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Okay, i just finished re-creating the Kyosho Ultima ST Type-R EP, so i will continue with Marui Hunter.

Stock style gearbox area re-created:



Enhanced rear lower suspension arms. These arms have several enhancements when comparing these to stock arms:

- The "oillles metal" as referenced in manual" bushings are replaced with 10mm od, 5mm id 4mm width ball-bearings.
- I have doubled the bearings. Now 2 bearings per arm vs 1 bearing in stock arm (the stock design was horrible...).

- I slightly altered the inner area of the arm as a favor for those users who still use the stock Marui universal joint and who has worn the shaft to dead state with the stock "oilles metal bushings". This design difference basically cant be seen from outside. This is only visible if comparing this arm against the stock with laying the parts over each other. This change allows the stock universal joint to be moved outwards from the center of the car by 3mm to bring 3mm of fresh metal surface against the bearing (this mod needs my modded parts to work).

- Edit: Added an option to move the outer bearing (the closest to the wheel) 4mm inner for those users who have ran out their axles with #oillesmetalbearings. The package includes the arms and the shims. If you have fresh axles, you install the shim to the outer bearing hole first, then the bearing. If you have "beaten to crap" axles, you will install the fresh bearing first, then the shimm. After that, you should have "new axles".

- When i was at it, I also designed the arm for multi-purpose use, so who wants it to work like stock arm, when talking about the "hinge pin" area (if you can call it like that) the arm has:


* Stock 7mm plastic hinge pin for those who want stock performance and look.
* Stock 7mm plastic hinge pin with replaceable plastic bushings. Just cut off the whole hinge pin, install the supplied 6,5mm bushing with 20mm length M3 screw to each hinge pin.

* Inside the 7mm hinge pin, there's a 2,5mm hole. This is undersized hole, because a multi-purpose use arm. ->
*For those users who would like to replace the stock hinge pin with 3mm screw + ball bearing or plastic bearing, just cut off the 7mm plastic part of the hinge pin with hobby knife and
screw 3mm x20mm screw, and install 3mm id, 7mm od and 3 or 4mm width ball bearings and 3mm ID 7mm OD and 6mm width plastic shim to body.

* For those users who would like to replace the hinge pin with 3mm shaft, just drill the 2,5mm hole once with 3mm drill bit, after that, push the 20mm (length) titanium or steel shaft
through the hole and secure it with set screw and then install
3mm id, 7mm od and 3 or 4mm width ball bearings and 3mm ID 7mm OD and 6mm width plastic shim to body.

To sum it up, this one arm basically covers up all the possible situations i can think of with Marui Hunter. You only need this one arm set and then you can decide what style you want to go with it.

Pics:





The pics are render pics, they miss the set screw hole, but its in the printed arm.

All the parts are 3D printed from 20% Carbon Fiber/ 80% PETG filament. From my personal experience with this filament and my 3D printed Kyosho Ultima ST Type-R EP, i can safely promise that these parts are tougher than the stock Marui Hunter/Galaxy parts.

Edit:

Here are the final "RC as known as release candidate" arms, these pictures also show the set screw hole:

Heres the Enhanced rear lower control arm printed and installed:





Im not kidding, even with my "beaten to crap" axles = zero play and my worst axle was 4,3mm if i recall correctly (yes, this was a real beater when i was kid), at its worst point (right at the original "oilless metal bearing point"). It actually seems that these will be durable enough with only PETG as a material. These 80:s arms had so much "beef" around them, so these are great when 3D printed. Although, i did add a little of "something" here and there.

Alright, i just checked how easy the OT-28 gears are to get nowadays. It seems that those prices are up and supplies low. I made the decision and bought the whole Kyosho SC/RB6/RT6 gear diff from Japan. I probably wont be using the gear case, i just need that set to model my own diff case and final gear. I thought that its a waste of time to develop another diff for the discontinued OT-28 gears, when there are newer and better alternatives available.

So the diff case will be my own design and uses easy and cheap to get RB/RT/SC diff gears. I think this is the best decision for resurrection project like this.

Dont know if there will be any users for these parts, but i take this as a another learning project. To be honest, i wish i could make even small amount of money with these parts to break even, as these resurrection projects haven´t been cheap.

I already have 10x5x4mm ball bearing converted 3D printed OEM look front wheels for sale,3D printed battery holder and rear wheel inserts are also available but not on ebay.

Chassis starting to take shape:







Any suggestion where to cut it? I mean, whats the preferred point of the rear and front chassis cutout. I cant print this on one piece. I need to design the front/rear attachment points and i need to design them to be invisible, yet strong enough. My own thoughts are at the radio box area, or where the OEM speed controller was attached.

If you double the thickness of the bulkhead between the gearbox and forward chassis part then split at that point , add a few descreet screws and maybe a slot together join ?
How are you going to get round a ton of support in the radio box ?

Thanks for the reply Dadio!

Suggestion noted!

I will probably fiddle around with some chamfer in radio box corners, but its also possible to do some clever bridging there. I need to print few protos to see how it should be handled.

