How to Set Gear Mesh on an RC Car in 3 Easy Steps

Nearly all RC Cars and Trucks contain meshed gears. Iit is important to properly set gear mesh for optimum performance. Improperly set gear mesh can cause a list of problems with your setup. The good news is that setting the gear mesh of your RC car or vehicle can be done quite easily. The gear mesh is adjustable in order for you to have the ability to change the gear ratio by using different pinion and spur gears.

Setting Gear Mesh in 3 Easy Steps

What you will Need

  1. Tools to adjust the Gear Mesh on your RC vehicle.
  2. A piece of standard size paper cut to 10mm x 50mm (1/2in x 2in) (Used for larger gears)

Step One – Loosen the Gear Mesh

Most RC Car’s allow you to adjust the gear mesh by adjusting the location of the motor. Find the location where you may adjust the location of the motor by loosening the fasteners that lock the motor in position. Once the motor is loose, be certain it is free to move in the direction that would allow for gear mesh adjustment.

Step Two – Set the Gear Mesh

Slide the 10mm x 50mm piece of paper in between the pinion gear and the meshed spur gear. Bring the two meshing gears together and apply a small amount of pressure to jam the piece of paper.   Using paper works best when you have a larger set of gears. For example 32 Pitch or Metric Module 1. (Mod 1)

If you have gears that are smaller, using a piece of paper will provide too much of a gap. In this case, bring both the pinion and spur gear together until it feels like the gears bottom out on each other. Relax the pressure and bring the pinion gear/motor away by a very small amount. The aim here is to bring the pinion gear away by about 15-20% of the overlapping distance. This will leave you with around 80-85% of overlap between the gears.

Step Three – Tighten the Gear Mesh and Check

The final step is to securely fasten the screws that allow you to adjust the gear mesh. Once everything is solid and locked in to place, quickly check the overlap of the gears. Optimal mesh is achieved when 80-85% of the gears are overlapped. There should be a small amount of space between the meshing gears where you can see light through. The 15-20% gap is important for proper gear mesh.

Symptoms of Improperly Set Gear Mesh

Improperly set gear mesh can cause issues within your RC car. There are only 3 possible outcomes after you set the gear mesh. The first outcome is that you have everything set correctly and nothing further must be done. The second outcome is that you have set the gear mesh too tight. The final outcome is setting the gear mesh too loose. In either case, it is important to make the correct adjustments in the gear mesh for best performance and reduced wear.

Gear Mesh Set too Tight

If you happen to set the gear mesh too tight, you may hear a grinding noise or in general excessive noise coming from the meshed gears. Your motor may be overworked due to increased load caused by the friction of the meshed gears. Lastly, a tight gear mesh will cause pre-mature wear of the gears. Typically, the pinion gear is made of metal and the spur gear is made from a form of plastic or nylon. In this case, the plastic or or nylon gear would wear out first.  To prevent further damage, stop the vehicle and adjust the gear mesh to be not as tight.

Gear Mesh Set too Loose

Gear mesh set too loose will also show signs and symptoms. However, with loose gear mesh, you do have to pay more attention to the signs as they are more subtle. One of the first signs of a mesh set too loose is backlash. Backlash is when one gear is able to rotate a few degrees until contacting the meshing gear forcing it to rotate. Backlash causes wear when you must switch the direction of motion frequently. Wear is produced by each gear accelerating and slamming in to the next gear when a small amount of momentum is built.

Another symptom of gear mesh set too loose is complete destruction of the gear. Unfortunately, this symptom will not provide you with much of a warning. I’ve gone through a few spur gears in my day from this one alone. A good way to prevent this is to check the mesh of the gears before driving your RC Car or Truck.

Lastly, after several runs of your RC Car or Truck, take a look at the spur gear. Determine if there is significant wear occurring at the tips of the teeth on the spur gear. Excessive wear at the tips of the teeth is a sign of gear mesh set too loose.

 

Use These Gear Mesh Tips to increase the performance of your RC Vehicle, transmission and reduce wear.

 

Prop Thrust and Pitch – What do they do?

It doesn’t matter if you fly RC airplanes or drive RC boats. These vehicles use a propeller ( prop ) and both are affected by each term, Prop Thrust and Prop Pitch Speed.

