Porsche 911 with bespoke chassis

[IXLR8]

I’ve wanted to add a Porsche 911 to my growing collection of on-road RC’s for a while and the time would have been perfect when Tamiya released the 45^th Anniversary edition 934 in late 2021 but for whatever reason I missed the opportunity to order a copy; maybe it wasn’t on my radar at the time or I was head-deep in other projects – not sure.  Anyway, production for the anniversary model was limited, most were quickly scooped-up by collectors and what remains appear on ebay and similar websites with absolutely insane prices well outside my budget.  Also, there’s a small issue I have with that model’s supplied chassis and I’ll get into that in a moment.

With the 45^th out of reach, my second choice is Tamiya’s Porsche Carrera RSR:

 

That car looks great and would serve my purpose very well -- except for the supplied TT-02 chassis.  Actually, the TT-02 chassis is fine (I have the 1999 Subaru Impreza rally car on that chassis and it goes very well) but the TT-02 is mid motor and AWD and Porsche 911’s from that era were rear motor and RWD.  Unfortunately for me, the 45^th Anniversary model is on the TA02SW chassis which is also mid motor and AWD.  Again, the TA02 is a great chassis but I’m after something with a bit more scale accuracy.

I wanted to move forward anyway so a few months back I purchased Tamiya’s Porsche RSR body set and began to search for a more appropriate chassis.   I’m an AE fan from the 1980’s so my first thought was to assemble an RC10 Dual Sport but parts availability and prices can be a problem for that chassis so I really needed to look for alternatives.  Also, there’s another consideration that I forgot to mention – the Porsche’s trailing arm rear suspension.  There aren’t many readily available on-road rear motor RWD RC chassis’ and none that I’ve seen also feature trailing arms.  I guess I could modify a Kyosho Scorpion for on-road duty (it uses trailing arms front and rear) but it’s metal and very heavy so eventually I decided to design and build a chassis specifically for the Porsche that captures all four features; rear motor, RWD, trailing arm rear suspension and reasonable cost.  I’ve designed and built RC chassis in the past.  I really enjoy the design and fabrication process and the opportunity to gain a better understanding of suspension and steering geometry that comes with custom builds. 

I’ll show the design in the next post.

[IXLR8]

So, after many hours spent researching, selecting parts and refining the design, here’s what I intend to build.

I’ll run through the parts list and dive into the details in my next post.

[Kowalski86]

2 hours ago, IXLR8 said:

There aren’t many readily available on-road rear motor RWD RC chassis’ and none that I’ve seen also feature trailing arms.  

You could go with something out of left field and use an ORV chassis. They're rear motor RWD, trailing arm suspension, parts are everywhere, and the wheelbase is about 251mm.

[IXLR8]

2 minutes ago, Kowalski86 said:

You could go with something out of left field and use an ORV chassis. They're rear motor RWD, trailing arm suspension, parts are everywhere, and the wheelbase is about 251mm.

That's an OUTSTANDING suggestion - the ORV ticks all the boxes.  I just built a Blackfoot and it never occurred to me that chassis could be used for my Porsche build.

However, I'm already so deep into this that I can't turn back now.  Hopefully, my chassis will have a lower CG than the ORV - or at least that's the excuse I'll use to justify continuing down this path.    Honestly, I just like making stuff.    

[Kowalski86]

17 minutes ago, IXLR8 said:

That's an OUTSTANDING suggestion - the ORV ticks all the boxes.  I just built a Blackfoot and it never occurred to me that chassis could be used for my Porsche build.

However, I'm already so deep into this that I can't turn back now.  Hopefully, my chassis will have a lower CG than the ORV - or at least that's the excuse I'll use to justify continuing down this path.    Honestly, I just like making stuff.    

Thanks! I used it for my own baja bug project in part because of the trailing arm suspension.

I'm hoping that your chassis will have a better transmission than the ORV, and a means of mounting actual front shocks.

[IXLR8]

Yes, there’s definitely provision for front shocks but the transmission – well, that remains to be seen. 

