Tamiya got it right all along

[Saito2]

I recently scored a slightly used RC10 Classic on fleabay for much cheaper than the original $250 NIB price (or shocking $399 second batch price). I wound up tearing it completely apart due to improper assembly and to see what makes it tick. The car really is a wonderful step forward in all respects except the transmission. Roger Curtis is a VERY smart man, but I don't know what the thought was behind the rather "different" original 6-gear trans. design. On the other hand, the Tamiya SRB's transmission design was actually to way to go, design-wise. While the rest of the SRB was archaic (in competition) at the time, the basic gear/drivetrain layout proved to be the same as the vaunted Stealth trans. Kinda funny when you think about it.

[WillyChang]

AE had a balldiff/spurgear in the RC12e which sat on the axle... I believe the original intention of the gearbox design was to reuse this balldiff/spurgear design in a buggy without compromising ground clearance, so it was raised high up. 

SRBs have no diff, neither did Kyosho Scorpion/Beetle originally 

[Saito2]

Being completely unfamiliar with on-road cars myself, the reuse of the RC12e design makes perfect sense. In the Winning Edge video, Roger Curtis mentions they tried some of their existing on-road shocks on prototype cars before discovering they'd need an all new design. It seems they were playing with parts they had on hand to see what would work.

11 hours ago, WillyChang said:

SRBs have no diff, neither did Kyosho Scorpion/Beetle originally 

While I know neither the SRBs nor Scorpion/Beetle had factory diffs of any kind, I simply meant the basic gear train layout (3 internal gears with external spur and pinion) of the SRBs wound up being the way to go from a design standpoint. Furthermore, the concept of a ball diff in the stock SRBs "spool" position was already reality as aftermarket companies were making diffs (gear and ball) for them by the time the RC10 hit the market. For these reasons I questioned the theory behind the RC10's use of a divided gear train using double the number of gears (and consequently, more possible drag).

[WillyChang]

Methink RC10's success comes more from being designed from ground up as a racer, not just repurposed toy. 6-gears might've dragged but wasn't much else on the market to compare to; RC10 was low slung with long wheelbase for track stability and it DIDN'T have trailing arm or chickenwing suspension 

You are right in that Curtis did a lot of novel innovations! We raced an RC300 and the stock kit didn't have a diff... wasn't much room left at spurgear after they've put in the disc brake system. Without diff it ran fine, as on the straight the rear wing downforce kept the rear end planted and in the corners the rear end loosened up as the rear tyres scrubbed.

The addon (supposedly torsen design) rear diff was a giant blob... and they placed it in middle of rear axle, least 2" away from the spurgear! Similar coaxial tube & shaft connection between the spur (+brake!) into diff before drive went to the wheels. Car still drove like before, but now you could put more power down coming out of corners  oooh loved overtaking nipping down the inside. Tyre wear reduced too.

It was a geared diff (like Avante!) so it's similarly interesting why they didn't choose this bulletproof design for RC10. Then again the RC12e was probably fresher in their minds and the idea of a screw-adjustable diff possibly more attractive.

 

[Saito2]

2" away from the spur? Wow that is different! I should take the time to investigate the vintage on-road stuff. Sounds interesting. Apart from the transmission, so much of the RC10 is simple, yet elegant. Its little wonder the buggy changed the face of off road. It lacks some of the overly complicated design motifs of the era and comes off like a competition weapon. Tamiya really didn't streamline their 2wd line up to match the RC10's general design-direction until the Madcap/Astute (even though the Astute was still overly complicated in some ways).

[WillyChang]

Well, this RC300:-

now fit this lump

[markbt73]

A properly set up six-gear RC10 gearbox will spin free for a few seconds, with no motor or dogbones attached, if you give the spur gear a good flick. Not much drag there.

I know what you mean about the SRB gearbox layout, though. Makes you wonder who was looking over whose shoulders in the early days...