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[alvinlwh 7386]

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[djmcnz 755]

You're correct, Tamiya tend to be quite conservative.

8.23 is close enough to 8.1 that you don't need to worry. However, a 15 or 16T will be (marginally) more efficient. I'd not bother with the 15T but I would try the 16T to see if you preferred that, if not I'd have no concern going back down to the 14.

 

[alvinlwh 7386]

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[OoALEJOoO 3334]

I believe Tamiya recommends the gear ratio of their motors assuming they will be used with a specific tire size, dictated by the type of discipline they are intended to. This prevents users from having to do the math for different tire sizes.

For example, the Super Stock TZ for touring cars and the Super Stock BZ for buggies. I have these two on hand. They have the same exact specs and aside from their sticker look identical (and the BZ comes with a dust sponge). However, the manual recommends different gear ratios for each and I suspect it is because they are intended for cars that use different tire sizes:

If you do the math, the TZ with a gear ratio range of 6.5 to 8 (using 64mm touring tires) gives very similar final ratio of the BZ with a ratio range of 9 to 11 (using 88mm tires). In other words: 64mm/88mm=0.727 and you can see the TZ recommended range is very close to 0.727 that of the BZ (9*0.727=6.54 to 11*0.727=8.00).

In your case the Thunder Dragon utilizes 88mm tires, thus the recommended gear ratio would actually be 9 to 11.

Not sure what do you mean by uncontrollable at 6.77 (17T), but since this would be quite a long (tall) gear ratio,  I guess it had a significantly large top-speed. It would also mean a hotter motor.

[alvinlwh 7386]

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[alvinlwh 7386]

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[OoALEJOoO 3334]

1 hour ago, alvinlwh said:

Oh....that is interesting as none of the pinion options is 9 to 11, assuming the TD manual gives the correct final ratio? Or am I making a mistake again here somewhere?

Uncontrollable as in it will not do full speed turns without flipping over (some will say it is my poor driving, but since I am only a basher, I like full speed turns). There are some suggestions at using wider hex but there is no more room on the axle (without modifying the wheel) beyond 5mm hex.

This sounds like a by-product of the car going too fast because of the tall 6.77 ratio.

True, the vintage buggies seem to not have shorter gear ratio options. This seems to be the case in the Hotshot and Thundershot (Thunder Dragon). You best bet might be to go with 13T (8.86) and ideally a steel pinion.

56 minutes ago, alvinlwh said:

Do you happen to have a picture of the back of the box for the BZ? It may already list the recommended gears for my chassis. The reason I bought the TZ over the BZ is that the TZ is slightly cheaper with the same exact performance and many say the dust cover is useless anyway.

Unfortunately I no longer have the box which indeed had some gear ratios specific to chassis on the back. The manual doesn't have that info and google comes out dry 

[hIghQ 149]

BTW, shorter gear (=FDR number going higher), is harmless. Your car will simply accelerate quicker and have lower top speed (that's usually what bashers try to avoid at al cost). The opposite, gearing longer, can be "dangerous" as you can end up cooking (=overheating) your motor (not likely though, given the small gearing range most Tamiya cars offer, and the low power motors you seem to run).

Traction rolling can either be corrected with changes to the car setup (if is adjustable enough - most Tamiyas are not), tires, or indeed by driving style. Even in F1 cars have to brake for most corners.

[alvinlwh 7386]

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[Juggular 5089]

On 10/29/2021 at 5:01 AM, alvinlwh said:

Tamiya's gearing are generally quite safe for whatever you choose

That's mostly true. 

I'd say the instructions on TZ and BZ are interesting... because they are practically the same motors.  Same RPM, almost the same torque. Can they make every motor run at exactly 26,500 RPM?  One has 49mN.m the other has 500gf.cm? They are practically the same!  In this case, I would ignore the FDR on the motor. It's a very very flexible guideline.  The FDR on the chassis is far more important, because tire sizes, weight, 4x4 or 2WD are all included in the calculation.  

