Drivetrain

Enormous forces want to be controlled. A little theory and a few calculations improve performance.


Table of contents

  • Introduction
  • Calculate gear ratio
  • Calculate overall gear ratio
  • friction
  • Unwanted movement
  • Differentials

Introduction


It is important to understand that it is not enough to simply let a few gears run together. With extremely high speeds, power and torque, nothing can be left to chance. By building a stable and robust drive train, you can achieve very good performance and a very long service life of the parts.

It is essential to know which translations you can work with. Calculating them is child's play.

Calculate gear ratio


The gear ratio influences acceleration, top speed and the load on the engine. An incorrect gear ratio can also destroy the engine. Therefore, you should choose the right translation in advance.


The gear ratio is influenced by the gear sizes. But also, very important, on the size of the wheels.


The gear ratio is super easy to calculate. Just that driven gear divided by the driving gear. In this case, the driven gear has 24 teeth and the driving gear has 8 teeth. Don't be confused, the result is always given in relation to one revolution ( :1 ). In the case of the example calculation, three turns to one.


Overall gear ratio


Of course you also have to calculate the entire translation. This isn't rocket science either.

Simply multiply the translations together.

In the case of the First Prototype this is:


3 x 1.57 = 4.71


In general, it should be said that the overall translation should be shorter. Say 5-6:1 . An additional fan is installed in the First Prototype to cool the engine. Without it, the engine would get so hot that surrounding parts would be deformed by the heat.



If you want to calculate the entire drive train including the wheels, things get a little more complicated. Here I make it a little easier for myself and use the calculator on the website Kfz-Tech.de.


https://www.kfz-tech.de/Biblio/Formelsammlung/Fahrschnell.htm


It is important to note that you can only enter the theoretical speed of the motor. The actual speed of the engine would have to be measured beforehand while driving. You can assume that the engine can reach around 80% of its full speed, with a total gear ratio of 5:1.




Example:

T-Motor F60 2020 KV

2020 KV = 2020 u/min / 1V


12V x 2020 = 24240 u/min


80 % = 19392 u/min



19392 rpm is a realistic value that we can use. Of course the speed increases or decreases if you use a larger or smaller battery. More about batteries, motors and more Performance parts


shorter translation


  • more acceleration
  • less top speed
  • less temperature on the engine
  • the car accelerates more abruptly and is therefore more difficult to control

longer translation


  • less acceleration
  • more top speed
  • more temperature on the engine
  • the car accelerates more smoothly and is therefore easier to control

friction



must be avoided at all costs!!!!!!

Excessive friction puts additional strain on the drive train and costs a lot of performance. It's not just good lubricants and ball bearings that help here. With ball bearings you should pay attention to the following:

  • good quality of the ball bearings
  • only the required amount of ball bearings,

they also have friction


It's the same with the gears, you should only install the number of gears you need. All parts moving towards each other create friction.



Unwanted movement


When it comes to the drivetrain, you can't leave anything to chance. In particular, you should assume that you... The power of the engine is always massively underestimated.

If the drive train is built too unstable, movements will occur which will greatly reduce its longevity or even lead to the immediate destruction of individual components. It is also possible that parts become entangled and therefore performance is lost.



Example:


The main shaft requires at least 3 bearings. At least one on each differential and another one in the middle, as close as possible to the gears. If you leave them out on the gears, it could happen that the gears push apart and no longer mesh properly. Which means that the gears would break very quickly. The main shaft could also start to oscillate. This massively reduces the longevity of the installed ball bearings and gears. It also costs performance and causes unrest in the car, which can actually affect the performance of the chassis.



Differential

28 teeth differential, you can use it but should be treated with caution. Accelerating unconditionally doesn't work; it would break immediately with an output of 150 W.

The new 22 tooth differential has the potential to transmit a lot of power. But not without a small additional part.

The differential tends to dismantle under load and immediately wear away the frame in which it is installed. With the thrust washer from Fast Bricks Rc, this problem is history.

I haven't tested the metal differential from Metall-Technic-Parts yet, and there's a reason for that. Basically, the idea of having a metal differential is a good one.

First of all, you have to say that the forces acting on the small gears are relatively small, but I still don't think the design with 3 small gears is good. With 4 gears, all gears would support each other and always run smoothly. However, there are only 3 installed here, which can lead to them being pushed apart on one side. This brings with it the danger that the gears can become entangled. The differential could partially lock or even break

The differential from Zenestore is a full-fledged RC differential. The differential body and the input shaft are mounted, so there is no more play and extremely smooth running. The housing is completely closed, which significantly minimizes maintenance. All gears are made of metal and enormous performances are possible. The closed differential body makes it possible to use different greases, which opens up the possibility of using a percentage differential lock.


Conclusion:

Actually exactly what you need. But unfortunately Zenelego still has quality problems. No two differentials are the same. This means that correct adjustment is simply impossible with an all-wheel drive. I hope that Zenelego gets this under control soon. Finally, it should be said that all parts from Zenelego, like Fast Bricks Rc, are handcrafted and are a small series. This makes it extremely difficult to ensure affordable, good and consistent quality.

Share by: