for tapping and clearance hole sizes.

I think the Integy wideners are too wide, if I could find something that has a much smaller offset and a 14mm hex I would swap them out. It would also reduce the amount of tyre scrub when the steering is turned. In an attempt to shorten the offset as much as possible I used machined down Axial narrow aluminium hexes designed for 1.9 sized wheels.

A start has aslo been made on the body. A wooden frame has been cut and assembled. It comes out at about 1/16th scale. I need to get some suitably scaled driver figures. I think the Bruder toy range of figures may fit the bill.

The body is held on by 4 X M4 cap screws which pass through holes in the chassis and thread into plates screwed to the wooden frame.

One of the servos has a servo reversing lead so the 4 wheel steering works correctly in opposite lock.
I need to make up a battery tray and mount the electronics, then I can test it out...more later.

1 comment:

  1. This is truly great! Just this afternoon, I was at a local hobby shop admiring some great sci-fi plastic model kits + a few nice RC models...and wondering if anyone out there had ever tried to combine the two (i.e. - flying RC saucer, moon rock climber, etc.)....and sure enough, here it is! Great work and keep it up! Thank you for sharing.


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