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bsr077

Help Gearing Tamiya Df03ra

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Hey all so I just picked up one of these, have installed the slipper clutch and heat sink bars, the kit came with a 75 and 78 spur and a 28 and 32 pinion

I have a 15t motor in there and it gets super hot even at 28/78 which is a FDR of 8.22

Any ideas?

Even my 20t motor gets hot at that FDR

Am I destined only to run the silver can?

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Shouldnt get that hot. How close is your pinion mesh?

Spot on, no binding in the transmission, checked the mesh and reset it with paper between gears etc, all good.

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I went through this same problem with my Durga and finally found the answer via the formulas below. This was the best way to target the optimal pinion for your gearing. It cannot however factor in the resistance of your motor (lower resistance = more heat), but it will let you know if your gearing is adding strain to the motor which will also produce more heat.

The formulas are mostly needed when using a brushed motor since heat and resistance is greatly reduced with a brushless motor, so your gearing can be more aggressive.

I used these formulas myself while I was still running brushed motors. I later switched to a Novak brushless and gearing became easy since they provided a gear ratio chart for their motors :lol:. You can always use this website if you want to create a bigger gear ratio chart for your DF03 - www.gearchart.com

P.S. If you have questions about the formulas, just let me know. I can figure out your gearing and post a chart for your car.

Solving the gearing problem:

What size spur gear should I run? What about the pinion gear? Well. When selecting the spur gear and pinion gear size, you need to understand that there is a ratio between the tire circumference (referred to as roll-out) and the final drive ratio. That ratio, in most cases, should be as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I am referring to the distance traveled by the tire in one revolution to the number of revolutions turned by the motor. In other words, if the motor turns X number or RPM's, the wheel will turn at Y RPM's, which is reduced by the final drive ratio. (A 32000 rpm motor with a final drive ratio 10.9893 will turn the tire at 2912rpm). For the sake of efficiency, the vehicle should be geared so that tire should travel approximately the same distance for every revolution of the motor, reduced by the final drive ratio. Heres how it works. Well use my RC10t3 as the example vehicle. The first thing to consider is the diameter of your tire. It is used to calculate the circumference of the tire. Multiply the diameter of the tire by pi. ( Ex: 3.25xpi=10.2101) Now, you need to consider the final drive ratio of your drive train. Begin by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear. This will give you your drive ratio. ( Ex: 87/19=4.5789). Now multiply your drive ratio with your transmission gear ratio ( Ex: 2.4x4.5789=10.9893 ). This is your final drive ratio.

Now the magic part. Subtract the final drive ratio from the roll-out of your tire . (Ex: 10.2101-10.9893= -0.77926) That is VERY close to a 0, but is geared a tad to the torque side of the motor ( anything below 0 is always geared towards more torque). Want more speed than torque? Redo your calculation adding another tooth on the pinion : ( Ex: 87/20= 4.35 ( drive ratio )x2.4 ( transmission gear ratio )= 10.44 ( final drive ratio ) Then subtract your final drive ratio ( 10.44 ) from your roll-out ( 10.2101 ) ( Ex: 10.2101-10.44= -0.2299 ) This is your optimum gear ratio, since it is closest to a 0 margin. Any ratio that is greater than 1 will run faster, but will overheat your motor, battery and esc, eventually damaging them.

How do we know this works? We can check out math by multiplying the roll-out of the tire, by the number of RPM's delivered to the tire, via the transmission. (Ex: Vehicle Final Drive Ratio is 10.44:1 and the roll-out of a 3.25" tire is 10.2101 " X 3065 rpm= 31294rpm) The motor's peak RPM is 32000, which means that we have less that 3% loss in efficiency from the motor, through the gear train.

Overgearing a vehicle will add to the speed of the vehicle, but it does so at a tremendous cost. The additional strain placed on the motor by the shorter gearing, will cause tremendous heat build up as the motor struggles to reach its peak RPM.

While this formula is not absolutely perfect, it does allow you to select a safe, and scientific starting point, to determine what is the best gearing combination for your particular vehicle.

This formula works best with 1/10 scale vehicles running stock to mid-modified motors. ( 27 turn to around 12 turn motors ).

Hotter motors 12 turn and lower will require you to reduce the ratio by as much as -1 or even lower to combat heat build-up.

