Project OptiMutt - Finished

[Coelacanth]

Here are some early pics of a new project I'm working on. I don't have a RWD RC car yet, and tons of spare parts for the 4WD Optima...so what to do? Well, I bought a couple parts cars and spare parts from flipwils11 that included 2 mostly complete Optimas and what turned out to be a nearly complete Turbo Optima Mid SE which was mostly in parts. It wasn't until many months later when picking through all the parts and parts bags that I discovered I had almost all the parts needed to build the Mid SE. However, I didn't want another 4WD, I wanted to build something different (as usual).

The idea of a mid-motored RWD car intrigued me, so I thought about how to do this. I spent 3 or 4 months just figuring out what I had that could contribute to the build, and a lot of research on how to make it solid as a rock. I'm fond of aluminum (of course) so alloy parts would be an important characteristic. I don't have the spare dough to de- and re-anodize everything in funky custom colors, so I'm going with a mostly blue & gold theme.

This build will use parts from GPM, Tamiya, Yeah Racing and Kyosho (of course), and probably more to be determined. So far, it's looking pretty good!

[SFC K]

That looks really nice. The blue and gold complement each other nicely. That is also one heck of a heat sink on there. Looks cool so far!

[j0pp3]

Very inspiring project!

One great thing about 2WD is the possibility of elaborating with wheelbase without the need for adapting the drive line. Who will build the first Optimister (Optima Mid Dragster)?

Just a question of curiosity; which Kyosho vintage models have a 2WD front that's designed for a none kickup chassis? I can only think of one right now and that's the Triumph...

Cheers

[HKS_TRD]

Which rear arms and bellcranks are those?

Where do you get stuff anodised, I have some Optima Mid chassis posts I want to get done in blue and a pair in gold, and a Lazer ZX motor brace I want to get done in blue but no one here will do small parts

[Coelacanth]

Very inspiring project!

One great thing about 2WD is the possibility of elaborating with wheelbase without the need for adapting the drive line.

I was REALLY hoping to be able to do this, my goal was to mount a battery longitudinally...but without cutting up the bottom plate, I just didn't think it was feasible. It would seem easy at a glance (I initially thought so) but the more closely I looked at it, the more of a challenge it evidently was. If you could just relocate the rear gearbox on a longer chassis plate, it would indeed be easy. The plastic piece that mounts to the motor plate and separates the motor from the battery ahead of it, needs to be installed as it braces the whole front of the rear gearbox. Another issue is the space just ahead of where the motor would be isn't wide enough to allow a standard-width LiPo battery to lay flat. Other complications would arise from the rear gearbox relocation such as affecting the top deck; the aluminum spanners would also need relocating and the front of the top deck won't mount to the front half of the car if it was relocated an inch or more rearward...

I really wanted to make a longer wheelbase work...I'm certainly not saying it's impossible, but it's a lot more re-engineering than I was prepared to do and more difficult than it would at first seem. Of course, if I could afford a bunch of 3mm carbon fiber, I'd be able to fabricate my own decks.

[Coelacanth]

Which rear arms and bellcranks are those?

Where do you get stuff anodised, I have some Optima Mid chassis posts I want to get done in blue and a pair in gold, and a Lazer ZX motor brace I want to get done in blue but no one here will do small parts

The rear arms are made by GPM for the Tamiya DF-02. I've used these arms with both my CYANide and Barney custom Optima builds. They work almost perfectly as a swap for the regular Turbo Optima arms but are ~5mm longer, so you'll need 68mm Kyosho Lazer CVDs instead of 62.5mm stock Optima units, all else being the same.

http://www.ebay.ca/itm/ALUMINUM-REAR-LOWER-SUSPENSION-ARM-B-TAMIYA-DF-02-DF02-/400414695336?pt=US_Character_Radio_Control_Toys&hash=item5d3a935fa8

The bellcrank is Tamiya #54235 for the FF-03.

http://www.ebay.ca/itm/Tamiya-54235-RC-FF-03-Aluminum-Racing-Steering-/230825007019?pt=US_Character_Radio_Control_Toys&hash=item35be3e17ab

[Mr. ED]

Just a question of curiosity; which Kyosho vintage models have a 2WD front that's designed for a none kickup chassis? I can only think of one right now and that's the Triumph...

