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I'm using this on my crawler.
www.ebay.com/it...%3A2334524

This can be cut down to length as they use a D shaped shaft hole that goes all the way to the joint.
These just need normal 5mm shaft in both ends to work.

Regarding the drive joint design, you could use something U shaped and make one end rotate.
Maybe something like C-hub and uprights on both sides and one turned 90 degree for up and down movements, while the other is duing the side to side.
There is loads of aluminium upgrades for that sort of parts when you find a combo that work.

I have seen several builds over the years with this sort of coupler, but most of them was on the scale4x4 forum that is no longer.
Germans is very good at the scale game, so there is a possibility that someone have built something that can give you some ideas.


Found this...
kaidev.net/proj.../BV206.php

Found this little gem which shows what the BV206 can do 

What I'd identified as a "custom nut" in my 1st rejected design earlier (and something I thought I'd probably have to make myself) is correctly called a "barrel nut" & is availalble off the shelf

Still waiting on thhe gearbox replacement bits, but some of the stuff I'd ordered has arrived - I'm not sure I'll need the M8 studding or long nuts, or can make do with the assorted M8 fasteners I've already got, but my current thinking is an almuminium plate (ordered last night) fixed to the tail of the lead chassis, with one of the rosejoints fixed to that. Being fixed, I can make a styrene structure to emulate the look of the 1:1 hydraulic setup.

A second rose joint (with as much of a spacer as I can get away with to maximise the horizontal angle between the two chassis) will be fixed under that, with the tail end linked to the nose of the trailing chassis with thrust washers to permit rotational differences between the two chassis.

All that should be enough to show whether an unpowered link will work, or if I really need to go back to plan B

TBH I was initially thinking M12, M10 seemed like a compromise, with M8 being the lightweight option ... I'm thinking i could/should have gone lighter still

Yep barrel nuts is available in most sizes, down to M2 I think.
There is several designs, from a hollow tube to the cable securing ones.

Myself has used M4 ones on several projects, the ones I have used is intended as wheelnuts when using wide wheelhexes. Mostly in crawler appclications, but can be used on all vehicles with M4 wheelaxle as long as the wheelhex is drilled to 5mm bore for the barrel nut to pass through.

Still waiting on those gearbox/pinion parts... I can't prove the supplier's pants are on fire regarding them having a "secondary warehouse", or that the last two examples of one of the parts weren't allocated to my order rather than, say, sold to someone else by a different compant - but I won't be buying from them again. And probably not any other Kyosho item either, if the parts supply for current models is so weak that they are still the "best" option to get them

I often say I'm a Tamiya fan _in spite_ of Tamiya, not because of them, but I really can't fault their parts backup in comparison

Bits finally arrived, 4 weeks to the day I ordered them. Not bad for "in stock" items

 

In french army, this vehicle is named VHM. High mobility vehicle.  Chasseurs alpins use it.

I finally got around to some temporary wiring to test whether basic tank -type steering works, or whether I’d need to work out a much more complicated push/pull hydraulic/ electromechanical skid steer setup. 

Short answer – as a proof of concept, it works   


The first set of radio gear I tried (a Flysky FS=CT6B combo) didn’t make it easy – after lots of part swappery it just wasn’t working on channel 2 (up down on the right stick) with either ESC or the servo. After I’d opened up the TX to check for anything obvious like the x-axis gimbal missing a wire or not being plugged in, the TX failed to power up at all.

I’d bought the in the middle of March this year, described as “new” (but at a “used” price TBH) from a private seller on eBay. I don’t remember testing it at the time so it’s not something I’m going to pursue – I’d have a pretty low opinion of someone who wanted to return something after 10 weeks

Given that some of it worked, then none, I think there’s a fair chance it was working when sold. I’ve kept the RX (now marked as “suspect”) for future testing, but it’ll go in the spares box for the time being. A “new” radio set (an FS-i6 combo, which is basically the same thing but with a big screen) solved the problem


Right stick up & down (channel 1) controls the left ESC, powering both left side motors – which drive the right hand tracks. Left stick up & down (channel 2) does the opposite. The Right hand pot moves the snow plough blade up & down. Side to side movement in the sticks is a distraction to proper steering (i.e. if it moves, the expectation is that it does something, and increases confusion when it doesn’t) so I will make some “gates” to prevent any sideways movement. 