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Thanks for that, with Rally blocks, by your theory their ratio is 8.79

I just ran a 15 turn motor at 9.53 which by your reckoning is geared to the torque side, -.74

Then motor came off at 65 degrees celcius, this is a brand new motor.

So I assume if I run it at 8.79 it'll run hotter? How hot is too hot?

The theory seems nice, but it doesnt seem to account for whether I run a 27 or 15 turn motor, by what you have written, I'd gear them all at 8.79?

*confused*

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For a starting point for a 15 turn motor I would say an FDR of 8.5-9.0 would be a good starting point, assuming the motor is in good condition. Part of the problem is the chassis design, there's no cooling air passing over the motor and not much you can do about it, so I would suggest you might have to gear even higher like 9.5-10:1 to try and keep the motor cool.

Reducing the timing advance on the motor will lower the top speed but give you more torque and use less current, so cutting down how much heat the motor creates. If you are planning on trying this make sure you mark where the timing is set before you do anything so you can put it back if it makes no difference.

The theory seems nice, but it doesn't seem to account for whether I run a 27 or 15 turn motor, by what you have written, I'd gear them all at 8.79?
Correct, it's garbage. It's been around for years and blinds most people with all the technical formulas into believing it means something.

It doesn't make any allowances for the motor at all, so you end up with the same gear ratio for a 55 turn crawler motor and a 12 turn race motor. It also doesn't consider what track you are running on, it gives the same gear ratio for wide open high speed running and a small stop/start track.

I just ran a 15 turn motor at 9.53 which by your reckoning is geared to the torque side, -.74
So according to the calculation above the motor is way undergeared ;)

The checking out the math to "prove" it's right doesn't actually prove anything.

Ex: Vehicle Final Drive Ratio is 10.44:1 and the roll-out of a 3.25" tire is 10.2101 " X 3065 rpm= 31294rpm
If the final drive ratio is 10.44/1 and the motor rpm is 32,000 then the wheel rpm is 32,000/10.44=3065 rpm. Now you take a number that works out to be near 1 (the tyre circumference minus the final drive ratio) and multiply the same formula by this and (surprise surprise) you end up with a figure near the motor rpm.

The only use that formula has is making sure you adjust gearing if you fit bigger or smaller tyres on the car, something that's important if you are running pan cars where the tyres are shrinking as they wear, although there are much simpler ways of working out the new ratio from the old one.

While this formula is not absolutely perfect, it does allow you to select a safe, and scientific starting point, to determine what is the best gearing combination for your particular vehicle.
So the formula just gives you a gear ratio to start from, then you adjust it to suit. :lol: In other words you can throw on any mid range gear ratio you like without wasting time going through the calculations and adjust it up and down to get it right. :P

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Thanks for that, with Rally blocks, by your theory their ratio is 8.79

I just ran a 15 turn motor at 9.53 which by your reckoning is geared to the torque side, -.74

Then motor came off at 65 degrees celcius, this is a brand new motor.

So I assume if I run it at 8.79 it'll run hotter? How hot is too hot?

The theory seems nice, but it doesnt seem to account for whether I run a 27 or 15 turn motor, by what you have written, I'd gear them all at 8.79?

*confused*

I agree. I didn't write the math (I got that part off of another forum), but its the closest thing I found that could ballpark which pinion might be best for the gearing of an rc car. The math doesn't really take the motor into account which is part of the problem; it just tries to regulate the gearing of your car and is kind of handy when you change spur gears etc.

I used it when I was running a 27T Trinity and a 19T Trinity at the track. It helped for sure and brought my temps down from 170F+ to 150F after a full run. The only basis the math provides to test the gearing is by the RPM of your motor. Trinity provided RPM stats, so at least I had that.

I never found target temps for brushed motors, but I did find temp ranges for brushless motors saying that they should never exceed 160F (71C). The other rule going around is the '5 second rule' - If you can't hold your finger on your motor for 5 seconds after it has been run, then it is too hot. I don't really agree with that method, but a few guys on the track were doing it.

The best thing a motor manufacturer can do is provide a chart of recommended gear ratios for their motors and the cars they are being used in. Novak is the first company I have found that does this, and it made it "really" easy to target the best pinion / spur combos for my car (using www.gearchart.com)... Did the Novak motor run cooler and my car perform better - you bet it did.

