Make your own foams

I like Imex Jumbo tyres (except for the jumbo Kongs) as they are chunky and nicely proportioned height to width. They are discontinued so are getting pretty impossible to find. In fact wide tyres of any sort seem to have gone out of fashion at the moment, everybody is doing narrow.

I had a pair of the Jumbo Swamp Dawgs but a pair is pretty useless, so I have had a permanent search on ebay for some more. Finally a set of four previously mounted but apparently "unused" turned up and I was the only bidder. With the Aussie dollar being so crap these days and the massively expensive postage costs on top they cost an arm and a leg to get hold of. Eventually they arrived and I was pretty disappointed that they didn't come with any foams. The seller listed them as "ready to mount to the rim of your choice" no mention of a lack of foams. When I queried this he claimed he used to use them for rock crawling without foams ( but hang on aren't these unused). Replacement foams are non-existant and I need them to support the weight of a hefty Sci Fi vehicle so the only option was to make some foams to fit.

 I happened to have a chunk of upholstery foam left over from restoring the seat of a small motorbike many years ago which was exactly the right thickness. I measured up a foam from the new pair I had and made a cardboard template to trace around with a fine point sharpie onto the foam.

The first trick is to cut the hole in the donut shape. To do this you need a drill press and a hole saw with the center drill bit removed from the arbor. The problem is that the hole saw is much shallower than the depth I need to cut so I slowly lower it into the foam, stop the drill press, peel out the foam and then saw a bit more out etc until the full depth is achieved. The hole saw goes through foam very easily and makes a relatively neat cut. The drill has to be removed as it will catch on the foam and spin it out of your hands.

The outside diameter is cut on the bandsaw. Again foam is easily cut on a bandsaw, the denser the foam the better.

When measuring up for the template allow a few millimeters extra on the diameter and a few less on the inside diameter so it grips onto your wheel. As it happens for these 3.2 inch Imex jumbo tyres the hole saw diameter I used for the ID was 86mm or for those still in the living in the dark ages 3 and 3/8 inches.

The other issue with the ebay tyres was the left over chrome plating and super glue still stuck to the rims. I didn't use anything fancy here, no acetone or oven heating, I just used some coarse sandpaper and sanded it off. Worked fine, removed the offending marks of the previous owner easily without any effect to the rubber.

This method can be used to make any sized foams you like and with the right holesaws even dual density foams if you want to get tricky.

Although you cant find the Imex 3.2" rims any more you can still get OFNA monster Pirate rims which fit and are even available in a 17mm hex which is what I will be getting for these tyres for a 6X6 project some time in the future.

More soon...

Giant Tyres and DIY PVC wheels

Readers of this infrequent blog will know I have an obsession with massive RC tyres and recently I acquired 3 pairs of the biggest RC tyres in the known universe, RC4WD's Interco Super Swamper 40 series. These weigh over a kilogram each and are around 250mm tall (10") and 150mm wide (6"). While as of writing this they have stock of the tyres they dont have any of the aluminium rims to go with them and haven't for a long time. Given that the rims are pretty expensive and not available I had to look for an alternative. I tried some Axial Oversized beadlocks. They have a wedge shaped bead receptacle which required that the bead on the tyre be ground to suit. I tried this on one tyre and managed to get the tyre on but the width is way too narrow at 81 mm, the tyre just looked too squashed.
So the only alternative was to see if I could make some rims. I had done an experiment in making rims out of PVC plumbing fittings before. In this case it was to fit some Imex 2.8 tyres. I found it was impossible to locate any 2.8 rims any more as they seem to have completely gone out of fashion. After wandering about the hardware store measuring various parts I found some 75mm storm pipe couplings that fit the inner diameter of the 2.8 tyres. They had a convenient lip in the center of the coupler that I could glue a disc hub to that would be square to the wheel. They were trimmed to the right width from one side to achieve the desired offset, meaning that the disc is offset so the suspension arms will not bind especially when turning the front wheels.

I then needed some rings to glue around the edge for a lip that the tyre seats against. I lucked upon some other fittings that had the right ID that could be cut up to produce the rings.
 

I made the hubs from discs of 6mm grey PVC. These were cut on the drill press using a circle cutting tool. You can see a picture of this in the previous post, tools-part2
I added a bunch of holes and an array of old 1/8th whitworth stainless cap screws I had lying around (as I havn't used imperial fasteners for many many years) for decoration.

 The tricky part was how to add a hex of some sort. In the end it wasn't that hard, though how durable they will be is yet to be discovered. I cut a bunch of smaller discs of the 6mm PVC and drilled a 16mm hole with a speedbit ( also see the previous post for a pic of this) almost the same diameter as across the flat faces of a Traxxas 17mm aluminium hex adaptor. Then I roughly filed out a hexagon shape to slightly less than final size. Using the hex adaptor as a kind of broach it was pressed into the disc of PVC using a vise and some spacers to allow it to be pushed right through the PVC cutting its own profile. The aluminium hex edges are sharp enough and the PVC soft enough to shave off the remaining plastic to leave a tightly fitting hexagonal hole. The whole lot was glued together with PVC pipe cement after having first primed the area to be glued with PVC cement priming fluid ( you can see the pink stain left by the priming fluid) for a good bond.

