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OoALEJOoO

RWD TT-01E or TT02? One-Way Unit Question

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Merry Christmas to all :) !

On the L&L body thread, @TurnipJF commented that a TT02 can be easily converted from 4WD into RWD by simply removing the front drive train. Always looking to further tweak something :), this has crossed my mind several times to do it on a TT01, but the though of the axial force generated by the bevel (conical) gears has kept me undecided.

Fig16-6.jpg

When the TT01(2) is 4WD, the axial force created by the front bevel gear will cancel out with the one created in the rear, the propeller shaft would be "axially balanced". If either the front or rear drivetrain is removed, then the propeller shaft will have a net axial force, which would have to shoulder somewhere and create friction. EDIT: As rightly pointed out by @DeadMeat666, since the propeller shaft has axial play from the cups, it actually does not transmit axial force.

  • In the case of a RWD TT01, I think this shouldering would happen between the spur gear stopper (part GB2 on pic below) and the chassis. High-speed friction under load with plastic-against-plastic seems like a no-no. I have melted this GB2 part in the past and this was with the stock 4WD :o. EDIT: As rightly pointed out by @TurnipJF, the shoulder actually happens on bearing RB1 because GB5 contacts it via it's prongs.
  • Looking at a RWD TT02 however, it seems that this axial load would be taken by a 1150 ball bearing (BB2 on pic below), which indeed means it should be more manageable (a regular radial BB can take a bit of axial load).

RWD.jpg

Isn't this axial load the reason why some cars have thrust bearings/bushings behind bevel gears (e.g. Terra Scorcher)?

Having said the above, there should also be an axial force acting on the bevel gear part of the differential case. Since this gear has quite a large diameter, I suspect the axial force largely becomes a bending moment and thus the force ends up mostly acting radially, therefore taken by the radial ball bearings right where the differential case is mounted.

I'm curious if anybody has some mileage with a TT01 or TT02 running in RWD that can share some insights and experience. Thanks in advance! :)

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Try just taking the front drive cups and dog ones out an see how it feels!

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1 hour ago, OoALEJOoO said:

When the TT01(2) is 4WD, the axial force created by the front bevel gear will cancel out with the one created in the rear, the propeller shaft would be "axially balanced".

Wouldn't that only be true if the driveshaft was in full contact with both drive-cups at all times? As far as I'm aware, driveshafts in the TT01, TT02, or any shaft-driven RC should have some (axial) play in them, to account for chassis flex, which is why there are little foam pieces, or springs, or even just a small space between the driveshaft and each of the front and rear drive cups.

So in practice, there is similar axial force on the driveshaft in 2WD than there naturally is in 4WD 'mode'.

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Very interesting Topic.

Im curious about this as well - Would like to build a porsche on the tt02 chassis it comes with and have it act sort of like a real porsche would (or at least how i think it would if you turned off the Traction Control). 

I asked this to a LHS employee and they responded . . ."Why not just get an M08?"

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8 minutes ago, Greanie said:

Very interesting Topic.

Im curious about this as well - Would like to build a porsche on the tt02 chassis it comes with and have it act sort of like a real porsche would (or at least how i think it would if you turned off the Traction Control). 

I asked this to a LHS employee and they responded . . ."Why not just get an M08?"

Prepare to be disappointed. The TT02 chassis is not designed to be run in RWD only, so you'll mostly be doing donuts*. In fact it's quite difficult to drive any 1/10 RC road car in RWD, but those that are designed to do so have more weight on the driven wheels. Even the M08 is quite a handful unless you're a. really good, and b. on a high-traction surface like carpet. The instant torque that electric motors have combined with the loss of braking in the front wheels conspire to make RWD road cars very frustrating to keep on track.**

* Source: personal experience from trying it myself.
** I have an M02, and M06, and an M08, which are all RWD platforms.

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12 minutes ago, DeadMeat666 said:

 

 I have an M02, and M06, and an M08, which are all RWD platforms.

No M04!?

