DOMOisCOOL

*Cough*TC3*Cough*

Most TC3's I've seen are pretty loud. But that's just me.

losispeed

hum, My evo runs nearly as quite as my Losi XXX-S...

IMO the diffrence between shaft and belt should NEVER be the primary concideration or even minor factor in which car you buy..
The things that make a car fast are,
1. Driver....
2. The overall quality of the car.. I.E. a TT01 vers an Xray..
3. The Tuning done to the car.
4. The time and effort that was spent in putting the car together.

So IMO a belt driven 415 is going to be just as fast as a shaft driven EVO IV...

MR JOLLY

When the barracuda goes round are local track i take a set off ear defenders with me

Dragonfire

iTrader: (1)

I love the "shaft has more punch" theroy. For anyone that understands your physics, shafts transfer 80% (at best) of their power to the outdrives and the other 20%+ tries to force the diff out of the car.

Its simple.... all else being equal belt generates more grip with less speed, a shaft generates less grip but has more speed. Torque steer is only a prob if you lack grip/stability

Having driven many of both, its the driver and his setup that makes a car fast....

andsetinn

Shaft drives in motorcycles all have lot of slop, you'll never see serious racing bike with shaft drive. (Warning, big can of worms just opened.) Serious racing bikes all have chains, belts are not strong enough, shafts have slop. But rc cars can not be directly compared to motorcycles.

Racing4Evo

iTrader: (2)

You're right you did open a big can of worms (ala BMW dakar rally bikes which by the way are 2 wheel drive!) And even though most racing bikes use belts(chains to be exact), all racing cars use shafts.

Let's leave it alone.

SammyXp

Flawed logic. Yes, noise is energy, but not all wasted energy is manifested as noise. As a matter of fact, only a tiny fraction of wasted energy is noise. The vast majority of energy lost in any drivetrain is usually heat due to friction.

Where did you get these numbers? You're saying that over 20% of the energy transmitted through a shaft drive car is lost to heat (friction due to side loading on the ring/pinion)? With the average power output of a modified motor easily exceeding 200-300 watts, you're talking 40-60 watts of mostly heat! While I don't have any data that indicates what the true drivetrain efficiency is for a typical shaft driven car, I can promise you that it is not 80%.


IF this grossly oversimplified generalization were true, then all you are saying is that the cars are geared differently. Top speed has little relevance on drivetrain efficiency. It relies mostly on gearing. But if drivetrain A is more efficient than drivetrain B, it can be geared higher, without increasing the load on the motor and electronics.

Cyclonus

If one was better than the other why would any of the manufactures waste their time manufaturing a car with an inferior drive train? If one were truely faster than the other surely all the manufacturers would know this. Why would half of them still keep persuing designs using whichever one was inferior? Both are more or less equal. I dont really see any advantage from one to the other in really any cricumstance. Sure maybe you cant break a belt in a shaft car, but the pinion can come loose from the shaft. Either way your in the same boat. All the top manufactures have good designs and you can win with any of them. With some it's probably a little cheaper but you can win with any chasis as long as you have the skills and have the necessary support equipment.

Mabuchi540

True not all wasted energy is manifested as noise but the noise you do hear is wasted energy....or something like that sorry my bad didn't word it right the first time.

Dragonfire

iTrader: (1)

So true.. every bit counts. Everyone has noticed that their car is slower with a damaged spur (aka rock damage). You may notice that there is also noise....

Energy does not have to be lost as heat. A shaft drive by its gear design transfers energy at a small angle. If you revisit your "forces in two dimensions" chapter, you can work it out graphically.. nice and easy.

The best attribute of shaft is it low friction which gives great top speed for open tracks.

Everyone likes a different "feel" in their setup ,and if you have driven both (shaft/belt), you will have "felt" this difference. This is prolly the best thing a shaft has going for it.

GundamWZero

iTrader: (4)

Then just buy two cars; a shaft driven one and a belt driven one. Set them up for whatever track condition you feel that it is most dialed in. I am pretty sure we all have at least a shaft driven and a belt driven car (at least I do).

Case closed......

fatdoggy

If you've never tried a shaft or belt just try out a friends cars next time your at the track. There is a good chance they will let you as long as you can wheel a car. If you break the car you buy them lunch and pay for the parts. It's worth it too feel the difference imo.

SammyXp

The noise is just a side effect of an inefficient drivetrain. While you've got your high school physics textbook cracked, look up the energy calculations for sound power. See how much energy is required to achieve a particular sound power level. The car would have to be deafeningly loud in order for a significant part of drivetrain loss to be attributed to noise.
Trust me - I was doing diagnostics on a project recently at work and was trying to trace energy loss to noise and no matter how I spun the calculations, I could not do it.
But you are correct that a noisy drivetrain is often an inefficient drivetrain. The sound coming from the car isn't where the energy is lost, though.


While we are humoring vector mechanics - think about what that lateral force component is doing. Yes, the ring and pinion has thrust - and the lateral force is used up where? As friction in the bearing. This force is obviously small enough to not require a thrust bearing in addition to an axial bearing. Whatever small lateral load is created in the ring gear can easily be supported by the axial bearing as a side load. With clean bearings, the heat generated by friction as a result of this force component is nearly negligible.
If you want to look for inefficiencies in a shaft drivetrain, study losses in bevel (ring/pinion) geardrives. These are straight-cut bevel gears and might see an improvement in efficiency if they were helical or even hypoid gears. But the fact that the designers of these drivetrains chose straight cut gears indicates that losses were small enough that the added complexity was not deemed necessary.

SammyXp

Did a little further probing, for those that aren't yet bored to tears...
A straight cut bevel gear generally has an efficiency in the range of 96%-98% (source: An Explanation of Right-Angle Gearboxes).
A straight cut standard spur/pinion gear mesh generally has an efficiency in excess of 99%.
Overall drivetrain efficiency can be estimated by multiplying each gear mesh efficiency throughout.
In a shaft drive RC car, there is a straight spur/pinion mesh and then a straight bevel gear ring/pinion mesh.
Therefore efficiency for each axle is:
0.99 (spur) x 0.96 (ring) = 0.95
This is neglecting any losses in bearings and driveshaft couplers.

Cobra81li200

Not really, helical gears adds friction compared to straight cut gears. They are used when we want to decrease the stresses on the teeth, by the fact that they increase the number of teeth in contact at a time (straight cut gears have 1 tooth in contact, while helical have more, depending on cos beta). In ay case, the best efficiency is for straight cut straight gears, and a change in direction will always result in losses, even minimal.

On a belt, the losses comes from the energy needed to bend the belt when it comes around the pulley. Thus, bigger pulleys results in a more efficient drivetrain as the angle at which the belt bends is lesser, but you also have to take into consideration the linear speed of the belt, which depends on the diameter of the diff pulley.