When referring to prop thrust and pitch speed, they both contribute to propeller performance. To be effective, a prop must deliver an adequate amount of thrust and pitch speed. Let’s look at what defines each term.

Propeller Pitch and Thrust

Propeller Pitch and Thrust

Prop Thrust Definition

Propeller Thrust is defined by the amount of force the prop can create along the axis of rotation. This force is directly translated in to the motion of an RC boat or plane. Thrust is a function of the size, rotational speed and pitch of the prop.

Prop Pitch Definition

Propeller Pitch is defined as the  distance that the propeller would move forward during one full rotation of the blades through its travel medium.  The value of pitch is typically provided in inches or millimeters and assumes no slip.  Pitch is increased on a propeller by increasing the angle of attack of the propeller blades.

Prop Pitch vs Prop Thrust – What do I Require?

Prop thrust is required for any application in order for the motor / prop combination to do work. This is also true for prop pitch.  In order to select a propeller for your application you would need to understand what your application is designed for to begin.

An airplane or boat that is designed to travel at slower speeds, would benefit from a propeller that delivers a high amount of thrust. Pitch speeds for a slow moving RC vehicle is not as critical. At the other end of the spectrum, if you have an RC boat or airplane that travels fast, pitch is quite important.

In general, fast moving vehicles have a smaller amount of drag than slower moving vehicles. This natural  marvel makes it much more simple for us to select the best propeller combination.

Prop Thrust is generally created from maximizing the diameter of the propeller. Pitch does contribute to thrust, however diameter more efficiently creates thrust.

Selecting the Correct Propeller Pitch

Let’s set an example that our RC Airplane should travel at a speed of 120 km/h. If we know the general speed of the RC airplane we can then select an appropriate pitch value. In order for our airplane to hit 120 km/h, the pitch speeds of the propeller must exceed 120 km/h. If we can not exceed 120 km/h in pitch, it is certain that our RC vehicle will not be capable of hitting 120 km/h. The primary reason for this is that there will always be slip in a prop. The slip will not allow us to attain the pitch speeds of a propeller. You can visit the RC Airplane Calculator page in order to calculate pitch speeds of a propeller.

Selecting the Correct Diameter Propeller

The next step as a continuation of the above example is to select the diameter of our prop. In order to accomplish this we must know one significant point in propeller selection relating diameter and pitch of a prop. A high angle of attack can make the propeller stall, becoming less effective at lower speeds. For an airplane this starts to happen when our diameter to pitch ratio starts to get smaller than 1.25:1. As you decrease the diameter/pitch ratio, the propeller performs poorly at low speeds. This scenario is not ideal when low speeds are an absolute requirement.

With this said, we can select an appropriate propeller diameter that will allow us to hit our thrust goals. Increasing the diameter of the propeller will increase the thrust potential of the prop while decreasing the diameter will decrease the thrust potential of the prop.

Prop Thrust and Pitch Summary

In conclusion, both thrust and pitch are very important. Thrust is required in order to overtake the amount of drag that is produced by the RC airplane or boat. However that thrust has to be made at the speed in which the vehicle would be travelling at.  This is where pitch speeds of the propeller is critical. Be certain to select a propeller combination that has enough pitch speed to achieve the speed goal of the application. A proper balance of both will produce the results that you are looking for!

 

 

How to extend ESC wires correctly

Extending ESC wires can harm the ESC if not done correctly. We explained the sort of phenomenon that is responsible for the troubles. That can be found here in an article titled, “Why extending ESC wires can be harmful.”  Bottom line is that the inductance of the battery input wires can destroy your ESC. You can either extend the motor to ESC wires or you can follow what is below.

How to extend ESC wires on the Battery Input Side

It is possible to extend the ESC wires by adding in a few components near the ESC. The component you must use are capacitors. Capacitors are used in parallel on the ESC battery input wires. These capacitors are best positioned as close as possible to the ESC. They are wired directly across the positive and negative terminals of the ESC in one location.                                                                                                                                                                                                      Affiliate Link to Castle Creations Capacitor Bank

It is important to not distribute them along the length of the ESC to battery wires. Doing so will not provide any benefit to the system. In addition, placing the capacitors close to the battery will not be efficient as the battery acts as a much larger capacitor. The inertia in the form of current gets worse as you move down the wires towards the ESC.

