Ultima RT5 modernized custom 3D printed chassis.

[HiTec]

No problem! Some people are pretty harsh to judge 3D printing as a manufacturing tech for RC cars. And for a good reason. But as i see it, yes, there are limitations (like every other technique), but the can be dealt with, if the limitations are carefully thought out in the design stage.

Heres something special i thought to add to battery brace (this is just a proto of the brace to check some dimensions).

Sliced in PrusaSlicer so the lower areas are printed with black PETG, then there is 1mm of Glow in the dark filament and finally black PETG again. Looks nice in my opinion even though i didnt took the picture in complete darkness. The rear flap of the brace is chamfered, because i wanted to test how the glow in the dark effect gradually brightens when the layers are added (this is the first time i try that filament).



And heres how it look like when "its not loaded":



Edit: Just finished the rear motor configurations parts. Or well, actually im still missing a rear bumper, but thats not a big deal right now:

[HiTec]

Just finished printing the rear motor support parts

Rear motor installation:

Starting point:



Then goes the 2mm shim plate:



Then the craddle (not bolted on, just took a quick picture):



After that, "rear front" susp hanger, rear bulhead and finally transmission. Feel super solid, i think i could adjust the infill for some weight savings.

Rear battery holder also ties up the aluminum body posts for more reinforcement/flex control:



The aluminum standoffs im using are these, in different lengths:

https://www.ebay.com/itm/224390616069?hash=item343eb91405:g:~b0AAOSwCy1gUsri

Edit: Here are some pics about first complete backend (minus rear bumper) rear motor assembly, with some frankenstein parts from SC6, RT5 and RB6.









Rock solid. Very happy with the results.

[HiTec]

Tested if its possible to fit sideways Shorty pack to this chassis. Its tight, because of the chassis profile, but possible. Ideally with this configuration you would want to use low profile (16mm height) 2S LiPo.



Dont know if i want this option to the final chassis or not. Because of the chassis profile, i have to raise the battery 4,5mm from the lowest point where the inlines bottom would sit against the chassis. I cant put it any lower, as otherwise the wouldnt be enough material on the chassis on the area where front side edges of the battery rest. Now theres like 1,2mm of material there (measured in the small area where the sideways battery eats away material the most). I also cant make that battery position adjustable in this chassis, without some serious re-design of the chassis bottom side. So with this its somehow "centered".

Edit: Added a picture taken from underside the chassis, where i highlighted where the battery sits with blue colour.

[HiTec]

Midmotor (Laydown) parts. Mainly rear laydown bulkhead and waterfall brace. This was easy (bulkhead still needs some final touches):



Managed to implement support for sideways battery with chassis integrated slot for the battery. Im honestly not a fan of how it looks, but i think its another good adjustment option so... Without foams, there is 7mm of free movement from rear to front with battery. Its not a lot in regards of adjustability, but thats the best i could do with this chassis. I still need to draw a battery holders for it, but those are easy as i can use the free body post points that the chassis already has. Thought that i will do a 2 sets of body posts. One set that ties up two points for flex control and one set that uses invidual holders for each post (more flex).

Also printed the front upper plate proto from PETG. Its crucial for front chassis flex control. Because i lost the "chassis wrapped aluminum posts" (because there is no room to wrap those aluminum posts with plastic, because the servo horn space is pretty tight), i needed to design the upper plate so it attaches to front bulkhead with 2 screws and to main chassis with 4 screws.

I tested the upper plate with installing just the bulkhead screws and the front chassis screws and it flexes too much. After installing those rear screws (that are also attached to aluminum posts, but are wrapped with plastic integrated to chassis), they eliminate the flex. So my gut feeling was right and this design should work nicely.

[HiTec]

Have been super busy this week, so not a lot of RC-stuff done.

Managed to design a motor plate for laydown. This one was pretty tight fit to do with 3D printing. With slipper eliminator, i could add more material to the motor plate, but with slipper the 3mm plate thickness is the thickest possible. The original SC6 aluminum plate is 2mm if i recall correctly.

I had to do some clever reinforcement to prevent motor plate from flexing under load. First one is integrated half cover for spur gear. And the second one is pairing up the motor plate to the same aluminum body post where the waterfall brace attaches. I know it isn´t 100% ideal to tie motor plate to that, cause it might change the flex on that side of the chassis, but that was the only thing i could do with limited space. Other option would be ditching the 3D-printed motor plate and use the aluminum. This design also means the if i want to swap motor and input axle around, another mirrored motor plate is needed.