This only leaves one more channel – due to the potential irritation of the flashing amber beacons, I want to be able to switch those from the TX (the left pot), so I any headlights/tail lights/cabin lights will have to be powered via a simple hard switch.   

Trying to carry the thing about showed it’ll need some sort of stretcher. 

Speed with all 4 motors going flat out is probably more than needed for scale appearance, and TBH anything beyond 60% increases noise disproportionately with not that much increase in actual speed – what it really does it get you into trouble with the steering faster. For that reason I will fiddle with the throttle end points at some point, probably limiting the forward travel to 75% (i.e. 60%, plus a bit of headroom).  

Turns -  preferably already moving forward - are accomplished by either slowing the inside tracks (i.e., slow the right tracks for right turns, or left for left turns) or accelerating the outside tracks (or both at the same time, but I will need to practice that) - just like a conventional tank. However, forwards on one track & reverse on the other in a tank will turn on the spot – but in this setup (or using very much reverse throttle at all) quickly results in a 90-degree jack-knife with one set of tracks trying to climb the other.

 I think the weight imbalance (currently one battery in the front, plus the ECS, lots of wire & the snowplough) is contributing to this – the front section is fractionally slower but has more traction, the rear is faster but less grippy. A better weight balance, plus drastically restricting the reverse throttle end points (I’m thinking 25%) should, if not “fix” it, at least put those shenanigans to within tolerable limits.

Turns – when done at a appropriate speed – are pretty tight, much better than a Lunchbox turning left at full silvercan power. Trying to get it anywhere specific though, that’s going to need more practice. Apparent speed is a bit less than a 380 equipped Grasshopper, but is does have an extra reduction step in the gear train. Possibly more like a Clod with two silvercans in “Economy” mode, or a re-release 3-speed in lowest gear (again with a 540 Silvercan). Similar to the latter two in the “lots of whirring, not much speed” as well.  

That’s quite a lot of text – but it reflects what a big stumbling block this could have been (at least in my mind). Instead of all manner of extra engineering and weight, the rest of this build will “simply” be bodywork & tidier wiring

Rather than photograph my diecast Hagglund & make my own drawings, I found a decent “blueprint” @ drawingdatabase...hagglunds/ & used that as a basis.


There were always going to be some compromises in sizing, each can is going to have to be wider in order to not have a huge amount of track sticking out each side, and shorter to fit with the existing chassis & not mess up the steering geometry. Height will be a compromise between making it not look too squashed at the ends, and not too stubby from the sides. 

Width is around 115% of what it should be, length is 92%, and height 109%, making each box 254mm wide, 324mm long, and 179mm tall (before sticky out bits are added). 

Taking everything (loosely) into account, that means a scale of around 1:9, meaning it’ll be roomier than the real thing for Wild Willy drivers/figures, but not so much that I need to be looking for 1:8 figures instead  

The blueprint had no views of the right sides, rear view of cab one, or front view of cab two so I have made some very basic modifications to copies of the existing views, using the diecast version as reference.

These are all a first approximation – already I can see that I’m going to need to narrow the rearmost door considerably, and change the front cab doors to make them look wider, probably sacrificing some of the “B” pillar area & narrowing the “frame” portions around the windows.


Next step is to print all the bits on A4, assemble into something looking like the two cabins & see how it looks 😊

Made the changes to the drawings, printed them out on light card & built them, with cereal packet card tops. I did the rear cab first, and have already made my mind up about a few things – the main parts of each side “should” be slightly curved … I’m not going to do that. It “should” also be a 13-sided open box … I’m not going to do that either, it’ll be a 5 sided open box with rounded edges. The Front cab isn’t going to have the “correct” 15 sides either- just 7. The front of the front cab also needs a lot of height correction due to parallax errors for the 3 planes - 107% on the windscreen, 317% on the engine cover top, and 96% on the front most panel. The front also needs some rework around the edges of the windscreen to account for having straight sides.

I’m going to keep the width & overall height the same, but the sides can be the “correct” length from the drawings – 362mm for the front and 351mm on the rear cab (rather than 324 for both). The front cab can be recessed at the back end to account for the linkage base on the chassis.

I have corrected the drawings, but don’t plan to make another card version. The V2 plans will get printed out on label paper & stuck on to styrene – again I’ll probably start with the rear cab