What Size and how many Capacitors are required

The capacitors that you will require are to be low ESR( Equivalent Series Resistance) and low impedance. These capacitors tend to be cylindrical in shape and because of this are commonly known for being cylindrical capacitors.

Cylindrical capacitors are polarity sensitive. When you wire them up, be certain that you know which terminal is positive and which is negative. Wiring capacitors to the wrong polarity will certainly cause failure.

The voltage of the capacitor must be higher than that of the maximum voltage of the battery. It is best to also have some head room here as the pulses generated from operation can actually increase the voltage load (higher than the max battery voltage) of the capacitors. Having capacitors that are much higher in voltage is no problem.

The amount of capacitance that you must add when extending ESC wires are 460uf for every 100mm or 4 inches of wire. Keep in mind this is one run of wire and does not represent a double run of wire.

Example of how to Extend ESC Wires

How to Solder Capacitor Bank to Extend ESC Wires

How to Solder Capacitor Bank to Extend ESC Wires

In the example above, the capacitor bank is soldered at the positive and negative terminal posts to the ESC wires. The battery wires to the ESC have been extended by 4 inches. In order to compensate a 460uf capacitor must be used. It doesn’t matter if you require one capacitor or three capacitors to get to 460uf or more. You can place capacitors in parallel to add up to the sufficient amount.

Extending Wires from ESC to Motor

There is no problem extending the wires on the motor side. No risk to the motor or ESC is taken. The worst thing that can happen is possible interference from these longer wire runs. In order to combat the interference, 3 twists per inch of the 3 wires leading to the motor with help.

Why extending ESC wires can be harmful

Did you know that extending the wires on your ESC can actually be harmful for your ESC? Yep, it’s true, extending wires on the battery side of the ESC can put a lot more stress on your ESC. This is for brushless motors.

Cutting ESC Wires - Water Hammer Effect

Cutting ESC Wires – Water Hammer Effect

Why extending wires can be harmful?

Extending your battery wires are only harmful on the battery input side of the ESC. The battery is the source of power that feeds the ESC current at a specific voltage. The ESC is responsible for sending the correct pulses of current to the brushless motor. In order to accomplish this, the ESC must be in sync with the exact rotational position of the motor. When the correct winding position matches up with the correct pole of the permanent magnet on the motors rotor, the ESC sends a pulse of current that allows the motor to rotate to the next position where this process repeats.

During this process the current that is passed by the ESC turns on for a split second and then shuts off for a split second. This repeating process is continuous as long as the motor is on. Now imagine the power coming from the battery rushing toward the motor and then all of a sudden it is shut off. We can think of a similar situation occurring with water within our own homes.

The water hammer effect

The water hammer effect is what many would more recognize within your own home. Take the same approach as we just covered but apply it to your faucet at home. Or even another high volume water valve. When you run the water at maximum velocity through one of these valves and then rapidly shut that valve as quickly as you can, you are inducing the water hammer effect within the pipes that feed that faucet or valve. Depending on a number of different factors within this plumbing in your home, you may very well hear a “hammer” type sound within the pipes.

We hear this hammer type sound as the water is forced to come to a complete stop. Upon coming to a complete stop, a shock wave is produced that ends up travelling back down the pipes.

This type of effect can be very damaging. Especially in areas where there is a very high volume of fluid travelling in pipes and abrupt changes. Although a water hammer in the home can be damaging if it is bad enough, water hammers throughout the house usually don’t cause catastrophic damage.  Either way, you don’t want them.

Water hammer in our ESC

The exact same thing happens within our ESC’s. This ripple effect caused within the wires of the ESC on the battery side, must be dampened in order for proper ESC function. You can see large capacitors on the input side of every brushless ESC. The job of these large capacitors is to smooth out the different pulses that exist in the main input circuit. These capacitors can be seen in the image above. Just the tips of the capacitors are outside of the heat shrink.

However, even large capacitors have a maximum capacity. If these capacitors are pushed hard they eventually can fail. If these capacitors fail, your ESC is destined to fail.

You never want this to happen. If it does, you are left with an ESC that can’t even be used as a paper weight since it will be burnt to a crisp.

Can you safely extend wires on an ESC?