I'm really confused why other motor manufacturers don't do this? It would save a lot of time and effort..

Dan

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The problem with motor manufacturers supplying recommended gear ratios is that it is impossible to use one gear ratio for every track. If someone is told to run one particular gear ratio by the manufacturer then they will run that ratio whether it is appropriate or not. For example a touring car with a 19 turn motor is usually geared around 7 to 7.5/1, I run a 19 turn motor on my small local track with an overall ratio of 9.8/1. But the same motor in my pan car (same tyre diameter) is geared correctly with a ratio of 7.4/1.

I used it when I was running a 27T Trinity and a 19T Trinity at the track. It helped for sure and brought my temps down from 170F+ to 150F after a full run. The only basis the math provides to test the gearing is by the RPM of your motor. Trinity provided RPM stats, so at least I had that.
But the actual gear ratio doesn't include the motor rpm at all, and a 27T and 19T would be geared exactly the same according to the calculations. The calculations just takes the overall ratio and subtracts it from the tyre diameter and that's it. The rpms only come into play with the smoke screen used to "prove" the results. If you have a motor with a (theoretical, under no load) rpm figure of 20,000rpm and a motor with an rpm of 40,000rpm you would end up the identical "efficiency" percentages for both of them on the same gear ratio.

Brushed motors are geared correctly when you get the best performance from them. Overgear them and they will be slower coming out of corners, undergear them and they run out of steam before they are halfway down the straight. Brushless motors are different, generally if you overgear them they won't run any slower as they have more torque than brushed, and temperature is the only sure way of making sure you don't overgear them.

In the UK we have a Mardave class that runs 540 motors, at the top level if you are geared correctly the motor is too hot to touch when you finish the race and the performance drops off as the motor overheats, if you ran it geared for the '5 second rule' you would find you are too slow. This is why the top drivers all use peltier motor coolers to bring the temperature down to near freezing before the race.

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This is complete garbage! All you will get is either a cooked motor or a slow car.

I went through this same problem with my Durga and finally found the answer via the formulas below. This was the best way to target the optimal pinion for your gearing. It cannot however factor in the resistance of your motor (lower resistance = more heat), but it will let you know if your gearing is adding strain to the motor which will also produce more heat.

The formulas are mostly needed when using a brushed motor since heat and resistance is greatly reduced with a brushless motor, so your gearing can be more aggressive.

I used these formulas myself while I was still running brushed motors. I later switched to a Novak brushless and gearing became easy since they provided a gear ratio chart for their motors :lol:. You can always use this website if you want to create a bigger gear ratio chart for your DF03 - www.gearchart.com

P.S. If you have questions about the formulas, just let me know. I can figure out your gearing and post a chart for your car.

Solving the gearing problem:

What size spur gear should I run? What about the pinion gear? Well. When selecting the spur gear and pinion gear size, you need to understand that there is a ratio between the tire circumference (referred to as roll-out) and the final drive ratio. That ratio, in most cases, should be as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I am referring to the distance traveled by the tire in one revolution to the number of revolutions turned by the motor. In other words, if the motor turns X number or RPM's, the wheel will turn at Y RPM's, which is reduced by the final drive ratio. (A 32000 rpm motor with a final drive ratio 10.9893 will turn the tire at 2912rpm). For the sake of efficiency, the vehicle should be geared so that tire should travel approximately the same distance for every revolution of the motor, reduced by the final drive ratio. Heres how it works. Well use my RC10t3 as the example vehicle. The first thing to consider is the diameter of your tire. It is used to calculate the circumference of the tire. Multiply the diameter of the tire by pi. ( Ex: 3.25xpi=10.2101) Now, you need to consider the final drive ratio of your drive train. Begin by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear. This will give you your drive ratio. ( Ex: 87/19=4.5789). Now multiply your drive ratio with your transmission gear ratio ( Ex: 2.4x4.5789=10.9893 ). This is your final drive ratio.

