Kyosho Ultima ST Type-R/Evolution GP custom gearbox covers for RB5 ball/gear diff and stock gears

thingiverse

Make Ultima ST great again... I created this custom gearbox, because i couldnt find original gearbox covers or the gears for the discontinued Ultima ST Type-R/Evolution chassis. This gearbox bolts to Type-R and Type-R Evolution chassis and its designed around easily to get Kyosho Ultima SC/DB/RB5/RT5 ball diff set (part nr. UMW602). I wanted to prolong the lifetime of this vintage chassis. You can also use the RB5 gear diff if you want, this is also fully compatible with it. The left side gearbox cover also has a small access hole for easy ball diff adjustments. Cover this hole with screw or piece of plastic when you drive the car, so you dont get dirt inside the diff. You probably need longer universal joints than the stock Ultima ST has, because RB5 output shafts are shorter than Ultima ST. This uses stock brake piston (6x5mm if i remember correctly), stock brake disc (30mm diameter) and stock brake pads. I used Inferno NEO/VE/MP7.5 brake disc, brackets and pads (last picture). Im not yet sure how long brake lever axle you need, because im fabricating my own custom axle from 4mm titanium. The brake shaft part that goes inside the gearbox is 20mm, the rest is what ever is needed for the part that sits on top of the gearbox. I suspect that the whole brake shaft needs to be 30mm long. I also created a ball bearing recess for the brake axle. That uses 4x8x3mm ball bearing. You dont probably need it, i can draw a plastic collar for people that dont want to use real bearing on that spot. Edit: Gearbox cover without bearing available in downloads. The idler axle needs to be exactly 16,8mm length. It is really tight fit with brake system. I did my own custom axle from 5mm titanium. I´m not exactly sure if RB5 input shaft works with this, because my car will use custom titanium input axle with aluminum 20T input gear (ARRMA AR310016 Idler Gear 20T). I left some space between the input shafts front bearing and the input gear to fiddle around with different gear styles. You need to shim it yourself with shim washers, depending what kind of input gear you use. I suspect that stock RB5 (UM524) main gear shaft should work, as i left so much space inside the main shaft bearing area, but i cannot confirm it, as i dont own the Kyosho main gear shaft. Please drop a comment if you are able to test it. I designed this to be compatible with Type-R/EVO style slipper clutches, but i can can confirm that also my Racing Sports version RS-153 slipper hub set works with this gearbox/brake system (just tested it). You can find it from the things I´ve created. I also have the brake disc in my shared designs. Bearings are stock RB5 bearings for the ball diff and for the idler. For the input shaft, you need 5x10x4mm bearings (standard wheel axle bearings, same bearings as idler gear has). The gearbox needs custom front support that is included in the set. I doubt that the Type-R/EVO version stock support works, because i created this from the scratch. I only used pictures i could find to create the support. I also suspect that we need custom upper brace. I will draw that some day and upload that also. Just be patient. Double check the installation depth on gearbox input shaft. You may need to shim it, so the spur gear hits dead center on the rear suspension arm slot (the groove on the arm). If the depth is not correct, its possible that main spur gear hits the rear suspension arm on full suspension compression. I printed my own covers with 100% infill, 0,2mm layer height and from CF/PETG filament. Clean the small flanges (the surfaces that overlap right and left gearbox halves) with hobby knife after printing, so the gearbox halves snap together nicely. And clean the brake piston and brake shaft holes with 6mm and 4mm drill bits. The left gearbox halves have 3mm holes for screws and right side gearbox cover has 2,5mm holes for 3mm screws to bite on. Depending on the filament you use, you might need to use 2,5mm drill bit to clean up the right side screw holes. The Ultima ST Racing Sports GP chassis plate "kind of works" (doesnt really) with this gearbox also, but this is really designed to be bolted straight to the Type-R or Type-R Evolution chassis plates. The center screw holes for the chassis plate are 0,5mm more further to the front in RS chassis (thanks Kyosho...) and ofc the front support holes are not where they need to be for RS chassis. The rear screw holes line up though. If there is interest, i can modify the design and upload Racing Sports chassis compatible version also. Give a comment if you are interested. EDIT: I uploaded the modified right side gearbox cover, without ball bearing brake shaft. Its the stock style version that Kyosho uses. This is for those who dont want to fiddle with extra ball bearings. Enjoy and drop a comment how did it work for you, or if you want any changes to be made! Also check my other parts that i have made to Ultima ST Racing Sports/Type-R/Evolution chassis. Here are the links to my project: https://www.rcuniverse.com/forum/rc-nitro-stadium-trucks-243/11675757-my-ultima-st-gp-type-r-evo-20th-anniversary-project-3d-printed-cf-parts.html https://www.rc10talk.com/viewtopic.php?f=30&t=44634