Optima Mid Runner (Almost Done, New Arms installed)

[bigjeepzz]

Big progress last week. I finally was able to machine the arms and get the remainder of the parts in to finish the build. I wanted to run the newer ZX5 wheels so i had to make a couple adjustments to the drawings on the arms. I ended up machining the front arms 1/4 wider then the factory ZXR arms, which made up the difference in the different wheel offset. I also ended up running 73mm swing shafts in the front and 62.5mm swing shafdts in the rear.

The factory Kyosho steering was cracked so I needed to figure out a way to make the car steer. After looking at the RC10 Worlds car steering I had at the house, I went ahead and machined new posts so i could have the ball bearing steering in this car. Works great but I am not getting full lock on the outside tire when turning. I may need to find some different bellcranks.

I fired the car up today and it runs really well. The B4 slipper works flawless and I am surprised how quiet this car runs. I need to take the car aprt and clean everything for the final assembly. There are a handful of things I am going to replace but nothing major. Will run the car with a boosted 13.5. If it doesn;t run like I want, I have an 8.5 which should be more than enough especially on the track I run on. Hopefully I can get to the track this week for some tuning. I may be able to get some video as well.

Parts Used:
ZX5 Wheels Front and Rear
ZX5 Rear Hubs
ZX5 Front steering arms and Castor Blocks
73mm Swing Shaft (Front)
62.5mm Swing Shafts (Rear)
RC10 Worlds ball Bearing Bell Cranks
Machined LIPO Cradles
Machined Arms
Machined Top Brace
LWB Chassis
SDPSI Belt
Repro Body and Undertray
Jake

[HKS_TRD]

Wow, that looks amazing! Where did you get the belt from?

[bigjeepzz]

Originally Posted by HKS_TRD

Wow, that looks amazing! Where did you get the belt from?

The belt is a true motion belt from SDP-SI. They pretty much have everything you could want from gears to pulleys, to belts.

https://sdp-si.com/eStore/PartDetail...7&GroupID=1022

127 Grooved belt is what I ordered. The only issue you will find is the belt width is 6mm. You must find a way to cut the belt. I made a jig on my lathe which made cutting the belt a breeze.

Jake

[HKS_TRD]

WOw interesting find

Sadly I don't really have a way to cut it so I will have to stick with the Kyosho belt

[bigjeepzz]

PM sent

[HKS_TRD]

Is that rear wing mount something you made yourself? I need something equivalent for one of my projects

[bigjeepzz]

I made some changes to the car since the last photos. The wing mount didn't work out the way I expected and I ended up machining a new wing mount from CF. Also the RC10 steering did not have the proper geometry and was not giving the front end full throw. I solved the problem by changing out the steering using an A&L setup. The car turns on a dime and is very controllable. I will be doing some track testing in korea with the car in the up coming months. It should be a decent contender in the current 1/10 4WD class.

Will update the pics very soon.

Jake

[Miggers]

Well nice.

I used to race a Mid Custom BITD and yes,they are quiet.

My racing team mate used to call it "The Hush Mobile",quite a revelation
after the Tamiya Boomerang's(my previous racer)screaming gearing.

It didn't want to slow down either,very little drag through the gearing
and belt.

[bigjeepzz]

I was able to get the car out to the Yongin Circuit in South Korea. I got to run a few laps with the Mid prior to a vintage race but put it away since I had to get my actual race buggy ready for qualifying. I was pretty happy with the car but it definitely need a bit of tuning.

2nd trip, I had full plans to race the Mid and showed up early to spend some time tuning the car. First two practice sessions went good and was able to get the car to respond properly. Third practice session, the car was running great. Got slightly out of control and hit the triple jump wrong. Crash ended my day by breaking the rear shock tower. due to me being in South Korea, I don't have access to the parts I need. I did not want to waste money on another OEM tower since it is definitely a problem. I am moving back to the US in one week so I will be machining a new shock towers from 5mm CF. That should fix my issues. Next trip to the track I will have video of the car running.

Jake

[mr. ed]

No more kim-chi for you soon he? I bet you won't miss the smell of that

I never understood why they made the shocktower of the mid in 2 parts. Maybe so you could replace the broken top part quicker

Personally I have a bit of mixed feelings over the mids: great looking cars and sturdy enough, good suspension with possibilities to upgrade easily (as you've shown well). But on the other hand; the lack of a slipper is so frustrating, and the mixture of belts and gear-on gear in 1 open gearbox is freightening.

I prefer the yokomo 870C design where you don't need to seal up the belt enitrely. I know the lazer has the same advantage, but somehow I can't get that car together and have it run smooth as the unsoiled mid transmission. So in the end they both sit half-assembled in boxes waiting for a new interest.

[HKS_TRD]

Great to hear you got her out for a bit of action
I couldn't tell from the pics but if you haven't already moving to a single piece rear tower will help alot in the strength department

Also, lazer rear towers bolt right up