Project OptiMutt - Finished

[longboardnj]

looking good i miss my optima mid, my dad made a cool off set (oval racing) fiberglass chassis (flat chassis make it easy to make your own chassis). years later i traded it with a friend that cut the chassis down to make it look like stock chassis. (bummer)

[Coelacanth]

Cool! With this Mid parts car, I received what appears to be a complete JG monster truck conversion set, I guess the original owner did that kind of build with this Turbo Mid SE. Body mounts & bumpers, Monster Beetle-style tires & chrome wheels in very good shape, axle extenders & wheel adapters from 12mm hex to Tamiya-style wheels...even a truck body.

[Coelacanth]

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Where dd you find those posts ?? possible to get an partnumber ???

Isobarik, I really had to Google hard to find that info...I thought they were Tamiya parts, but they're actually Duratrax Raze parts. I usually keep all the header cards for all the parts that end up on my cars, but that's the thing...those didn't go on either Barney or CYANide so I must've tossed out the card!

Here's a link:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMKH7&P=7

[Coelacanth]

I had a free day this Saturday so here are more progress pics. Sealed the rear gearbox and installed the wing mount. I then fabricated a carbon fiber front shock tower and installed the empty front gearbox and stabilizer wire. Now I just need to wait for some front arms to arrive from a fellow forum member before I can do anything more.

[Hcp22]

Coming along nicely...

[Coelacanth]

I have something really cool planned for the electrics installation...wasn't quite finished the planning last night, but got some soldering done and the servo & saver mounted and a turnbuckle ready to connect to the bellcrank...this is gonna be smooooth. And wait until you see how I'm planning to mount the ESC! I had originally wanted to mount the battery longitudinally to move some weight forward and lower the center of gravity, but had to scrap that idea as there just wasn't enough room...pics at 11:00.

[Coelacanth]

I installed a nice blue aluminum servo horn with a Tamiya high-torque servo saver, as the bellcrank doesn't have one. The stock Optima/Mid steering linkage is functional but there are numerous metal-on-metal friction points and rather weak ball joints. This aftermarket bellcrank with bearings looks to be solid as a rock and smooth as silk, with no slop whatsoever. I can't wait to try it out once I've installed a receiver. I used some random Associated titanium turnbuckle and 4.8mm balls/cups to connect the servo with the crank.

I chose the Leopard 12T 3300kv motor/ESC/program card combo for OptiMutt...yeah, a big reason was because it was orange, which is as close to gold as I could get.

As I mentioned the post before, I originally wanted to mount a battery longitudinally but no matter how much I stared at it, I just couldn't find a way to make it fit without completely cutting up the chassis and adding on a chassis extension piece, or buying an expensive carbon fiber or graphite chassis plate.

I was thinking about the best way to install the ESC when it suddenly occurred to me--the ESC was almost as wide as the space between the upper/lower deck! I did a few test fits and found there was JUST enough room to sandwich the ESC sideways between the decks, with the fan outward so as to receive some airflow, and enough room not to obstruct the steering servo. With the ESC mounted there, it's super neat & slick, lowers the center of gravity considerably, and also allowed me to move the balance point more forward.

I used a Dremel to open up a sort of keyhole shape in the top deck that I could route the ESC motor wires through. Here's a preliminary fit. I've attached the ESC to the underside of the top deck with double-sided tape and will clean up the wiring with zip-ties once all the electrics have been tested. I'll use Velcro instead of double-sided tape on the bottom of the ESC where it mates with the bottom deck, so I can easily remove the top deck when necessary.

Have you ever seen an Optima or Mid that looked anything like this?

[Coelacanth]

Unfortunately I don't have picture updates, I'm saving it for when I finally get some front arms & steering components shipped, installed & working properly, but I'm getting excited about this build! I got the radio & ESC basic functions working, steering servo & bellcrank is zeroed in and works fantastic. I streamlined and tidied up my wiring, this car is looking very sleek! I'll share some tips & tricks soon.

I have a couple questions: Has anybody bought a motor & ESC combo where the 3 colored wires actually connect to the same-colored wires?? Practically every ESC & motor I've connected was in reverse rotation when I connected the yellow, orange & blue wires to their matching counterparts! I've had to switch a pair of wires on every one of my cars, and it just looks dumb.

