Gearbox considerations for RWD Optima/Ultima project

[Coelacanth]

Once I'm finished with the Barney Optima, I'm going to build a custom RWD car using Optima chassis parts. I know many people did this back in the day, but I have a few questions nonetheless.

-I have several Optima rear gearboxes and a couple Ultima ones. What functional differences are there between the two? I would be using a hard final pinion gear if I went with the Optima 'box so other than that, is there any reason why one would use an Ultima 'box instead?

-What are some methods that were used to mount regular 2WD front wheels on Optima axles? I'd probably prefer to mount 12mm hex-style wheels on bearinged C-carriers rather than old-style wheels that have bearings housed inside.

Thanks!

[ROH73]

The gearboxes are functionally the same in terms of gearing, etc, but the Ultima gearbox does not have provisions for the rear A-arm hinge pins and it mounts flat to the chassis via holes on the bottom.

As for front wheels, Ultima 56mm (2.2") RB5 fronts have the hex in the wheel and are the correct offset, part number W5029W, http://www.kyoshoamerica.com/W5029W-Front-Wheel56-SizeWhite2Pcs_p_5157.html.

Matching rears are part number W5028W, but they're hard to find as they're discontinued.

[Mr. ED]

or you can get those nice meshed ones for the super-ten and cut the inner ring of the front ones

[highwayracer]

As stated, the internal and external gearing of the ultima and optima gearboxes are pretty much identical. The choice on what to use may bepend on the chassis you'll be using.

If you're using a flat sheet, then you can get rid of the optima plates and use the ultima box...since those have the mounting points on the bottom. If you do this, you'll probably wind up using the ultima rear bulkhead and pivot block. There are 2 versions of these parts.

The earlier version only has one set of mounting locations for the arms. The newer version (used on the ultima pro and newer versions) had 2 mounting points...which were used for longer arms. Stock ultima arms are shorter than stock optima arms.

[Mr. ED]

The hard pinion with its setscrew will not work on every ultima topshaft: some don't have the flat face for the setscrew, but that's easily ammended with a dremel. Another difference is the outer bearing for that top shaft. In the optima this bearing sits inside the gearbox, on the ultima it sits on the outside . therefor the ultima shaft is a little longer and has a groove for a large E-clips. To cut it short: if you want to go ultima gearbox , you also need to use the ultima topshaft and E-clips... unless you get a flaged bearing and enlarge the seating so it can sit on the inside.

Roger: have you ever tried using the inner holes in combination with the optima arms?
(shocks would have to go on the backside of the shocktower then.)
bzzz: I just remember those innerholes don't provide toe-in, and neither do the optima arms.

If you don't want to go all out and buy lots of new pieces: stick as close as possible to the optima parts. That's perfectly possible and reversible if you end up not liking it in the end. And if you still like it after you had a test-run you can gradually build it out further.

[Coelacanth]

Thanks for the responses, guys! I'm leaning towards using Optima parts because there's no real advantage (gear-wise) in using an Ultima gearbox, it would seem. I wouldn't want to use Ultima rear arms because I've already sourced out cheap aluminum GPM arms & Lazer hubs that fit nice and sweet and widen the track a tad.

The plan is to find a pan of some sort and mount the Optima's rear end onto it with cut-down frame rails. The front end will use an empty front gearbox as the front bulkhead. I hope to implement bell-crank steering and mount the battery longitudinally, and might lengthen the wheelbase.

As with all my builds thus far, the goal will be for it to perform well and look different. I'm only in the "imagine it" stage right now.

[highwayracer]

Marc, it sounds like you'll be using a similar setup as the hot trick conversions. You can easily fabricate some "L" brackets to mount the rear plates to the chassis...insteading of using the chassis rails.

Erik: I never tried using the optima arms on the newer ultima rear bulkhead (holes closer to the center) because the optima arms were too wide (front to rear). I'm currently going through this process with one of my ultima builds.

Regards,
Roger

[Coelacanth]

Thanks Roger...I'll stick with the chassis rails because I don't have swing-arms and want to use the alloy arms like I did with the CYANide & Barney cars. Those use hinge-pins inserted into the holes in the rails. I don't know why but I just prefer A-arms to swing arms.

[highwayracer]

That's right...I forgot about that. My orignal hot trick conversion used a-arms with the hot trick plates (which had an extra piece for the front mounting). The one I built a few years ago had the trailing arms...so I used the original plates...since the mount wasn't needed.

[Mr. ED]

Interesting spur you have on that h-t Roger.
Mark, Rogers suggestion would work just as well with the H-arms. Just use a hingepin mount like the one on the mid, lazer, lazer zx5 (?) between the plates. that will let you adjust the upward angle (camber?) too.

A disadavantage in your plan to use the optima gearbox and those side plates is: you loose a lot of space in front of the gearbox. Place which you need if you want to mount the battery lengthwise.

the ultima bulkhead makes you loose space too, but there's soutions like traxxas arm mounts

[Coelacanth]

A disadavantage in your plan to use the optima gearbox and those side plates is: you loose a lot of space in front of the gearbox. Place which you need if you want to mount the battery lengthwise.

I actually have that issue addressed...a battery can physically fit between the Optima's frame rails, and between the gearbox side-plates. The W-shaped spacer--which bolts to the upper deck and keeps the upper chain-guide in place--can be completely done away with for a RWD-only setup, and therefore won't be in the way either. Of course, I'm describing things as I picture them in my mind, and from test-fitting things with the Optimas I have now...mostly just theoretical.

[losiXXXman]

I'm also intrigued by your spur gear Highway. What is it, and or how did you adapt it... I have nearly enough parts for 3 Ultimas, but just one spur cluster. I have thought about making some sort of universal adapter to use standard spurs, but just haven't gotten motivated enough to do so yet.

[Coelacanth]

I'm thinking rather than fabricating L-shaped brackets (which would require 4 sets of nuts & bolts on either side), I'd just cut down some frame rails I already have, I have some that would be worthy donors as they're scuffed up already. The frame rails also accept the hinge-pins for the control arms, so I wouldn't need to modify anything that way, but could position the arms more outboard for a wider stance. Going that route, I would drill 2 holes through each rail (or at most 3) and bolt them down directly onto a pan or plate of some sort. That would eliminate the need for the excess weight of a pair of brackets & 2 to 3 sets of nuts & bolts.

What I'm wondering now is what would be a good pan or plate to use? Anybody have something that they'd recommend or aren't using? I believe I saw a possibility in a Duratrax one on Tower Hobbies a while ago...

[losiXXXman]

Marc the tower st15 chassis would take an ultima front end - bolt on... Then you can just cut off the rear tab and bolt on your optima rear. May want an upper deck, but its up to you. It is a 2.5mm chassis plate, but I've seen some bent up ones on ebay from the nitro abuse.

[Coelacanth]

Marc the tower st15 chassis would take an ultima front end - bolt on... Then you can just cut off the rear tab and bolt on your optima rear. May want an upper deck, but its up to you. It is a 2.5mm chassis plate, but I've seen some bent up ones on ebay from the nitro abuse.

Thanks, I was searching aluminum chassis' on Tower earlier this afternoon and that was one of the ones I saved to Favorites. I also like the Duratrax Nitro Evader ST chassis for it's simplicity...looks like an easier one to mod with a lack of screw-holes drilled everywhere and without larger areas removed making it complicated to custom-fit components from an Optima.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDSX2&P=7