RC Tips Page !!

Metal Gear Servos

Installation Tips

Something that I hear about on a regular basis, would be owners complaining that the servo mounting tabs on the servo case have broken. Many times this is a result of improper installation. A servo that handles a function such as throttle and braking typically sees only a fraction of the stress that a steering servo will encounter. So while it's fine to mount a throttle/brake servo straight to the truck's chassis, different measures are much more appropriate for the steering servo.

Most servos include some rubber insulators and brass eyelets. These are used in situations where the servo may encounter heavy hits or shock-loads. The picture below shows a set of these sitting alongside a servo.

To install the insulators and eyelets, you simply squeeze a rubber insulator into the mounting hole. Then, once the insulator is in position, push an eyelet through the hole. You'll do this for all four mounting holes. The picture below shows a servo with the insulator and eyelets installed on set of mounting tabs so you can see the difference.

The end result is that the servo will now be able to move slightly when subjected to an impact. This will place less strain on the servo mounting tabs. While it's still possible that a hard enough hit will damage the servo's case, it will take much more abuse than it would without the insulators and eyelets. One last factor to keep in mind is that due to the cushioning you have provided, the servos response may be subdued slightly but an experienced racer may prefer to still mount the steering servo straight to the chassis.

"Most of the problems with rechargeable batteries
can be traced to misuse"

HOW CELLS ARE DAMAGED

Sustained high-current overcharge and cell polarity reversal (during discharge) are the main killers of NiCad and NiMH batteries: If a high charge rate is used, it is essential to terminate charge when the cell is full. If this is not done, the temperature and pressure within the cell will rise quickly as the charging current is dissipated as heat. Both NiCad and NiMH cells have internal vents which will open to allow gas to escape and prevent explosion of the cell. In the case of NiCad, the gas released is oxygen, while a NiMH cell will vent hydrogen. The gas that is lost can never be replaced, which means that the lost cell capacity which results from a severe overcharge is not recoverable. It is never wise to rely on the cell's vent as a failsafe, because they often corrode overtime and can not be assumed to be absolutely reliable. Avoiding abusive high-current overcharge can only be ensured with a well-designed charging system that responds to the signal the battery gives when fully charged. Cell polarity reversal is a potential problem with any series-connected string of cells: as the battery is discharged, the cell that goes down to zero volts first will continue to have current forced through it by the other cells. When this occurs, the voltage across the fully-discharged cell is reversed. A cell that has current forced through it with a reverse voltage across it will heat up very quickly and vent gas in a similar mode to that described for the sustained overcharge, with the same resultant damage.

LI-ION: HOW CELLS ARE DAMAGED

The biggest problem with the Li-Ion battery is the ease with which it can be damaged during use: The Li-Ion battery carries a very large amount of energy in a small package. Combined with the fact that the internal resistance is fairly high, you have the potential for a very dangerous product: If the cell is accidentally shorted, it could get hot enough to burn a user (and possibly explode). The makers of Li-Ion cells handle the explosion threat by designing the case of the cell so that it will "die with honor", and not explode in someone's pants pocket if the battery hits their car keys. More important, the actual battery terminals are simply never allowed to reach the outside world. The only manufacturer presently shipping Li-Ion batteries for consumer products does not sell single cells, only battery packs. Contained within the pack is circuitry that isolates the battery power leads from the outside world if excessive current is sensed, pre-venting battery damage and protecting the user. Another easy way to destroy an Li-Ion battery is by discharging it too far. The Li-Ion cell should never be allowed to drop below about 2.4V, or an internal chemical reaction will occur where one of the battery electrodes can oxidize (corrode) through a process which can not be reversed by recharging. If this occurs, battery capacity will be lost (and the cell may be completely destroyed). A similar process will occur if an Li-Ion cell is charged to too high of a voltage. If current is continually forced into a fully charged cell, internal corrosion can take place which will reduce cell capacity (possibly completely). For this reason, Li-Ion cells can not be trickle charged for extended time periods without cutting off the current when full charge is reached. Sustained charge currents (even a few µA) can damage the cell if allowed to run continuously.