Some small additions to rear suspension arms:

- Added adjustable option to lower suspension arms, to deal with positive camber gain during suspension extension movement (during rebound). There are two set screws per arm to offer adjustability to limit arm movement over the neutral camber point towards the positive camber.
- Added option to use example common ebay quality aluminum balljoints as susp links (arm still works with OEM links). (This mod is visible if you look at the small groove that the suspension link attachment point has, that groove is needed for arm to accept the aluminum ball joint and still keep the OEM compatibility).



I have also added small mods to my rear suspension attachment points.

These are bolt on retrofits/repair pieces to OEM chassis. These are 3D printed from Carbon Fiber/PETG and include two integrated M3 brass inserts and drill template that should ease up drilling the screw holes to OEM chassis. I have done my best to keep the design looking as original as possible, but because the OEM design is so flawed i dont know if i can do any more good if i try to respect the OEM design.

Still W.I.P, but:

Had some time to draw the chassis further, still work in progress though:

That's looking really good , I'd be tempted to do a fast test print of the front end to check the fit with stock parts like you have with the rear , nothing worse than printing the whole thing for 8 hours to find a minor mistake and having to do it again specially if you've put fillets in as its a pain to change them .

Thanks for reply Dadio!

Yea, print test will be definitely needed, i planned to section the suspension mount to smaller sections first, print them and assemble them with original parts and if they are okay, then print the whole front suspension section to check if its okay and then finally adjust the design, so it could be 3D printed with 2 pcs. I will have separate designs for one piece chassis and two piece chassis, for those who have access to bigger printers.

I can definitely feel you with your comment about fillets. They look great, but are pure horror when modifying the part.

Yesterday i printed the rear suspension upper mount repair pieces. Fitment is spot on and they seem to be tough (sorry for a crap looks, i just ripped the supports off with pliers and used fast print settings):







I cant remember how brittle these parts were when i was a kid, but both of these have been broken in the original chassis i have since early 90:s so... I have s strange feeling that even when 3D printed from petg, these should be more durable than the original plastic. And because these can also easily be replaced, these should be great replacements to those few people who would still like to drive their Hunter/Galaxy. You can see the print orientation from the pics. Because the print layers are the weakest point, the orientation is that and its supported by the "hinge screw" and the 2 screws that are bolted through the chassis to the 2 brass inserts that are pressed to the repair piece with heat.

Im also fiddling around with the idea of drop in gearbox replacement, that could fit to the original gearbox slot. I dont know if its possible (yet), but thats one solution for those who would like to keep their original chassis.

Try printing the gears , they may not last as long but are expendable for people who want to run them , looks like your using Fusion 360 and there's a gear making tool ,you select the pitch , lash , tooth number and centre hole diameter and it creates the gear .
When printing use a raft to avoid elephants foot , print slow as well , you may have to scale up or down by 1% to get a good mesh .

Thanks for tips!

I have printed gears from CF/PETG to my Ultima ST GP project. I would love to print them from CF Nylon, but i´ve had so many problems with Nylon printing that i kind of forgot it.

SLS printing service is also a solution, but i will start with FDM and 48DP gears. 48DP is easy to print with 0.4mm nozzle and in my cordless drill test i could print pretty durable gears. I dont know how they work in RC use, but its interesting to test and see!

I use FM Gears plugin in Fusion.

Heres an example pic taken from my ST GP transmission gears and diff i designed and printed from Formfutura CarbonFill Black. I suspect CF/PETG is still too soft for longer use, but this is the starting point of tests. I will need to swap to Nylon eventually.

Starting to look like it:





There are still couple of things in the chassis that need to be addressed, but those are small details.

Parted the front part out from the rest of the chassis just behind the servo posts. First proto now printing.

Everything lines up:





And heres the first proto of the 2 piece chassis:

Joined together with 4 screws under the radio box:



Rear chassis flange with holes that accept brass M3 inserts:



Front chassis:



Only visible underside with those battery tray circular thingys. Not visible when battery is installed. The screws are hidden inside the receiver box, so the only thing thats visible are the two small seams were the zip ties are attached.



This design relies strongly for additional support from the battery plate, so it needs to be printed from CF and i might need to beef it up a little.

This design also gets rid of the printing problem (massive need for supports).

The rear chassis will be printed upside down and the front chassis will be printed "normally".

Edit added 2 horizonal hex screws inside the battery tray for additional support. First full front chassis test print should be ready tomorrow.

As promised, here is a quick shot from partially assembled front chassis:



Test assembly with the parts I had laying around:





Front wheels are my own "OEM-style" design. 3D printed from PETG and modified to accept more common bearing size (4x5x10mm).

The front vertical steering axle will be fabricated from 5mm titanium and front hubs will be re-designed to use 5mm bearings, as the original setup was crappy plastic against plastic design.
The front lower control arm hinge pin screws will also be replaced with 3mm titanium axles.
Rear lower arm plastic hinge pins are replaced with 3mm titanium shafts, that accept ball bearings.
The rear monoshock triangles will have bearings as well.

I still haven't received that Kyosho SC6 gear diff, so I'm now trying to save some time and just do the locked rear axle system to check out the gear lash, so I can print the rear rear chassis. I will try my best to design a 3D printable gear swap that's also compatible with stock chassis, but I can't make any promises. The gears will be 0.8mod all the way, so 0.8mod pinion is also needed. I will use 3x7x3mm ball bearings with idler.