If you try FDR 4 on a buggy the motor will smoke.  Generally speaking, for buggies, down to 6 is okay if it's only run on a flat surface.  But because it's fast, it could spin out.  That has more to do with initial RPM than the gear ratio.   

Crawlers go down to FDR of 25, 35 or 45.  You could install a 3.5t motor on a 3S LiPo (like 8000KV x 11.1= 88,800 RPM).  Reduce that by 25 FDR, you still get 3500 RPM at the wheels and run donuts around all day long.  In comparison, the silver can's 14,000 RPM at 8 FDR gives you only 1750 at the wheels.  

You can go as low as you want.  If you have FDR of 100? As far as the motor is concerned, it's just a bench testing, without much load at all.  It's the lower FDR you should be careful of because lower FDR burdens with more load. 

FDR of 8 for a 4x4 buggy should be fine.  Say you installed big tires, so the circumference increased twice.  Without switching any gears, you've lowered the FDR down to 4.  We had TC members who did that and had the motors burn out.   

My rule of thumb is 6-7 and 8-9.  6-7 for touring cars like M-chassis.  8-9 for 4x4 buggies.  2WD buggies can be in between like 7-8.  Of course 4x4 can have FDR of 6 with a hot motor like TZ, but it can spin out (as you tested out).  Or, you can have FDR 10 for M-chassis, but you won't win any races with that gear ratio.  

No matter what the box of the motor says, I would not make the ClodBuster run at FDR 6.5.  That's a heavy chassis with huge tires, you need much lower gearing (FDR 29.9).  F104 chassis have the FDR of about 3.5. Because it's a very light chassis with small tires.  FDR 30 or 3.5, both chassis could use Super Stock motors.  So, I would just go with the chassis' FDR and my own experience of running it (which you did), than paying attention to the instruction.  

 

[alvinlwh 7386]

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[Juggular 5089]

If possible, perhaps you could adjust the acceleration?  Some radios have that function. 

I think if you are lifting inner wheel already, hard oil could make it roll over faster.  Softer suspension makes the turns wider and thus less likely to roll. But obviously, you don't want it too soft to have a wobbly steering.  Harder suspension makes the turns more precise and more likely to roll over.  Trying things this way and that way leads to more understanding, and that is a major part of the fun. 

On that note, you could try the LSD, (not the psychedelic stuff, but 'Limited Slip Differential') by using sticky differential grease.  If the inside wheel is lifting, the outside wheel has already lost power. It's a 2WD at that moment. (We've all seen a 4x4 buggy ballooning one front tire that's up in the air, while the other one does nothing.)

With a LSD, it would be 3WD when the inside wheel lifts up.  Having some power on that one steering wheel on the ground could help the buggy go doggedly go where it couldn't before.  For a buggy Anti-Wear grease is too weak.  Diff clay is too hard for the front diff.  '3Racing Ultra high viscosity Differential Oil' is still not as sticky as I want, but it's a lot sticker than AW grease, so I use it for my buggies (but most of my buggies are 2WDs).  

I don't know if it would make it easier to roll over on high-traction surface or not, because of the one steering wheel on the ground forcing the turn, instead of meekly being pushed.  On the other hand, it does lose some torque. LSDs won't let the tire on the ground have 100% of the torque, more like 40% with 3Racing stuff. (Only 5% with AW, I feel.)  So it might not oversteer. And spools understeer, but a LSD isn't a spool... (you see, I'm still figuring things out myself...if you figure it out, please do let us know.)   But generally speaking, 1:1 Subarus with LSDs can go more places than bigger 4x4s.  It's something to think about. 