Cheers

pro-x , ultima RB (and RB5)

[Coelacanth]

By non-kickup chassis, are you gents referring to the chassis plate being completely straight, as opposed to most other RWD chassis plates having an angled front section, where the front control arms & shock bulkheads are mounted? I've considered giving the front section of this plate a similar bend, as it wouldn't seem to affect the mounting of the control arms (they use e-clips on either end). I assume this would provide more aggressive turning characteristics?

[Mr. ED]

All of those models have a flat chassis, but they also have a nose plate attached to it: which provides anywhere between 20 and 30°s to the front arms.
I don't know the exact reason but if I'd had to guess I'd say it is to receive the bumps better and prevent the lighter nose from going up in the air

You 'll need a narrow front bulkhead to match the narrow mounts of the rear : something like the triumph.
(I've been looking at a similar build but never got quite round it... and now the ultima is running so well, I have no need for another 2WD runner)

[Coelacanth]

All of those models have a flat chassis, but they also have a nose plate attached to it: which provides anywhere between 20 and 30°s to the front arms.
I don't know the exact reason but if I'd had to guess I'd say it is to receive the bumps better and prevent the lighter nose from going up in the air

Thanks Mr. ED. I was kind of wondering, with the motor being mounted in the middle instead of out back, if that might also help with that...I guess only time will tell. What I've read is that RWD cars seem to work better with some track conditions having the motor in the rear. I guess when building something like this, you never know how it'll handle until it's finished.

[losiXXXman]

Cool new build Marc! I'll be interested in how the front end pans out. I'd be inclined to put a bend in it up there, I think any 2wd is going to be little bit of a pig without some kickup and caster. I think the raider only had 10 or 15, and mine didn't turn for crap. Of course the stock front treads were'nt helping much either.

[j0pp3]

All of those models have a flat chassis, but they also have a nose plate attached to it: which provides anywhere between 20 and 30°s to the front arms.
I don't know the exact reason but if I'd had to guess I'd say it is to receive the bumps better and prevent the lighter nose from going up in the air

Thanks Mr. ED. I was kind of wondering, with the motor being mounted in the middle instead of out back, if that might also help with that...I guess only time will tell. What I've read is that RWD cars seem to work better with some track conditions having the motor in the rear. I guess when building something like this, you never know how it'll handle until it's finished.

For RWD cars: On loose tracks you want more weight on the rear wheels (rear mounted motor) to get good traction. For high bite tracks like astro-turf or similar you want a balanced weight (mid motor) as traction isn't a problem. A balanced weight make the car more calm and can be pushed a bit harder.

[j0pp3]

By the way... Your have inspired me to craft a chassis that's a hybrid between an LWB Mid (rear) and a Triumph (front) with the servo placed to fit the Triumph steering geometry. Thank you Coelacanth!

[Coelacanth]

You're welcome, j0pp3.

Since I won't be running 4WD with this Mutt, and will be needing the front gearbox to mount the shock towers and other front end stuff, I wanted to seal the unnecessary holes...I just figured I didn't want clumps of dirt to end up trapped inside the gearbox, even though there's no diff in there.

I found some random pieces of chromed steel with a perfect fit for where the diff bearings go, cut it into 2 disks, and ground them down so they were quite thin--to keep weight down. I've seen some people just pour gobs of epoxy inside a diff they wanted to seal, but that would add a lot of unnecessary weight and looks like crap. So, a few dabs of 5-minute epoxy and in went the disks.

I then had to seal off the 2 rectangular holes where the belt feeds into the front diff. One issue I noticed was that the bottom standoffs for where the lower belt cover attaches got in the way of my Tamiya steering bellcrank, so I removed both top & bottom standoffs and shaved them nice and flush with an X-Acto knife. To seal off the holes, I had a sample piece of 1mm carbon fiber that was big enough to cut into 2 pieces...and how cool does that look?

[isobarik]

Does the bellcrank differ much from the original part ???

mvh Isobarik