Alright the 21 has been out for a bit what is the feed back so far?
I have had a couple runs on the car now and it has very good turn in, the car really reminds me of the AX MMA. It is also very quite, my cars in general are pretty quite but this one is very very quite, and feels like it glides thru the corners.
On the build here are the things to look out for;
First, I never use the given link measurements in the guide as I put the final built car on a setup station. The steering lock makes setting the front end steering easy to do, its a nice touch.
Page 4 suggests filling the diff to 11.5 grams, not sure if my scale was messed up, but the empty diff came in at 13 grams so I just did the normal fill to the cross pin and called it good.
My only gripe was that those e-clips for the DJC and the CVD are very small and it would have been nice if they included a couple spares.
The 1mm claw spacers for under the lower suspension arms make it a lot easier to set roll center now.
Page 11, I ran into the spur gear being really close to the motor mount. I put a 0.02mm shim between the big bearing and the aluminum pulley to get the gear out just a bit. With that I also used a 0.02mm shim on the M3x4 screw that holds it all together. I also replaced the R9 c-clip with a external retaining clip, it just makes it easier to remove and replace gears this way.
Page 12, i used the 2 supplied 12x15x0.25 shims between the bearing and the excenter holder. I do this because the big side of the diff is really close to the bulkheads and could create drag.
Page 13, I use front upper arm in both the front and rear of the car, just a personal preference and no performance advantage, I do this as it give more material for the pivot ball assembly to screw in. I also replaced the M3x10 button head screws on the big side of the diff for M3x10 cap screws. The cap screws have a small diameter head which helps with the diff clearance.
Page 21, i used 0.01mm shims between the steering levers and the drag link on the M3x6 screws as without it felt like it had a bit of stick to it.
Page 26, build the shocks as normal, (I polished the shafts prior to assembly) but be wary of the amount of o-ring lube used as I had one shock that felt a little tighter than the other 3. It turned out to be just a little too much lube that when the lower cap was screwed on squished the o-ring enough to cause that drag. Cleaned out the little excess and the shock was perfect.
All in all the car built great, and there was no excessive trimming or filing required.
The car drives like it has great potential and time will tell.