 

[alvinlwh 7386]

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[Wooders28 4957]

On 10/29/2021 at 11:04 AM, alvinlwh said:

Now don't get me started on trying to find 0.8M 10T pinions with 3.175mm bore... 😅

I don't know how you feel about not running true 08 mod, but 32dp are close enough to tolerance to run (07938 mod). I run these in pretty much all mine (except where they came with a steel pinion, or got an 08 cheap enough..), the only issue I've had, is when sand got in and munched everything. 

https://www.modelsport.co.uk/product/schumacher-pinion-hard-alloy-32dp-10t-1340792

[alvinlwh 7386]

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[Wooders28 4957]

1 hour ago, alvinlwh said:

How I feel... Well I am a RC newbie, so not sure what to feel about mixing and matching parts, not just pinions

Some people like to keep pinions absolutely spot on, (08mod - 32dp are the only mod-dp that work btw), I'm not overly bothered, as I tend to overpower them and push boundaries anyway, so breaking parts is expected (although, I've not broken a gearbox as yet, even running brushless and 3s -5s, it's usually keeping the nose down or grip ,that's an issue) 

[Rich54129 1]

On 10/29/2021 at 12:11 PM, alvinlwh said:

Do you happen to have a picture of the back of the box for the BZ? It may already list the recommended gears for my chassis. The reason I bought the TZ over the BZ is that the TZ is slightly cheaper with the same exact performance and many say the dust cover is useless anyway.

Here you go..  I bought a BZ motor last week and still have it in the car, box pic attached.  There's nothing specific on the box re: chassis types, just the same gear ratio range as in the instructions..

I've bought a re-re Terra Scorcher which I'm currently building.  I've not looked into ratios, I'm just fitting the BZ with a 13T steel pinion that I've seen recommended, as there was talk of motors getting too hot with a bigger pinion.

Necessary I think also as I'm putting bigger diameter tyres on than stock which will lengthen the gearing; the BZ spins a lot faster than a silver can so think the car will still be faster overall?..  If not I 'll upgrade it some more!

[alvinlwh 7386]

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[alvinlwh 7386]

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[Wooders28 4957]

31 minutes ago, alvinlwh said:

I had just recently cracked a drive cup and twisted a dog bone 90 degrees although that is mainly due to poor maintenance and "user error". 😢

Could be worse, could just be sat on a shelf.....🙄😁

[SuperChamp82 745]

@Juggulars comments re chassis vs motor FDR are spot on  

A much more simplistic approach is also to hold your finger on the motor after running - and if it’s too hot / you can’t comfortable stay there for 2s - the pinion is too big / overloading.

Conversely, if only the battery is getting hot, the pinion is normally too small.

And if the ESC gets too hot - stop before it pops … and either change it or your motor 😂

Playing with pinion size, motor and tyres will then (eventually) get you to a sweet spot for your driving style and different tracks / conditions 👍

[alvinlwh 7386]

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[hIghQ 149]

15 hours ago, SuperChamp82 said:

A much more simplistic approach is also to hold your finger on the motor after running - and if it’s too hot / you can’t comfortable stay there for 2s - the pinion is too big / overloading.

Not only more simplistic, but also very inaccurate, I'm afraid, as different people can have very different sensitivities to temperature. What's too hot for person A to endure, is no problem for person B. So take these "touch the motor for x seconds" method with a massive grain of salt. Get a cheap IR-thermometer instead, if you are pushing your motors.

[Willy iine 18831]

Actually that thumb touch approach works fine for brushed motors.  I used it during my racing days and as a habit I even do it today to verify gear ratio and my driving style for that particular driving condition.  I mean using a thermometer never hurts and if you have one, go for it.  

Some thermometers aren't all that accurate all the time as some of the ones I've seen needed to be soaked to the measuring environment before it can properly calibrate itself.

[silvertriple 4116]

3 hours ago, hIghQ said:

Not only more simplistic, but also very inaccurate, I'm afraid, as different people can have very different sensitivities to temperature. What's too hot for person A to endure, is no problem for person B. So take these "touch the motor for x seconds" method with a massive grain of salt. Get a cheap IR-thermometer instead, if you are pushing your motors.

infrared thermometer. If the motor is above 60°C after 5 minutes reduce pinion 1 teeth. If way below, you still have margin for additional tooth