 

For shop fabricated parts, the main chassis will be aluminum 6061-T6 (0.090”), shock plates and rear body mounting plate will be G10 (0.090”) and remaining plates G10 (0.060”).  I have some Kydex for the front bumper.  I’ve built other chassis using 6061 (0.090”) and I believe that material will be sufficiently rigid for this application.  However, if the amount of flex proves to be unacceptably high, I can add a full-length top plate that will effectively link the front and rear shock towers and increase rigidity.  I know it defies logic but sometimes a car with a tiny bit of chassis flex is easier to drive fast.

For the bar parts, I have a small lathe so I’ll turn the rear trailing arm mounts, rear upper shock mounts and rear shock plate mounts from aluminum bar.  The battery post and rear links will also come from aluminum bar as will the various required spacers and stand-offs, front camber and steering links.  I have most of these materials on-hand – remnants from past builds.  I’ll also need to turn the front axles as the ones I have won’t fit the Tamiya wheels.  I’ll make the axles from mild steel.

The front and rear suspension arms and front bulkhead will be printed from sintered nylon (a.k.a. “Polyamide”).  These parts have been ordered.

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For sourced parts, the caster and steering blocks are Associated SC10 parts (7919 and 9880), shocks are Tamiya CVA Mini’s (I chose plastic bodied shocks to save weight), the steering rack assembly is Traxxas 4-Tec (8343), the universal half-shafts and hex drives are Traxxas E-Revo (7151 and 7154).

For the transmission (and here’s where this could become a bit controversial), I chose an Austar 3-gear crawler transmission.  WHAT, a “crawler” transmission in a Porsche?!?!  Yup, this tranny runs well (I have them in three of my trail trucks), it’s light, inexpensive and includes ball bearings and a slipper clutch - however it doesn’t include a diff and I don’t believe one is available.  Now, I’ve owned an RC before that didn’t have a diff; I bought a Sand Scorcher back in 1979 that was converted to run dirt oval in the mid 1980’s and it performed very poorly (tremendous oversteer on corner entry).  I believe most of the handling problems with that car were due to it having a locked rear axle.  I’ve never ran an on-road car with a locked axle so I guess we shall see.  I could be wrong but I think early RC500's didn't use a diff.  Anyway, if it becomes a serious problem, before looking for a replacement gear box with a diff, I may have solution in mind.  It might be possible to design and print a final gear that will accept the differential set from – you guessed it – a Traxxas E-Revo.  I believe this bevel gear set is small enough to fit into a 52t final gear but I’ll cross that bridge if I come to it.

 

The front camber link and steering ball studs are from Custom Works (8121 and 8122) and ball cups are RPM (73372).  The rod ends for the rear radius arms are M3 aluminum pieces that I purchased from an ebay seller.  When these arrived, the ball fit was very loose but I've found that they can be tightened by pressing the bronze insert slightly deeper into the aluminum housing.  I’m paying a weight penalty here but if rear traction is very high, corner loads on these links could cause a plastic rod end to flex and this would alter rear camber and possibly even the toe angle so I wanted the added rigidity of aluminum on these links.  Plus, I like the shiny anodized finish.  

 

Speaking of rear toe angle, each washer removed increases toe angle by about 1 degree and camber angle can be increased by adding washers to the lower radius arm.  This design has both set to zero angle.

 

Okay, more to follow....

[ThunderDragonCy]

This is excellent. Looking forward to seeing more. 

[GermanTA03Guy]

Great stuff !!! Only shame is that the rwd rc cars always only have rear brakes.... theoretically, a 4wd Belt with a one way inserted the other way round could solve this. But i think youre too far for that and its 😎 like it is 

[ChrisRx718]

That's a lot of work so far!

But the easy option would have surely been M-06, TL-01 suspension arms and dogbones and a bespoke spacer... Rear motor/rwd.

