As mentioned earlier and before I have a Wheely King rc toy. Me being me, that WK is nowhere near stock and I often delight in tinkering with it to make it work better or more fun or whatever.

The thing has run quite well after the last big set of changes (chassis work, lengthening the wheelbase, servo mount on the axle). However since Conny arrived we've had some more...stress testing and some setup ideas turned out to be insufficiently robust in the long run.

The original-original upper link was a cheap and wobbly plastic V-shape and the last owner had sprung for Integy alloy wishbones - which of course were too short for my +11cm stretch. Earlier on I had fixed that by making an extension from a bit of carbon arrow shaft and some glued-in 3mm threaded studs. This worked fine on the bench but over time proved to be insufficient: the threaded bits bent at the contact point with the alloy wishbone, the carbon shaft end splintered and the plastic counterpiece was carved out by the carbon. (Miraculously, everything else failed before the superglue holding in the threaded rods...)

Over time I rebuilt that upper link setup twice, the second time with a one-piece rod: I had some unthreaded silver steel bits of suitable diameter around, but that's way too hard to cut threads in it with my thread die set. So I dug up the gas torch, quickly heat-annealed the rod ends and then threading was no problem. This side held fine, but two weekends ago the other side with the older glue-in setup went pear-shaped: we were with friends with kids, and Conny and Jasper gave the WK a proper stress test, banging into all kinds of things with little subtlety. Also in an obstacle course game with Conny the WK proved to be too unmanoeverable, good for fastish runs but with too large a steering circle. And then I broke one rear shocky shaft; the upper mounting screw had come loose, the shock turned and caught on something on the ground and the shaft went snap! inside the rod end. Great.

So after getting fed up with the upper link non-solution and having to change shocks anyway I decided to mod things further: 4WS, here we come!

This guy has made nice templates for mounting the servo asymmetrically low on the axle, and I used that to fabricate two mounting brackets (my earlier front servo mount had the stervo stick out too far for my tastes). I made them from the 0.85mm steel panels of an old pc case (that's what I had around), which my tinsnips cut without major trouble. The holes and tight spots I did with the dremel-clone and a bit of sawing and sanding.

 wk new servo brackets wk new servo brackets

A carbon arrow shaft was again used to make the steering rods. With one left and one right bracket, the servo directions are the same so no reverser was needed (I use the stock 2-channel receiver). I quickly bolted on a spare servo and some botched up horns and here's the result. Nice.

 wk new servo brackets wk new servo brackets wk new servo brackets wk 4ws

However, testing in the wild on the weekend showed that servo savers are mandatory: the cheap servo in front jumped some teeth on every heavy bump. So servo savers I bought and installed - the local hobby shop had only yellow ones, so now we have yellow-black danger stripes :-). In the meantime I also ordered a pair of cheap metal-geared hi-torque servos (ebay $22 with postage for two).

Then I mounted the (shortish) replacement shocks in the rear and decided to change the suspension somewhat: the lower links moved inboard (as I learned that chassis-inboard-to-wheels-outboard creates least binding), and the front shock mounts moved back a lot, improving articulation quite a lot. Here's how much:

 wk after shock reloc wk after shock reloc wk after shock reloc

With the harder, shorter shocks in the rear there is not much body lean or torque steer, but I still had to trim the lexan body quite some for the wheels to stay clear. Note the pics still show the old upper link extension.

Another weekend with kids having fun went by, and by now the rear upper link extension was totally stuffed. So I decided to build something closer towards perfection: I fabricated carbon* wishbones! (okok, carbon shafts but plastic ends)

The old plastic upper links were sacrificed to reclaim the ends, I cut up a 12mm dia carbon arrow for the shafts and superglued everything together - in stages, trueing the wishbone against one of the extended alloy links mocked up in the old plastic chassis. This worked like a treat, the new upper links are strong and lightweight and I could use the original upper link mounts on the axles.

 building wishbones building wishbones wk old and new wishbones new wishbones in

But I wasn't finished yet: a night-time run in the backyard showed that we could use more light in front and some in the back, too. So I made metal reflectors for the front leds. Then I added red tail lights, and because the motor got very hot on the weekend, a 40mm 12V fan in a custom metal mount. The fan is run off the 6-7.2V battery eliminator circuit that the dinky speed controller provides, which makes it spin less than full blast but it seems sufficient.

Unfortunately, the combined load of the leds and the fan proved too much for the ESC; lights and fan together ran erratically. To fix this I recycled some oldish laptop Li-Ions yesterday evening: the light circuit is now run by its own, separate 1500mAh 7.4V battery pack which, due to the magics of Lithium-Ion batteries, weighs only 86g and measures 50 x 86 x 10mm. That extra pack is velcroed in under the rear lexan body only when needed.

This is how the WK looks now:

 with fan full lights and 4ws full lights and 4ws full lights and 4ws
[ published on Wed 23.04.2008 14:11 | filed in interests/tinkering | ]
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© Alexander Zangerl