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IXLR8

Porsche 911 with bespoke chassis

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6 hours ago, IXLR8 said:

Okay, hmmm, I know nothing about that chassis so I'll need to price it out and see if it fits the budget.

Meanwhile, I'm taking a hard second look at the scratch build approach using my 2wd chassis as a template.

I'll definitely want to keep the trailing arms and use the same transmission but simply spinning the motor and trans around 180 degrees (making it mid-motor) causes interference with the spur gear and the upper radius rod and shock.  There's simply no way that will work without major suspension design changes so I'm thinking about keeping rear motor but moving the servo to the side so I can slide the battery forward for more front weight.

Also, I found some timing belt pulleys on ebay for cheap - less than $3 each - but they are MXL 2mm.  If I go forward with this , at some point I'll need to decide between MXL (trapezoidal, 2mm pitch) or HTD (curvilinear, 3mm pitch)?  I'm used to designing with gears not belts so this is new to me.  :rolleyes:

 

I think keeping it rear motor and scale correct is the cool option anyway. The xv01 works by having an extended idler shaft that runs through to the outside of the case to mount a pulley, but that requires the idler to be attached to the shaft somehow and bearings in the case. If your transmission doesn't work like that I guess a longer layshaft drive directly from the spur gear would be best. 

I don't know much about belts either, but rc car belt tend to be 2mm wide and square tooth from what I can see. 

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Yes, it's common to drive the belt from the idler gear shaft but the transmission I'm using has a static idler shaft (bearings are in the gear) so that won't work.

Instead, I'd need to drive the belt from the input (spur gear) shaft.  Not ideal but it does raise the belt and provide more clearance for a battery.

Friction loss is a big concern so it's best to use a narrow belt.  Schumacher, Yokomo and others use narrow belts but I'm finding 3mm as the minimum standard belt width and it's the MXL standard (trapezoidal).  According to my very limited research so far, trapezoidal is best suited for registration but curvilinear (i.e. HTD) is best for high speed and high torque applications.  The narrowest HTD belts I'm finding are 6mm wide.  It's possible that Schumacher, Yokomo, etc., are having their narrow curvilinear belts made to spec so they can handle torque while minimizing friction loss.  Call me crazy but I believe I could very carefully slice a wider belt into thinner sections.  Anyway, I'd give it a try.

Further to the friction loss issue.  While belt idler pulleys can provide a means to tension the belt and increase tooth engagement count, they also will increase friction so I'd try to avoid using them - at least initially.  Tension can be adjusted by slotting the transmission mounting screw holes.  If skipping becomes a problem, idlers could be added later to increase tooth engagement.

Hopefully, I've gotten it right but someone please correct me if anything here is incorrect.

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I think I just made a HUGE mistake.  I bought this well used "TA02" for a price that was within my budget thinking I could simply replace the chassis and convert it to a TA02SW for the GT2.

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After making the purchase however, I've discovered that the front arms (bones) and steering hubs are not the same as SW.  Not sure if the front suspension parts are different to increase the SW's front track width or for some other reason.  Please post a comment if you know why these don't match the SW's parts.

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Anyway, maybe that's not the full extent of the damage - maybe the axles are different as well??  I'm kicking myself now for wasting money on this thing.

I know nothing about the TA02 and its variants so could someone please help me determine which parts are needed to make this chassis fit a Porsche GT2 body?

thanks.

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To get that to fit a Porsche GT2 TA02SW body you would need the TA02 tub to rebuild your parts on to - keep the TA01 rear arms but fit them in reverse to shorten the wheelbase and get the standard blue / black TA02 or TA03 front uprights. On the TA02SW the extra width is provided by the wheel offset on the two piece mesh or five spoke wheels.

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3 minutes ago, Superluminal said:

To get that to fit a Porsche GT2 TA02SW body you would need the TA02 tub to rebuild your parts on to - keep the TA01 rear arms but fit them in reverse to shorten the wheelbase and get the standard blue / black TA02 or TA03 front uprights. On the TA02SW the extra width is provided by the wheel offset on the two piece mesh or five spoke wheels.

You will also need the shorter TA02 prop shaft, and if you want to fit the TA02/3 knuckles you need the arms, 42mm driveshafts and different axles. There isn't really any need to do the front suspension though. The TA01 stuff you have there is the right width and same wheelbase. 

You have been sold a pup by that seller though. That is absolutely not a TA02

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Thanks everyone.  Having read through your comments and information contained in the links, the chassis is indeed a TA01.

My initial thought is that I've been deceived however the seller listed the chassis: "For parts TAMIYA TA-01 / TA-02 TA01 / TA02 chassis with motor".  I can't return the chassis claiming that it has been misrepresented so I'm stuck with it.  Unaware of the differences, I saw "TA02" and hit the BIN.

Anyway, this chassis will never find its way under my GT2 - the cost to convert to a proper SW is too high - but I might have another use for it.

I have Tamiya F-150 and Toyota Prerunner re-pop bodies that currently ride on a shortened Vaterra V100 chassis.  The V100 runs well but it's not Tamiya.  According to the very comprehensive model comparison posted above, the F-150 chassis uses TA01 suspension parts but they are fitted to the shorter TA02 tub.  Maybe I could replace the chassis tub and prop shaft or simply reverse the rear arms to achieve the correct wheelbase for those trucks.  I'll have a close look when the chassis arrives in a few days.