[IXLR8]

12 hours ago, GermanTA03Guy said:

Great stuff !!! Only shame is that the rwd rc cars always only have rear brakes.... theoretically, a 4wd Belt with a one way inserted the other way round could solve this. But i think youre too far for that and its 😎 like it is 

Yeah, it’s a compromise; AWD and better braking or RWD and better scale accuracy. 

Honestly, who needs brakes anyway, they just slow you down. 

[IXLR8]

11 hours ago, ChrisRx718 said:

That's a lot of work so far!

But the easy option would have surely been M-06, TL-01 suspension arms and dogbones and a bespoke spacer... Rear motor/rwd.

That's good to know.  I’m not familiar with either of those models; my experience with Tamiya is rather limited.  It began with the Sand Scorcher, then I had a Monster Beetle for a short time bitd.  Next, came the Subaru Impreza only a couple years ago.  A big gap in time while I was away from the hobby.  Tamiya wasn’t on my radar until the Impreza and I’ve never owned an M or TL chassis.

Anyway, I'm going to keep those in mind for future builds.  Thanks!

[IXLR8]

So, I've just a couple more points to mention about chassis design before moving on…

To reduce tire scrub and optimize traction and handling, I wanted to provide some camber rise, eliminate bump-steer both front and rear and get the Ackermann steering geometry as near as possible to perfect.  Critical to bump-steer up front and Ackermann; the steering links are placed parallel to the lower arms and the steering rack assembly needed to be positioned correctly fore and aft to achieve correct Ackermann.   For this car, the image below shows the best location for the steering rack.  Moving the rack even a millimeter from this location will make a huge change at full steering throw so it was definitely worth spending some trial-and-error design time to position the assembly in the right spot.

Okay, I could continue writing about chassis design but I reckon it’s putting everyone to sleep so I’ll move on.

Anyway, while I was working on this project, a fellow TC member mentioned that Tamico has Tamiya 934 bodies in stock so I went ahead and purchased the body, light receptacles, spoiler and mirrors.

I really like the Vaillant-Kremer livery that was selected for Tamiya’s 45th anniversary car so I’ve bought the corresponding decal set from MCI.  Here’s a photo I found on RCDriver.com

So, it looks like I’m building two cars. 

I’ve ordered two sets of printed parts and have enough G10 and aluminum on hand to make two cars - the 251mm wheelbase RSR and a 232mm 934.  I just need the shocks, transmission and Traxxas parts to complete the second car.

For the RSR body, I’m thinking about trying to reproduce this incredible looking Singer I found on Youtube.

 

The color on this car appears fairly close to Tamiya’s Corsa Gray (PS-32).  I really like that color!

 

[GermanTA03Guy]

12 hours ago, IXLR8 said:

So, it looks like I’m building two cars. 

Hahaha i know that place...

 

By the way, there is no "correct Ackermann" - are you going for 0 ackermann effect ?  It can means of setup, so best might be if you make it adjustable to try different Ackermann setting and see which works best for you. Especially in your rwd rear motor construction i could imagine 0 Ackermann will create unwanted corner entry understeer, in the end you'll have to try. 

In my ta03s i have different lengths of the carbon steering bar that connects both steering arms to try various Ackermann setting... but up to now i havent tried them as im building new cars all the time ... 

[Nikko85]

On 4/9/2023 at 8:58 AM, GermanTA03Guy said:

Great stuff !!! Only shame is that the rwd rc cars always only have rear brakes.... theoretically, a 4wd Belt with a one way inserted the other way round could solve this. But i think youre too far for that and its 😎 like it is 

I have also seen an MF01x with one way diff in the front turned into a Porsche. 

Rear wheel drive rear motor but with front braking.

[GermanTA03Guy]

13 hours ago, IXLR8 said:

The color on this car appears fairly close to Tamiya’s Corsa Gray (PS-32).  I really like that color!

That will be great i think.

[IXLR8]

11 hours ago, GermanTA03Guy said:

Hahaha i know that place...

 

By the way, there is no "correct Ackermann" - are you going for 0 ackermann effect ?  It can means of setup, so best might be if you make it adjustable to try different Ackermann setting and see which works best for you. Especially in your rwd rear motor construction i could imagine 0 Ackermann will create unwanted corner entry understeer, in the end you'll have to try. 