 Of course the tyres will have to be supeglued in the usual way to stay on. I tried them briefly on a Traxxas E-Revo that I have put Traxxas Slayer suspension arms on and they work fine. I don't know how long they will last if like to beat on your truck and you are pretty dependent on finding PVC fittings that fit the diameter of the tyres you are wanting to house.

After this experiment I wondered if I could get lucky again and find something that would work for the massive RC4WD series 40 tyres. In the pics below you can see them on the left compared with Proline trencher series 40 tyres in the middle and Imex Jumbo Maxx Swamp Dawg tyres on the right, tyres I used to think were huge. In my test of the Axial beadlocks I determined that at least the beadlock rings fit correctly and that as these are available (though discontinued by Axial) I can employ these and try to make a beadlock rim.

A trip back to the hardware store with a vernier caliper to test out any fittings that might do the job. And as it happened I got lucky again and found a fitting that had a built in bead receptacle. Its a 100mm to 90 mm storm pipe reducer. It has an inner lip to seat the 90mm pipe and an outer lip to seat the 100mm pipe that I had to remove with a ball-bearing guided flush edge routing bit mounted in my Makita laminate trimmer (like a small router).

In the photos below you can see the parts that go together to make the rim of one wheel. There is two of the 100/90 reducers, a 90mm coupler, two pieces of 90mm pipe one short and one long and two rings of 90mm pipe split with a small piece removed from the circumference.

 There is also a disc of 6mm PVC and a hex made the same way as before.

The two pieces of PVC pipe are glued into the the reducers and seated against the inner lip. The coupler is then glued over the long pipe that so that it seated against the reducer. The disc is then glued in so that it seats against the long tube. The short tube assembly is then glued so that it seats against the disc. It was pure luck that the couplers were exactly the right length required to space the reducers apart to suit the tyres.

Finally after the glue has dried the inner and outer rim is trimmed to the correct length using a Dremel cutter mounted in the drill press. The outer rim needed to be 2mm shorter than the inner rim to allow for the way the bead on the tyre sits. The depth of the bead receptacle is about 1mm shorter than the depth of the bead so that the tyre bead gets compressed by the beadlock ring as it is tightened down. Finally the rings are glued on the inside of the inner rim to thicken up that area to receive the holes for the M2.5 cap screws I decided to use to secure the beadlock rings. After the rings glue is dry the rims got a final pass with the Dremel cutter.

This process require that the two lengths of 90mm tubing are cut precisely to length and square. Now I used my bandsaw to cut them and although the bandsaw was set up and checked with a set square the cuts still are still not totally accurate. This means that the hubs are slightly out of true and this eventuates in a slight wobble on the axle. Some came out pretty square but a couple were a bit off. With a big lathe you could get these totally on the money ('course with a big lathe you could machine a set of funky beadlocks out of solid), however in my situation, with out a well equipped machine shop it is possible to make something that works and I am not going to be spinning these wheels with a high rpm so I think I will get away with it.

The next task was to redrill the Axial beadlock rings. The pitch circle of my PVC rims is not exactly the same as the Axial ones so I made a jig to drill new 2.5mm holes in the rings. I could only get 3 pairs of the same couloured rings and one pair of those is the skulls design whereas the others are the Tribal design (which I prefer). For the inner rings I used the plain ones from the 3 pairs of Axial beadlocks rims I purchased originally and then managed to fine three pairs of green Holey Roller design rings to replace the ones I hijacked ( for a future project).

 

The jig was a scrap of plywood with a disc of 2mm high impact Styrene (HIPS) cut to the inner diameter of the ring and clamped to the drill table. I drilled a 2mm hole to line up with the original hole in the ring and used a 2mm drill as a locator pin. A new hole was drilled between the existing and on a slightly shorter pitch diameter. then the pin was removed the disc rotated and the pin put back in, thus the old original holes acted as the guide for the new ones. The inner rings were done the same way using another jig with a bigger diameter plastic disc to suit.
A re-drilled ring was then used to drill the 2mm holes in the rims. A split piece of 90mm pipe was used to center the beadlock ring on the hub. The first hole was drilled and a cap screw put in to stop from rotating as the rest of the holes were drilled. I did not tap the holes for the m2.5 thread in the rims, the cap screws can cut their own thread as they are wound in. It makes for a tighter fit and the PVC is flexible enough to cope.

For the 6 wheels I need 144 m2.5 cap screws. I ordered a box of 100 m2.5 X 10 cap screws thinking I only needed 72 of them, I forgot about the inner rings. In case I needed slightly longer screws, I also ordered a box of 100 12mm long cap screws. The box of 100 10mm screws cost me $9.90, the box of 100 12mm screws which I didn't question at the time of ordering arrived with a price of $46.00. When I asked about this they said it was because 12mm is not the common size, huh? I need to get another box of the 10mm screws to complete the task. I can say that after putting three of the tyres on the rims my wrist was sore from all the screwing in and I had a blister on the palm of my hand from pressing on the handle of the allen wrench.

You may notice that the rims are painted yellow. I used a spray can of the typical rust guard epoxy paint. That paint sticks very well to PVC as well as aluminium without flaking off. It needs a day between thin coats, I needed three coats here, so its a slow process. Why yellow? well I stumbled across some concept art, in my searches for futuristic vehicles, that really caught my eye and these tyres will be used for a project that will be very close to the original concept, not a replica but as usual, my take on it.

More soon.

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.

Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7,