Now that is a tricky chassis to drive with any pace

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11 minutes ago, svenb said:

No M04!?

Now that is a tricky chassis to drive with any pace

Actually I do, I just forgot that I did lol.

I bought one used from eBay a couple months ago, but I haven't gotten around to using it yet.

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5 hours ago, OoALEJOoO said:

When the TT01(2) is 4WD, the axial force created by the front bevel gear will cancel out with the one created in the rear, the propeller shaft would be "axially balanced".

TT0x has a 3-piece driveshaft, with slight axial play - so no force is transmitted between front and rear. Even if it was rigid, it'd probably never cancel out the axial force, because one end typically transmits more power due to weight shift.

So you can remove driveshaft without worries :) However, it'll only work on high grip surface - RWD needs more rear-biased weight distribution.

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Both TT chassis have the axial load born by the bearings, RB1 on the TT-01, BB2 on the TT-02.

On the TT-01, the "prongs" on the spur gear protrude through the gear stopper and engage with the bearing. 

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12 hours ago, DeadMeat666 said:

Wouldn't that only be true if the driveshaft was in full contact with both drive-cups at all times? As far as I'm aware, driveshafts in the TT01, TT02, or any shaft-driven RC should have some (axial) play in them, to account for chassis flex, which is why there are little foam pieces, or springs, or even just a small space between the driveshaft and each of the front and rear drive cups.

So in practice, there is similar axial force on the driveshaft in 2WD than there naturally is in 4WD 'mode'.

This makes perfect sense. The propeller shaft indeed has significant axial play. Moreover, after a closer inspection of the cars, the cups at both ends have almost zero axial play and therefore the shouldering must happen inside the gearboxes.

4 hours ago, TurnipJF said:

On the TT-01, the "prongs" on the spur gear protrude through the gear stopper and engage with the bearing. 

After further inspection, indeed the prongs do protrude towards the bearing, which would take the axial force.

Based on the above, it seems then that there are no reliability-related concerns in converting a TT-01 or TT-02 into a RWD. It would handle terribly but should not melt its gearbox. Time to give it a try :)

I'll start with my old & beaten TT-01E by removing the propeller shaft. I'll keep the front gearbox but with a fully locked differential as an attempt to reduce oversteer.

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Just now I did the RWD conversion on my trusty TT01. The propeller shaft was removed along with the front propeller cup, with the opening to the front gearbox plugged with duct-tape. All the front drive train remains, but with a fully locked front diff to reduce oversteering tendencies. Also added some toe-in on the front.

Since now all the power will be provided to the rear wheels, I decided to swap its Super Stock TZ motor with a regular silver can. I kept the 6.28 FDR, which is quite long, to tame the rear. Will be using a Porsche GT2 shell, with wide tread on the back and also 32mm wide rear tires. This fat rear end should also help keeping it a bit more controllable (hopefully :)).

3.JPG

Right before going out to test, nasty clouds strike with quite a lot of rain. Testing will have to wait!

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I ran my Terra Scorcher for a while without the central propshaft. When I was just bashing around the garden and drive it was too predictable and easy to drive as it were. I fancied something a little more of a challenge, and doing big oversteer powerslides were difficult but fun to achieve and hold .

When I started trying out the postal racing, that unpredictability became frustrating, so the propshaft when back in quite quickly...

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Reporting back after running two full battery packs with the RWD TT01E.

To recap, the state of the car before the conversion was:

  • 4WD
  • Front differential with just a bit of AW grease, rear differential completely loose
  • Super Stock TZ motor
  • 24T pinion + 58T spur for a 6.28 FDR
  • Front toe-in neutral

After the conversion (all things done to try taming the "unbalanced" RWD):

  • RWD
  • Front differential locked, rear differential remained completely loose
  • Stock silver can motor
  • 24T pinion + 58T spur for a 6.28 FDR
  • Added a bit of front toe-in

I must say, what a lovely drive! :) The test was done on a low grip parking lot.

