Turbo Optima build - Project Barney: Finished

[Coelacanth]

Once I got things assembled up to this point, an annoying problem appeared--whenever I'd compress the front suspension, the wheels would toe-out quite significantly...the dreaded bump-steer! I don't want Barney to handle like a truggy so I began researching ways to resolve this. Neither of my other 2 cars--CYANide and the Zebra Optima--had bump-steer, their suspension was practically perfect, so I was a bit perplexed what was causing it. The only parts that weren't direct replacements of a stock part were the GPM Lazer C-carriers. Looking at the steering knuckles from the side view showed me that Barney's knuckles were more horizontal, while the other Optimas had a significant angle.

That gave me the idea to try a fix that was surprisingly easy. I kept reading that bump-steer is often caused when the tie-rods aren't parallel with the control arms, and that was indeed the case with Barney's steering setup. I simply added a 4.8mm ball-end to the opposite side of each steering knuckle, keeping the original ball-studs there in case I ever need to change my configuration, and popped the ball-cups onto the balls underneath. Now, the rods were almost perfectly parallel with the arms...and the bump-steer toe-out was completely eliminated. I now have a slight toe-in which I hope will perform well. Certainly better than it was before.

[Coelacanth]

I finished fabricating the servo mount today. I made it from some Axial 3mm x 6mm threaded posts, cut into 4 pieces approximately 5.3mm long. Like I did with the CYANide car, I cut out a Lexan chain-guide dust cover of sorts. Reaming out 4 holes and having them line up with the fabricated servo mount, and then with the Optima top deck's holes, was finicky work. I Goop'd the chain-guide cover on, let it dry overnight and today, cut down four stainless steel 3mm screws to between 5 - 5.3mm, just long enough to thread into the green spacers by a good 4 full turns--but not enough to butt against the flat-head 3mm screws underneath. Cutting the top & bottom sets of 4 screws was probably the most time-consuming and boring task. Cut them too short and they won't thread in enough; cut them too long and they'll hit the opposite screws already threaded in.

I also had to file down one pair of posts to get the servo mount to fit snugly, as the stock plastic part also has those areas flattened.

But, after all was said and done, it turned out great. Thanks again to Jay Dub for the suggestion to use threaded posts instead of spacers, so I didn't have to use ugly nuts on the top.

[Coelacanth]

The green springs I managed to track down for Barney were *almost* perfect. They were the correct diameter (I wanted them slightly larger diameter than stock Kyosho Gold shock springs to beef up and smooth out the suspension) and turned out to have a nice degree of stiffness. I want this car to ride smoothly but not bottom out for anything but the biggest bumps.

There was only one problem that I figured would be minor, but turned out to be quite a complex issue to resolve. The springs (out of the bag) were much longer than necessary. Oh well, I figured I'd just cut them down to size and be done with it. The problem this created was that the cut spring ends wouldn't lay flat on the bottom spring cups, which caused the springs to bulge out at one side, and which became more pronounced as the shocks were compressed--which also allowed the springs to contact the shock bodies and rub there. (Excuse the so-so quality of the cell phone pics, I've temporarily misplaced my camera.)

SpringMod1.jpg (17.78 KiB) Viewed 1985 times

SpringMod1.jpg (17.78 KiB) Viewed 1985 times

Pic showing spring bulge:

I then figured I could just whip out a few needle-nose pliers and give the cut ends a few bends to straighten them out--but this just mangled and distorted the 2 spring ends I tried this on, and made a mess of things.

After thinking it over a while, I figured out what I think is a pretty good solution. I picked up some 3/32" copper tubing at the LHS and a small pipe bender. I wrapped the pipe around something approximating the diameter of the springs and cut off about 5 or 6 copper "sleeve rings". I filed down the cut edges and gently bent them in such a way to be close to the original springs' shape. I then cut off 4 ends of the opposite ends of the previously-cut-down springs, keeping the parts that have the "flats". (Wish I could describe it better, but the pics will show what I mean.)