Now the magic part. Subtract the final drive ratio from the roll-out of your tire . (Ex: 10.2101-10.9893= -0.77926) That is VERY close to a 0, but is geared a tad to the torque side of the motor ( anything below 0 is always geared towards more torque). Want more speed than torque? Redo your calculation adding another tooth on the pinion : ( Ex: 87/20= 4.35 ( drive ratio )x2.4 ( transmission gear ratio )= 10.44 ( final drive ratio ) Then subtract your final drive ratio ( 10.44 ) from your roll-out ( 10.2101 ) ( Ex: 10.2101-10.44= -0.2299 ) This is your optimum gear ratio, since it is closest to a 0 margin. Any ratio that is greater than 1 will run faster, but will overheat your motor, battery and esc, eventually damaging them.

How do we know this works? We can check out math by multiplying the roll-out of the tire, by the number of RPM's delivered to the tire, via the transmission. (Ex: Vehicle Final Drive Ratio is 10.44:1 and the roll-out of a 3.25" tire is 10.2101 " X 3065 rpm= 31294rpm) The motor's peak RPM is 32000, which means that we have less that 3% loss in efficiency from the motor, through the gear train.

Overgearing a vehicle will add to the speed of the vehicle, but it does so at a tremendous cost. The additional strain placed on the motor by the shorter gearing, will cause tremendous heat build up as the motor struggles to reach its peak RPM.

While this formula is not absolutely perfect, it does allow you to select a safe, and scientific starting point, to determine what is the best gearing combination for your particular vehicle.

This formula works best with 1/10 scale vehicles running stock to mid-modified motors. ( 27 turn to around 12 turn motors ).

Hotter motors 12 turn and lower will require you to reduce the ratio by as much as -1 or even lower to combat heat build-up.

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This is complete garbage! All you will get is either a cooked motor or a slow car.

Do you know some better math for gearing? :lol: I have always hoped to find something more accurate that can try to account for surface conditions, motor conditions, 2WD / 4WD etc. I searched for weeks to find the information I posted here. Sadly it is the best I have come across so far, but at least it was a little helpful.

The most fun I have had is calculating estimated MPH. I compared the math with my friends car and knew which pinion would make my car go a little faster than his at full speed (we both use the same motor).

Dan

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Math not required. It's all voodoo.

Do you know some better math for gearing? :lol:

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Math not required. It's all voodoo.

You might call it voodoo - I would call it experience :)

I'll try and help out here.

There is no "formula" for motor gearing. Every motor is different (even ones with the same wind, there are many different ways of constructing and tuning a motor), every track is different. Full-size car example - F1 cars run totally different gear ratios around Monaco than at Monza, even though the engines are the same at each track.

The two fundamentals in selecting a gear ratio are performance and motor temperature. If the car is sluggish, you are geared too high. If it tops out too soon, you are geared too low. If the motor is getting too hot (basic test with brushed is to put your finger on it and see if you can hold it there for a couple of seconds), you need to gear down. So better to start with a conservative ratio and gear up from there.

I generally run touring cars with 19T motors. Depending on the track (small indoor to large outdoor) I might fit a pinion ranging from 24T to 31T. There is no single gear ratio for a particular motor.

Oh, and don't even get me started on those "calculate speed from motor RPM" utilities. They are just as much nonsense. Peak no-load RPM is meaningless, power is what matters, and unless you can calculate all the other forces acting on the car (including wind and rolling resistance), you will never get a reliable speed calculation. Full size car example - my SEAT has a redline at 6500rpm or so. But it won't come close to that in top, there isn't enough power at those high revs to keep the car accelerating.

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Looks like the lowest I can gear is 25/79 as I can't even run the DF03 spurs (82 and 85) as they don't fit under the DF03RA guard, same mounting plate, different slipper guard, thanks Tamiya! PFFFFT!

Might just slap a CO27 in and be done with it, I could race a DF03 with a 25/85 ratio, surely a DF03RA with smaller rally blocks can handle 25/79

DF03 M Parts - 0115365

DF03RA M Parts - 9115236

The Spur Gear Cover on the RA M parts will not fit over the 82 or 85t spurs

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It does seem a bit strange that they remade the whole M parts sprue to change the gear cover while still including all the wing mounts, body mount and bumper from the buggies that the DF03RA doesn't use.

If you have the bigger spur gears try it without the gear cover, if it runs fine just get the buggy version to go over the bigger spur.

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Looks like the lowest I can gear is 25/79 as I can't even run the DF03 spurs (82 and 85) as they don't fit under the DF03RA guard, same mounting plate, different slipper guard, thanks Tamiya! PFFFFT!