Thanks again everyone.

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Well, the TA01 chassis arrived today and the rear arms are reversed but the wheelbase is still about 8 - 10mm too long for the F-150 and Prerunner bodies. 

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So, I could replace the chassis tub and prop shaft to make it shorter but I may have a better idea.

The TA01 chassis is in very good condition considering the age and it still has the original MSC with resistor and a couple vintage Sanwa servos.  Everything appears to be intact, assembled per the manual, and in good shape so I think I'll clean it up and fit it with a BMW M3 body to keep it somewhat original.  TBG makes a re-pop body and MCI offers the complete reproduction decal set.   The correct wheels and tires should be easy to find -- in fact, I might already have those wheels.

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I think it will look nice setting on the shelf next to the Porsches.  :)

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I've spent some time lately developing the rear motor, belt drive chassis for the new GT2 body and here's where we are at the moment.

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The arms, C-hubs and steering knuckles have been roughed-out (the C-hubs are very rough at this stage) and only the front bulkhead remains to be designed.  That 3-gear transmission fits nicely between the arms and within the steering linkage...

 

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... but it doesn't leave much room for a bulkhead to tie everything together.

 

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Designing a single part that attaches the inner arm and camber link pivots and shock tower to the chassis plate while providing space for the transmission to slide fore and aft for belt tensioning is proving to be a challenge.  I'll get there eventually - I just need a little inspiration.  :unsure:

Meanwhile, I really want to drive the new GT2 with all four wheels pulling (and braking) so I'll show what I've come up with in the next post.

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Picking up from my previous post, I have the belt drive chassis design well underway but it's taking some time to finish and I'm impatient to drive the GT2 so I've gone ahead and purchased a clone TT-01 from an ebay seller.

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I've fabricated shorter chassis plates (6061 bottom, G10 top) and shortened the prop shaft to achieve the 236mm wheelbase needed for the GT2 body. 

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Out of the box, the chassis included some nicely anodized aluminum drive cups, axles and dog bones but the ball ends were undersize and fit so loose in the drive cups that I was certain they would fall out on the first turn.  To spare myself the frustration, I've gone ahead and swapped them with parts from a TT-02 shelf car.

I've driven the car a few times and overall handling performance is underwhelming.  I'm running Tamiya slicks and the car seems well balanced through the turns but in the straights, it won't hold a line - wandering from side to side and requiring constant input to keep it straight.  I believe this is the result of loose fitting suspension parts - especially at the a-arm ball joints.  Like the dog bones, the pivot balls are too small to properly fit the sockets in the arms.  If you've ever driven an older, high mileage 1:1 vehicle with worn suspension and steering components, you'll know what this is like.  It's unpredictable and requires constant attention at the wheel to avoid landing in the ditch.

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On the second outing, it lost drive because the plastic collar on the spur gear slipped forward allowing the drive pin to be ejected.  What a horrible design - it appears to be meant for this to happen.  Why is a separate collar needed anyway?  They can mold wheel hexes with recesses to capture the drive pins so why can't they do that with the spur gear??  :wacko:

Anyway, it is what it is.  Maybe I could lathe cut some larger pivot balls but it's probably not worth the effort.  When the belt drive chassis is finished, I'll reassemble this chassis with the original longer carbon fiber chassis plates so it can prop-up the RSR body on the shelf.

I'll post photos of the finished GT2 body in the next installment. 

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So, the finished body isn't different from what you've probably already seen - just standard StarCard/Taisan livery.  All screw holes in the wing were filled and the wing assembly and mirrors have been lacquer clear-coated and polished.  Also, the photos don't show it well but I've used metallic rather than solid black.  It sparkles a bit in the sun light.

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I've used some scrap lexan to plug the front body mounting holes.

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Perhaps the only significant difference from Tamiya's kit body is the lighting inserts from Tamico.  

https://tamico.de/Tamico-Lichteinsaetze-vornehinten-fuer-Tamiya-Porsche-911-GT2

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Congratulations on some very good work on the body.

Looking forward to your next iteration of a personal chassis design. 4WD on a Porsche used to make my teeth grind 😅 but over time I have learned to admit that brakes on the front wheels are important!

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On 7/21/2023 at 1:15 PM, Pylon80 said:

Congratulations on some very good work on the body.

Looking forward to your next iteration of a personal chassis design. 4WD on a Porsche used to make my teeth grind 😅 but over time I have learned to admit that brakes on the front wheels are important!

Thanks!

Yeah, I have a newly found appreaciation for four-wheel braking.  

The Porsche 934 is probably the first two wheel drive on-road car I've driven since racing my 10L pan car nearly 30 years ago.  Back then, we raced foam tires on carpet and tarmac but I don't recall the limitations of two-wheel braking being an issue or even being discussed.  With my two-wheel Porsche, leaning on the brakes a little too hard will cause the car to immediately swap ends.  Maybe sticky tires would improve things but I'm guessing braking with that car will still be a problem.

I'm currently restoring a TA01 BMW M3 but I'll get back to the belt-drive Porsche chassis when that project is finished.

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