In my ta03s i have different lengths of the carbon steering bar that connects both steering arms to try various Ackermann setting... but up to now i havent tried them as im building new cars all the time ... 

Ah yes, I know exactly what you mean.  My goal with this project was to minimize tire scrub on the inside wheel in a turn.  There are factors such as slip angle to consider but I’m just going for an initial baseline setup.  If I had simply placed the steering rack without first checking alignment at full lock, it could have been very bad.   I’ve managed to come close but it’s definitely not perfect – it should be tuned at the track.

One could very easily slot the bell-crank mounting holes as a way to adjust Ackermann.  RC steering blocks often include two or more steering link mounting holes that can be used for adjustment but the SC10 blocks I’m using include only a single hole and I don't want weaken them by drilling a second hole.

[IXLR8]

5 hours ago, GermanTA03Guy said:

That will be great i think.

Thanks.  I really need to purchase a couple tins and, using some lexan scraps, begin experimenting with different backing colors to achieve a final color a bit closer to the Singer in the image.  I normally back my colors with white but I'm thinking this will need gray instead.

Also, I need to locate a set of Fuchs wheels.  Is Tamiya the only source or do others who make them in 26mm and 32mm widths?

[IXLR8]

Okay, found some.

Yikes!   They are pricey, aren't they.

Must be silver plated gold.  

 

I reckon I'll keep looking.   

 

[GermanTA03Guy]

12 hours ago, IXLR8 said:

  My goal with this project was to minimize tire scrub on the inside wheel in a turn. 

Ah perfect, now i get it. I thought you went for perfectly parallel steering. But that does Sound correct ackermann indeed... also i wouldnt drill another hole in an existing rc10 part. You can dial it in with some toe out in case ... even if its not the same.

[ThunderDragonCy]

On the rear wheels, could you redesign the rear suspension with 16mm wider track and just use 24mm width wheels all round?

[GermanTA03Guy]

@ThunderDragonCy that would be a sacrilege and not scale at all honestly,  i cant imagine my 993 gt2 or any 911 for that matter without fat rear tires....and i think you can make the tamiya Fuchs wheels absolutely gorgeous with the right paint in the right places.

[GermanTA03Guy]

5 hours ago, IXLR8 said:

Okay, found some.

Yikes!   They are pricey, aren't they.

Must be silver plated gold.  

 

I reckon I'll keep looking.   

 

Yes and who knows how well they fit. With the tamiya wheels you definezely wont go wrong. Just paint them nicely, it makes a badword of a difference.

[IXLR8]

6 hours ago, GermanTA03Guy said:

Yes and who knows how well they fit. With the tamiya wheels you definezely wont go wrong. Just paint them nicely, it makes a badword of a difference.

I agree completely.  I also agree the Porsche really should have a staggered wheel and tire package.  Apparently Tamiya also agrees. I drive a Mustang GT with 255 fronts and 275 rears so, yeah, staggered tire widths are a must for me.

Anyway, I have these:

... so I can replace the 5-spoke inserts with nicely painted and detailed Fuchs caps.

Oh WOW, your 993 looks absolutely amazing!  By chance, do you have a build thread for this car?

[IXLR8]

6 hours ago, ThunderDragonCy said:

On the rear wheels, could you redesign the rear suspension with 16mm wider track and just use 24mm width wheels all round?

Yes, that is an option.  If I recall correctly, Tamiya has done this on their 30th Anniversary 934.

[GermanTA03Guy]

1 hour ago, IXLR8 said:

Oh WOW, your 993 looks absolutely amazing!  By chance, do you have a build thread for this car?

Thank you ! Yes there is one, final pics are on Page 4 of 5. My blueprint was kuhfarben's "senna's track tool" .

https://www.tamiyaclub.com/forum/index.php?/topic/100148-ta03-madness-continues-porsche-edition/#comment-888475