The car had good acceleration and top speed, a bit lower than when running the Super Stock, but not much slower. It felt very balanced and well behaved, perhaps only a tad of oversteer when braking. In fact, it had much less power oversteering than when it was 4WD! I think this mostly has to be the locked front diff, but still it was a nice surprise.

I haven't dismantled the rear gearbox to check for any damage, but per the above posts, logic tells there should not be any difference in axial loading. The drive train remained smooth and free after the two battery packs.

Highly recommended mod!

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Glad it was a success! I think your motor choice played a significant role there. It is easy to over-power a RWD, making them very hard to handle. Moderate power often translates to smoother driving and ultimately better lap counts. Case in point: I can usually out-lap my mate with his 8.5t F104, driving my humble 21.5t F103, simply because I spend a lot less time spinning out and hitting barriers! 

Are you planning any further developments? If so, please keep us posted!

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54 minutes ago, TurnipJF said:

Are you planning any further developments? If so, please keep us posted!

I'll enjoy the car as-is for a while. Once I really get the hang of it, the silver-can will get swapped back to the Super Stock TZ. In theory it could be just as controllable with the right level of skill :) I might change the 6.28 FDR to the longest 5.72 to tame it a bit.

Thanks a lot for you earlier insights in making this happen. It is breathing new life into my TT-01E !!

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Good work! Glad it went well. Motor power is a very good point. I was running my TA06 with a 17.5 brushless. I do have a rear drive car - my RR03-Ra - the hacked trf201 rear motor buggy chassis with touring car arms - and that's really fun to drive but it took a long time to get it good. The key was very evenly setup suspension front to rear. Your tt01 must very nicely set up. I have also tall gearing with a torque tuned motor the most fun with the RR03. I think I am running about 5.5 fdr and its surprisingly quick. 

Just a quick note on tt01 gearing - tamiya doesn't publish it but you can run up to 28t pinion on the 55t spur to get down to 5.11 fdr if you want to keep motor performance modest and power manageable. 

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Just wondering, a RWD TT will behave more like a MR than a RR right? 

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On 12/26/2021 at 7:19 AM, svenb said:

Or a one-way fitted the wrong way

I agree!  You don't want to take away the front wheels' ability to brake.   Maybe a drift gyro might be useful too.

 

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11 hours ago, Grumpy pants said:

Do you think the results would be the same with a TT02 chassis? 

Yes, I would anticipate the TT02 to have very similar results. The spur arrangement of the TT02 is nearly identical to the TT01E, where piece GB3 transmits the axial load to the bearing (instead of the prongs + GB2 on the TT01). The TT02 is very similar in weight balancing to the TT01E and should control along the same lines.

Having said that, using ball bearings (RB1/BB2) is recommended. If using plastic bushings, then there will be axial rubbing between the plastic bushing and chassis which will lead to heat and possibly binding. The axial loading will be a bit higher than 4WD given all torque is now on the rear end.

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On 12/29/2021 at 5:37 PM, ThunderDragonCy said:

Just a quick note on tt01 gearing - tamiya doesn't publish it but you can run up to 28t pinion on the 55t spur to get down to 5.11 fdr if you want to keep motor performance modest and power manageable. 

Quite interesting! Does the same apply to the TT02? I see that for the 64T spur, the manual stops at 29T pinion but there are still two more positions for larger pinions (30T and 31T, are they available in 06 mod?).

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6 hours ago, OoALEJOoO said:

Quite interesting! Does the same apply to the TT02? I see that for the 64T spur, the manual stops at 29T pinion but there are still two more positions for larger pinions (30T and 31T, are they available in 06 mod?).

Yes, but you have to be careful of clearance. You can get 0.6mod bigger than 29t, but Tamiya don't make them. RW Racing in the UK does. The other thing with TT02 kit is you can ditch the 0.6mod completely and switch to 48dp or 64dp which are much more common in touring cars, and smaller pitch so you can get lower fdr gearing for smaller spur gear and larger pinion but still fit in the gear case. 

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