I then shoved both ends of each spring set--the long original piece and the short end piece with the flat end--into the 4 best copper sleeve rings. With a bit of final bending and tweaking, I got both ends of the springs to lay flat. I then gave each sleeve ring 4 firm crimps with a side cutter to keep everything in place. Since each end of the spring is shoved in a full half-circle, I doubt they're going anywhere--even without the crimps.

SpringMod2.jpg (13.66 KiB) Viewed 1985 times

SpringMod2.jpg (13.66 KiB) Viewed 1985 times

The end result was just what I was hoping for--almost all the spring bulge was eliminated, and there's no spring/shock body contact even with full shock compression!

Now that Barney has all the electronics installed & calibrated, I'm just about done the chassis...and it's time to get a body trimmed and painted soon.

[Mad Racer]

Looks good Marc.

Is this a runner or Show Pony????

Is that my old belt drive conversion or another one??

Cheers

Mark.

[Coelacanth]

Barney will definitely be a runner! Same with CYANide. I don't really believe in shelf-queens. I certainly wouldn't go to all this trouble focusing on suspension and performance-related details, or install electronics and stuff, for a shelf-queen.

I think your belt drive parts went into CYANide...for Barney, I pretty much did my own conversion from parts I already had...I had a new SG-25 sprocket set, a few Optima Mid belt diffs, I think your belt, I used rear gearbox halves that already had the parts modified, and made my own Lexan dust-cover. Another forum member provided the little idler gear & shafts.

[8rad]

A+ for thinking outside the box Coel. Now you just need to wait 20 years for the copper to turn green!

[Coelacanth]

A+ for thinking outside the box Coel. Now you just need to wait 20 years for the copper to turn green!

I'll have the first RC car with a patina!

I could've gone with either brass or aluminum...but aluminum tubing was too soft. For some reason, I liked the copper look more than brass...

[Coelacanth]

Here's a couple shots with the electronics installed. Motor is a Tacon 3650 11T, 3200 kV unit and a Bullistorm 60A ESC. FlySky GT3B radio & receiver with digital metal gear servo. (I gotta replace that blue AE turnbuckle with a purple one, but I didn't have any on hand in a length that would work...but soon!)

The fan on the Bullistorm heatsink is a piece of crap. The fan blades wouldn't even spin freely. You can easily distort the fan housing with a little finger-press. I removed it & threw it in the garbage, replacing it with a same-sized Novak fan. That fan is so smooth and quiet, even compared to my buddy's EZRun ESC's, which make an irritating high-pitched whine.

I tried to minimize cabling as much as possible (cutting down the wires and reattaching the connector ends, except for the motor, you're not supposed to touch those wires). Hopefully it's pretty neat & tidy for an offroad buggy...what do you guys think?

[RedScampi]

That's quite a beast you put together there Marc. You've been very resourceful throughout the build. I am interested to see what body and paint will look like.

[Coelacanth]

I chanced upon this eBay auction and was surprised there was no bidding activity through to the end time, and threw in a low bid. Now Barney will have the perfect wing buttons! The price was right, anyway.

http://www.ebay.ca/itm/370582179602?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

[Goatless]

All I can say is WOW! Great ages of build there! Gorgeous ride thee Coel!

[Coelacanth]

All I can say is WOW! Great ages of build there! Gorgeous ride thee Coel!

Thanks Goatless! I'm currently vacationing in Mexico, but when I return, it'll be time to plan out the body. I only hope it turns out as good as the chassis did!

[Hcp22]

Sir! When do you plan to show us the chassis together with the body?

[Coelacanth]

Sir! When do you plan to show us the chassis together with the body?

When I get around to trimming & painting the body. Maybe in a few weeks...I've got a lot going on at the moment and can't seem to find much time to work on RC stuff. At least tonight, I removed the ugly blue AE turnbuckle that I was using temporarily for the steering servo and replaced it with a nice purple titanium Schumacher unit, and got all 4 wheels mounted with black HPI 4x14x1.5mm washers, so all you see now are the green lock-nuts--no more silver alloy spacers.

[Mad Racer]

Marc .

What steering servo is that??

Purple label. I think a KO ??

Gee you go to alot of trouble to stick with your theme. Great effort.