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I thought I already had a thread about this truck, but all I can find is something from back in 2016 when I first put it together, back before the Great Photobucket Treason of 2017 (may broken links rest in digital heaven).  So here we go again, with a fresh thread and potentially only some rough ideas of what we had before.

So - to recap - this started life as a Super Clod Buster delivered from an overseas hobby shop (either Tower or RCMart or something) back in the old days of the late 00s.  I believe around summer 2007.  My intention has been to build a scaler from the body and a stick-chassis crawler from the axles, but life got in the way, I didn't find the courage to paint the body and the comp crawling world moved away from sticks and into something else.  The axles got fitted with 4-link mounts and axle-mounted servos and were used for a time on my TXT-1, before being consigned to a box on the top shelf for many years.

In 2016 I refreshed the axles with new internals, converted from TXT wheels back to the original Super Clod, and built a budget racing clod up around a Reign K2-3S chassis.  The end result was a bit of a pig to drive with 4S and Traxxas 550 motors, and again got consigned to the shelf while I tried to work out what to do with it.

Last year, one of my first projects with my 3D printer was to make up some new servo mounts.  These brace the servo against 3 parts of the axle instead of 2, so the transmission case screws aren't being strained and the servo doesn't flop around.  With some 20Kg servos from Amazon, and some slightly revised geometry, it finally became driveable.  However it was still a bit slow on 3S silvercans and a bit too hard to drive on 4S 550s.  On its last outing it broke an RC4WD rod-end while bouncing over the grassy field at Robin Hood Raceway.  For a while I couldn't work out why it broke, but then I took a look at the chassis and realised the geometry is all wrong for racing.

You see, up until I started watching Trigger Kings videos a couple of months ago, I had no idea what a racing clod should actually look like.  Now that I've been educated, I see I was still building my rigs like comp crawlers.  Steep angle on the bottom link, horizontal top link, high middle for ground clearance and don't worry over much about the steering geometry.

Now I understand a bottom link should be horizontal under static sag.  For the best geometry, the top link should be parallel (when viewed from the side) and describe a marginally shorter arc than the bottom link (to maintain the correct caster angle under compression).  I don't fully understand why the bottom link should be horizontal - maybe this is where the suspension is at its most neutral? - but I also wonder if the loading on the rod-ends is reduced with this geometry.  When hitting a bump with a horizontal bottom link, the axle is free to move up and back.  When hitting a bump with an angled bottom link, the axle must move forwards (towards the bump) as well as up.  If my intuition is correct, this will increase the loading on the links and rod-ends.

As you can tell, I'm kind of running on intuition here...

Anyway - I can hardly make the rig worse than it is.  So, with that in mind, and with my old metal-clad body looking a bit sorry for itself and a completely new JConcepts 1984 F250 body sitting around doing nothing, I figured a rebuild into a classic mid-80s monster truck style is on the cards.

Righto - that is the talking done - now it's pics time!

Here's a side-on view of the chassis as-is.  K2-3S not really designed for Mod Clod builds but it's sturdy and tough.  Geometry is more crawler than racer.  Note tape around bottom links and endbells because of clearance with 550s.

P4190004.jpg

This view shows how much the bottom link wants to come down.  I measured 47mm.  Top links and wheelbase will be adjusted later.

P4190005.jpg

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So, I figured the easiest way to drop the bottom link is to make an extension for the chassis.  I have some 3mm alu sheet which is easy to cut and shape.

Here I traced the bottom part of the K2 chassis onto the sheet

P4190008.jpg

Drew on some dimensions

P4190009.jpg

and duplicated the bottom part

P4190010.jpg

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Two brackets drilled and cut

P4190011.jpg

Filing brackets to shape

P4190012.jpg

and fitted

P4190013.jpg

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Now, there is a problem with this design.  The sharp-eyed among you will notice I haven't yet moved the top links, so the geometry isn't too good.  Ideally the top links should be parallel to the bottom, but the only mounting points would make the top link way too long and detrimentally effect the geometry on compression.  Since I've got an entire Sunday to kill every week and limited supplies coming into the house, it made sense to abandon the work I'd done so far and start again with a nicer drop bracket.

So - here it is:

P4190014.jpg

This time designed in CAD (Fusion 360 sketch to be precise), printed on to A4 and glued onto 1mm plasticard, then drilled through into 3mm alu sheet.  By this time the day was getting long, I was tired, I wanted to get in a quick cycle ride while the air was still warm and had to get showered and dressed ready for the workshop chat, so I opted to annoy my wife by leaving the jigsaw and workmate in place ready to start cutting again when I have some more time.

It has occurred to me that I have the trickiest part of the K2 chassis now in CAD format.  All I really need to add is a selection of shock mount options and cross brace mounts and I've got my own custom chassis.  It would be neat to design it with some nice swooping curves and some relief in the middle and have it made up in carbon fibre.  Well, we'll see how much that costs.

I'll knock up the prototype using my custom bracket and see if the rig handles well.  Then I'll probably have to adjust the wheelbase for the F250 body and come up with a good project name.

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You're getting into ideas that have been forming in my head. I too have been watching the Trigger King videos. But I'm oddly only interested in the retro class. So I've been having the same thoughts on geometry, but applied to ladder bars. 

 

And then I thought of a hybrid chassis. A TVP design, but for ladder bars. They seem to be the lightest and most rugged, so why not try to make them work better? 

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On 4/21/2020 at 11:15 AM, Mad Ax said:

P4190013.jpg

Apologies in advance...in my head this now forever be.. ... the Thongbuster

  • Haha 3

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