The quick answer is yes. You can increase the length of wire between the ESC and motor quite easily with nothing special added. However, extending the length of the wires from the ESC input side to the batteries is possible but takes a bit of effort to complete successfully and safely. We will cover this in another article.

Best C Rating for RC LiPo Battery

Selecting the correct LiPo battery pack for your RC vehicle is not as easy as just selecting the cell count. One of the most important parts of the correct battery pack selection is also considering the C rating. What is the C rating? Well let’s take a look!

What is the C Rating?

All LiPo battery packs have a C rating associated with them. Actually, they have not just one C rating, but a few C ratings that we will discuss shortly. A C rating is a value given to the LiPo battery pack that refers to the maximum discharge rate of the LiPo.  Examples of C ratings could be anything between 30C to 65C. Numbers outside of this range are possible as well. LiPo’s typically have the C rating marked right on the front of the LiPo pack. Can you spot the rating on these packs?

2X 4s 4000mAh with a C Rating of 45C

2X 4s 4000mAh with a C Rating of 45C

 

How to calculate Max Discharge using the  C Rating?

The maximum discharge rate of the LiPo is highly dependent on the capacity of the battery pack. In general the larger the battery pack in terms of capacity measured in mAh, the higher theoretical maximum continuous discharge rate you should expect. With this being said, the capacity of the battery pack is part of the calculation. We first take the capacity of the battery pack in mAh and convert this to Ah. Next we use the maximum continuous discharge rating in order to perform the calculation. Take these two values and multiply them together.

If we look at the image above consisting of a 4000mAh 4s pack, it has a C rating of 45C. Firstly, 4000mAh is converted to 4Ah. We then take 4Ah and multiply it by 45C. The resulting value is 180 Amps.

4Ah x 45C = 180Amps

Our Turnigy Graphene pack is capable of providing 180A continuously according to the rating provided by the manufacture.

Check out this page to help calculate battery pack specifications.

Other C Ratings of a LiPo Battery Pack

There are other C ratings that can be found on LiPo battery packs that aren’t typically spoken about. The second C rating that is also quite important, is the rating provided for charging a LiPo battery. This C rating is specifically for the rate at which you can charge the battery pack at.

Charge Rate C rating

There are many chargers on the market these days that are able to charge at a high charge rate, significantly decreasing the amount of charge time. In order to be certain you can charge your pack quickly, you must verify the charge rate using the charge rate C rating.  When LiPo’s first came out, typical charge rates were known as 1C. Typical C ratings for charging in today’s day is anywhere from 2C to 15C where 15C charge rates are crazy!

The Turnigy Graphene pack in the above example has a charge rate of 10C. To determine the maximum charge rate, we first convert the pack capacity to Ah from mAh. 4000mAh is equal to 4Ah. Next we multiply this value by the charging C rating. 10C x 4Ah = 40 Amps maximum charge rate.  Keep in mind that this is an extremely high charge rate, in fact I typically do not charge any faster than 3C. An absolute personal maximum is 5C.

Peak Discharge C rating

The last and final C rating that you may come across when looking at LiPo battery packs, is the C rating for maximum peak discharge rate. The peak rating may or may not appear on the battery advertised. Typical peak ratings could be anywhere between 50 to 100% more than the rating for maximum continuous discharge.

What C rating is required for my Application?

The correct answer here really boils down to budgets, battery pack weights/sizing and required discharge rate. Having the battery pack with the highest C rating is always best for the power system and battery pack health.

It is best to have a discharge rate overhead of 30%. If you work out a maximum power system discharge of 100 amps. Your battery pack should should deliver at least 30% more or 130 total amps. Never match system draw to maximum continuous discharge rates of the battery pack.

2s 860mAh with a C Rating of 35C

2s 860mAh with a C Rating of 35C

For example, I would select this 860mAh at 35C for a load that will discharge at a maximum continuous current of 23 Amps.

35C x 0.86Ah = 30 Amps
30 Amps / ( 1 + 30%) = 30 A / 1.3
23 Amps

Having a battery pack that can deliver 1000 Amps for a motor that will only use 10 Amps may seem like overkill, and it probably is. However, there is no reason for concern that the battery pack could over power the motor. Keep in mind that a load only pulls the amount of current that it requires.

In conclusion, the best C rating for your pack is a value that will allow 30% overhead in discharge rate, fits your budget, and is the correct size and weight for your application.

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