Second question is regarding the gear ratio and pinion gear mesh. I was aiming for something between 4:1 to 4.6:1 ratio of pinion:spur; I'm currently trying a 78T spur and have 16T and 18T pinions. Note that the spur/pinions are 48-pitch, I believe (I have a selection of Robinson Racing spurs to choose from, 75T, 78T and higher). Anyway, with either of the pinions, the Litesink motor mounting holes don't permit the motor to be moved close enough to get the pinions to mesh properly with the spur. Should I be using a significantly larger pinion, or will I need to mod the motor plate by extending the holes with a Dremel or drill? What do you guys with modernized Mids recommend?

[Mr. ED]

The 0.6 module standard spur has 74 teeth and is considerably larger than a 75 teeth 48pitch spur.

Measure the diamter of the stock spur and get a similar diameter spur in 48p. Extending the slot holes won't help: your motor is probably already almost touching the transmission case.

[Coelacanth]

The 0.6 module standard spur has 74 teeth and is considerably larger than a 75 teeth 48pitch spur.

Measure the diamter of the stock spur and get a similar diameter spur in 48p. Extending the slot holes won't help: your motor is probably already almost touching the transmission case.

Thanks for the tips, Mr. ED. Actually, the 78T spur was one of the smallest of the Robinson Racing spurs I received in this parts lot. Some of the bigger ones wouldn't even fit inside the stock gearbox cover. Good point about the motor touching the tranny case, I'll have to check that out. At least there's no belt guide covers to get in the way, I just sealed off the holes where the belt would've gone through.

[Coelacanth]

I don't have much to update as I'm waiting for some arms & random aluminum parts to arrive, but I spent some time tidying up the electrics installation. I also had to upsize my spur & pinion gears as the 78T spur & 17T pinions weren't able to position close enough to mesh properly. I had to search for appropriate pinion gears, I was only able to find two that are compatible with the white Robinson Racing spurs, a 16T and 18T, and chose the 85T spur, for a ratio of about 4.72--a bit higher than I was aiming for, but I'll see how it works with that combo before buying other pinions.

[Coelacanth]

Had some spare time last night and since I'm getting bored sitting on my hands waiting for some parts to arrive, figured I had to do something constructive. I had some leftover carbon fiber lying around so I made some carbon fiber suspension pin plates. I'm getting tired of looking at this thing without a front end.

[Hcp22]

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Hmm, I don’t know if like that black tubing… I think this would look nicer…
http://www.ebay.com/itm/Braided-Hose-and-Wire-Sleeve-Whole-Engine-set-w-Heat-Shrink-41-Ft-w-Rad-Sleeve-/171016848732?pt=Motors_Car_Truck_Parts_Accessories&hash=item27d166055c&vxp=mtr

[Coelacanth]

Hmm, I don’t know if like that black tubing… I think this would look nicer…
http://www.ebay.com/itm/Braided-Hose-and-Wire-Sleeve-Whole-Engine-set-w-Heat-Shrink-41-Ft-w-Rad-Sleeve-/171016848732?pt=Motors_Car_Truck_Parts_Accessories&hash=item27d166055c&vxp=mtr

LOL Guess what, I tried that first! I had a bunch of black braided sheathing, I've used it in the past with modded computers...but it looked like ass when I was done and doesn't protect from stray water droplets either. The problems with braided sheathing is you have to cut the ends and they ALWAYS fray, even if you pre-heat the ends with a flame. It can also be a pain to install over larger areas like where the 3 motor plugs connect to the ESC; this resulted in me having to use a braid larger than I wanted, and it just got too bulky-looking. Lastly, with braided sheathing, you can't easily slip your wires out at any time to check or change connectors, for example...which is not a good thing if you're still in the planning stage of a build.

Needless to say, I ripped out the braided sheathing and went with plastic split-loom. It's so much easier to work with, protects better, and looks good.

Based on my experiences with it, I don't recommend braided sheathing--at least for RC cars. Works great for modded computers, though.

[Hcp22]

Who cares if it’s practical, it’s all about appearance my friend…