Might just slap a CO27 in and be done with it, I could race a DF03 with a 25/85 ratio, surely a DF03RA with smaller rally blocks can handle 25/79

DF03 M Parts - 0115365

DF03RA M Parts - 9115236

The Spur Gear Cover on the RA M parts will not fit over the 82 or 85t spurs

Actually, there might be an aftermarket spur gear out there that is 100% compatible with your DF03 :lol:

I had a similar problem with my Durga when I bought a Novak 17.5 for stock racing:

The included spur was a 91T which limited my max pinion size to 24T before I ran out of room on the motor mount. Novak targeted the 4WD Gear Ratio of the 17.5 brushless to be 6:1. I did the math for the gearing and found that I would have to fit a 31T pinion to get a gear ratio of 6.03:1 :o. A 31T pinion would never fit and the best ratio I could get with the stock 91T spur and 24T pinion was 7.79:1, which means I would be undergeared and too slow.

I tried it anyway and guess what - I was undergeared and too slow.. The motor would barely get warm.. I would never be able to get the optimum gearing unless I could change the spur! Problem is, Tamiya doesn't make any other spur for the Durga.... What could I do???

I found the solution is a spur made by Team Associated (Kimbrough slipper gear). Turns out that Tamiya basically copied the spur design for the Associated RC10B4 (right down to the octagonal slipper pad mount). Associated made the same spurs in 78T, 81T, 84T and 87T varieties. I bought their 81T spur and everything fit perfect. Tamiya's slipper pads fit, the center shaft was the same, I even measured the center thickness of the spur with a caliper.. It was identical, so I didn't even have to add or remove shims from the center shaft..

I recalculated the gearing math for a 81T spur and got a target pinion of 28T (5.94:1) - the closest match for the recommended 6:1 gear ratio.

Did everything fit - heck ya!

I did a full run of the motor. Speed and torque were awesome and the motor finally warmed up.

The motor was still cool enough that I could push the car to the next pinion, a 29T with a 5.74:1 gear ratio. The 29T was ideal. Motor temps were perfect, everything was great!!

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Well took the rally car out today at the local offroad track about 27 degrees celcius ambient, geared the 15 turn at 25/78 (figured I'll see what happens, it's only an Ansmann Clash and probably half dead)

Felt pretty slow from the get go, after 8 mins the car stopped, smoke from the back.

Out with the trusty Temp Gun

117.7 degrees CELCIUS!

That motor goes in the bin, open to ideas now!

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Actually, there might be an aftermarket spur gear out there that is 100% compatible with your DF03 :lol:

I had a similar problem with my Durga when I bought a Novak 17.5 for stock racing:

...

Did everything fit - heck ya!

The DB-01 is designed to use industry standard spur gears, such as found in the B4. It also uses 48dp spurs. The DF-03 doesn't use the same spur gears and to fit a B4 gear in a DF-03 slipper clutch needs B4 slipper pads and you also need to enlarge the hole in the centre carefully to keep it centred. You then would need to ditch the DF-03 pinions and replace them with 48dp ones.

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it's only an Ansmann Clash and probably half dead
You said you had a 15 turn motor, I would never class an Ansmann Clash as a motor :lol:

You'll get more speed and way more torque from a 19 turn motor than a 15 turn Clash. Personally I would go for the Team Checkpoint Money motor. For a cheap motor there's the Venom Fireball range, although I think it's worth spending the extra on a good quality motor.

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You said you had a 15 turn motor, I would never class an Ansmann Clash as a motor :lol:

You'll get more speed and way more torque from a 19 turn motor than a 15 turn Clash. Personally I would go for the Team Checkpoint Money motor. For a cheap motor there's the Venom Fireball range, although I think it's worth spending the extra on a good quality motor.

I have put in a Trinity Monster Stock 27 turn now, kept it at the 25/79 gearing. Do you think that will heat up as well?

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Took it out with the Monster Stock, I think progress is being made, motor came off at 45-50ish celcius which is acceptable. Hope to improve that with some new brushes and a com clean as this motor hasn't been touched in about a year.

I figure a CO27 should run cooler, we gear them a bit harder in onroad racing and they definately run cooler than the Monster Stock in TC racing.

Just wondering if there is anyway to get a fan to force some air into this thing.

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