Edit: Added couple more pictures:

[HiTec]

Just received the Team Orion 2S Shorty Pack (6200 Graphene LiPo, big thanks to hobbyfactory.fi for quick service!), so did a quick weight balance check with laydown and battery position maxed to front + Robitronic Razer Ten 4000kV motor. Test was done without ESC and Receiver and without rear bumper/battery holder (cause i havent printed them yet). The gearbox uses 4 gear configuration (because the 40T idler wasnt in stock): aluminum input shaft/gear, 26T SP idler, 26T aluminum idler and finally a gear diff.



Weight balance looks pretty nice to be honest. Also re-assembled my brand new Ultima ST Type-R EP and noticed that my chassis is actually stiffer than the original Type-R composite chassis. I havent checked the weights yet, so that might explain it. Anyways, here´s the front - rear weight balance pic:



The current state of the Service Pack is that if you own RT5 or SC/SC6, you can pretty much upgrade those to this updated design with re-using some of the parts from one of those cars and then just print the SP parts and buy a couple of cheap aluminum standoffs and assemble the car. I used RT5 susp parts for the test assembly in that latest picture + the SC6 rear shock tower (as i havent modeled the replacement yet).

Here is the front bulkhead with 15mm standoffs from ebay (for some reason, these light blue standoffs can be used directly with bearings without sanding. The dark blue inserts cannot). Top tip, you can use these same 15mm standoffs as a gearbox idler gear shafts, these are dirt cheap and even more lightweight than stock Kyosho):



From the underside (sorry for mixing screws, i dont have countersunk M3 hex/torx screws, local supplier was low on M3 screws):



In the first part designs that i did for Ultima ST, i had problems with front upper plate tearing itself off from the bulkhead, because the self tapping screws just ripped themself off from the PETG after some hours of driving in bumpy surface and crashing. I use my upgraded design in this chassis, that incorporates the heat pressed M3 inserts.

[silvertriple]

Looks really clean... Nice work!

[HiTec]

Thank you! I´m very pleased how this looks and feels so far. Cant wait to test drive it! Unfortunately i ordered wrong battery cable for this shorty pack (with 4mm connectors, when the battery has 5mm bullet connectors), so i cant test it until i find some 5mm bullet connectors somewhere.

[HiTec]

Quickly designed a rear wheel hub. Its a rough design as this will be the most problematic part for FDM printing, to make this durable. Stock geometry, but added some "beef" around it and also made it 2 piece. I didnt try to make it pretty at this stage. I just wanted to make a initial part i could test in this chassis.

The main part is printed with "virtual hinge pin" vertical at the print bed, because the hinge pin area really doesnt work if its printed in any other way. Except if theres a space to add one retainer screw for the hinge pin area, to tie up the print layers.

Edit: With that previous thought, i mean this design, that i used in the Type-R build:





Then the upper part, where the balljoint pairs, will be printed horizontally. These two pieces are then paired with three M3 screws.

I dont have any idea if this will work or not, i havent tested this kind of design earlier. But lets find out.

[USAPaulo]

Hi! New member just catching up with your work and it's incredible!

I'm an aircraft engineer and we're looking at additive manufactured (3D printed) components in all sorts of applications, including significant load-bearing structure. It's only a matter of time before this technology is available to mainstream users. In 10 years time it feels like printing your own parts (or getting a local shop to do it for you) will be fairly normal and will give you amazing flexibility with reduced transportation costs, etc...even more so than it already is! It would be great to see it reinvigorate the recovery of some of the vintage kits that original parts are no longer available for, it just needs the 3D models for the parts to be drawn.

Anyway, outstanding work, I look forward to seeing it continue to develop

Cheers, Paul

[HiTec]

Thank you USAPaulo for your feedback!

Im also eager to see how the consumer grade 3D printing is evolving when some years pass by. I've been thinking of buying resin printer for smaller/detailed parts, but the only thing thats holding me back is the durability of the parts. So im waiting for a better technology/resins for the consumers personal use.

I fixed some flaws from the first printed lay down motor plate and printed the second version with CF/PETG. (Adjusted motor screw locations for more space around the spur, made it more prettier, etc. Also added 1mm stripe of glow in the dark filament, as i really like how it looks.

This is at least as stiff as the alu plate. I cant get it to bend when its installed to the chassis with motor, so this should be good to go. The only thing that i kind of forgot was to beef up the plastic eylet that surrounds the 5mm aluminum body post. But that thin eylet isnt actually what prevents the motor plate from bending, as there is material on each side of the plate, that "leans" to the alu body post and chassis itself. I just need to be careful when installing the motor package to the chassis, so i dont brake the eylet (doesnt look good if its cracked). Im gonna fix this in the final version, but im not gonna print it, as this current version seems to be good for my personal use.

Anyways, some pics:

Motor/gearbox package, ready to be installed:



Also swapped those cheap aluminum standoffs to the gearbox:



Now the car waits for the final missing parts. Two 20mm/5mm aluminum body posts for front chassis upper plate and those 5mm bullet connectors for the chassis.

In a meantime i still need to print the rear bumper and design and print the front bumper. And also a midmotor compatible battery holder. First test drive is so close!

[HiTec]

First test drive done and it was a success!

Test setup was 2S shorty lipo, robitronic razer ten 4000kv motor, 60A ESC, 17t pinion, 4 gear laydown with gear diff + silicone oil (cannot remember what weight), stock RT5 front tires, JConcept pin downs in rear and main chassis without the flex adjuster plates.





3D printed parts: Front chassis lower plate, front bulhead, front inner steering arms, front upper plate, front shock tower, main chassis, battery holder, waterfall brace, motor mount, rear chassis plate, rear bulkhead. Everything else was stock RT5 and SC6.

This is the first time i was driving laydown and the amount of steering was overwhelming on this shitty low grip surface (tarmac/gravel).

Crashed/rolled it over it twice and still emptied the battery.

The only damage it suffered was that the stock RT5 rear shock either broke, or got loose. Overall, very happy with the test!

After the test:

[HiTec]

I'll be also making a Ultima SC upgrade chassis to SC6 style, so those with the old SC can upgrade to chassis that offers more adjustability with the different gearbox options as 1 gen SC owners are locked in to rear motor configuration with the stock chassis.

The plan for that upgrade is to swap back the RT5/RB5 style front chassis partion to ease up the upgrade (so first gen SC owners can reuse the the whole SC front end) and to lengthen the chassis by 40mm and offer stiffer chassis flex plates to deal with the possible flex, caused by longer chassis. Unfortunately i cant print that chassis, as its too long for my printer. But yea anyways, thats like 15 minutes of job to modify it to SC6 style with 1 gen SC front end, so why not?

[USAPaulo]

It looks great, it's going to be revolutionary to be able to make the changes at home, just like you're planning to do.

Fantastic work

[HiTec]

Thanks for the reply! Yea, i think so too. I could not find this scale of customization project posted anywhere, but im pretty sure someone has done something like this, just haven´t posted it anywhere.

I´ve done some small adjustments here and there. I added a small groove on the rear side of the chassis (both sides ofc) for the pinion swap. As for the easy spur gear change, theres nothing i can do for that with this chassis. I thought about making an removable rear side section of the chassis, but i ditched that idea for now, because its complicated and needs lots of full scale testing to confirm how it affects the flex and how much. I might get back to it later. So for now, with lay down configuration, the whole gearbox and motor packet needs to be partially removed from the chassis if spur change is needed. So it means that 4 screws from the top side (waterfall and rear bulkhead upper screws) and 4 screws from the underside of the chassis (gearbox screws) needs to be removed. This problem is only with the laydown configuration.



Also designed and printed the front bumper and the steering bellcrank middle link (with 3x7x3mm ball bearings).

Currently im working on a "easy-ish" solution for adding diff height adjustment for this chassis. Its not as fancy as some of the modern cars as the whole gearbox is moving up and down, but yea, i currently dont have enough time to make a custom gearbox and if i had, i would do it with quick diff access + diff height adjustment options. So the work in progress version includes some height shims, so you can move the gearbox up and down with or without the rear bulkhead + custom height adjustable rear shock tower, so you can move it with gearbox, or adjust it back to stock height so the gearbox height doesnt affect the rear shock tower height.