AGE-RELATED FAILURE MODES

NiCad: After a period of time, the insulator within a NiCad battery often develops holes which allow the cell to grow crystalline "shorts" that provide a conduction path between the positive and negative electrodes of the cell (which basically shorts out the cell). If this happens, you may have to blow open this short with a high current pulse before the cell will again accept charge (a process sometimes referred to as "zapping"). A leaky NiCad cell will always have a high self-discharge rate and will re-grow internal shorts if left on the shelf without some kind of trickle charge. The annoyance factor of batteries that go dead quickly often prompts users to throw away leaky NiCad batteries, even though they may still be able to give nearly full A-hr capacity during discharge. NiMH : The NiMH cell (according to the manufacturers) is not supposed to be prone to developing internal shorts like a NiCad battery. User feedback (so far) on NiMH has been good, with no major problems reported. Li-Ion: The Li-Ion battery got off to a weak start, as there were many failures in the first batteries shipped. However, the addition of the internal protection circuitry inside the battery (and increased knowledge about the failure modes) has improved this. At present, there are no known problems which appear significant enough to prevent Li-Ion from successfully penetrating the high-end consumer market

How to stop an engine?

There are five primary methods of shutting an engine off. Other people may have slight variations on these five methods, but the basic concept should be identical. A combustion cycle in an engine takes place in the following sequence:

Crank shaft is turning
Vacuum action draws in air
Air is mixed with fuel in the carburetor
a hot glow plug ignites mixture
exhaust exits the engine

So if we can stop any of these from taking place, the engine will stop running. Lets take a closer look at what each one does.

For an engine to continue running from one cycle to the next, its crank shaft must remain turning. Everything else could be working just fine, but stopping the crank shaft immediately stops the engine. However, stopping the crank shaft of a running engine is easier said than done. If the engine is at a low idle, the crank shaft can be stopped by jamming the tip of your shoe against the flywheel. In most vehicles this is rather awkward because the only way you can access the flywheel is to turn the vehicle upside down. Also, if you are trying to stop a engine that is stuck running wide open, you can forget about it; It is potentially developing too much power for the crank shaft to be stopped. So while it is certainly possible to stop an engine this way, it is mostly not recommended.

Since an engine needs air to run, we can stop the engine by blocking the carburetor air intake with a finger. Doing so essentially suffocates the engine, and most engines will stop within half a second or less. This method is far safer to accomplish than trying to directly stop the crank shaft. However, since the carburetor intake is covered by the air filter and the vehicle's body, it is often difficult to pull this off in a hurry. So if you want your engine stopped quickly, this may not be the ideal way to do it.

To make a combustible mixture, air is mixed with fuel inside the carburetor. Pinching the fuel line right before it connects to the carburetor deprives the engine of the needed fuel. And without fuel, the engine will not run. However, there is usually some fuel that has pooled in the engine crank case and it is enough to keep the engine going for a short period. As the left over fuel is burned, the engine runs increasingly leaner. This results in an increase in the engine RPM, which can be unnerving to someone who is trying to stop the engine. But soon enough, the engine RPM will quickly drop and then stop completely. It can take anywhere from 3 to 10 seconds to stop an engine this way, and it is usually very difficult to access the fuel line in a hurry. So this method is all but useless in trying to stop an engine in a hurry. What this method is good for is to prepare the engine for storage. Fuel left over in the engine after a day of running will attract water, which results in corrosion. Burning off the excess fuel will reduce the chance of corrosion and extend engine life.

RC model engines are called glow engines because they need a heat source in the form of a glow plug to ignite the fuel for each combustion cycle. Removing the glow plug, therefore, will stop the engine immediately. With that said, you should block this permanently from your memory. No one ever does its, and it is the least convenient way to stop an engine. It's simply too impractical.

As air and fuel is burned, the exhaust gas expands and rushes out of the exhaust port of the engine. With a properly tuned exhaust pipe, the pressure wave from the previous combustion cycle helps pull the exhaust gas out. When the exhaust gas leaves the cylinder, it draws in fresh air and fuel to be burnt for the next combustion cycle. So if we place a finger over the exhaust tail pipe opening, the pressure inside the tuned pipe will build up, preventing the exhaust gas from leaving the cylinder in the next combustion cycle. And if exhaust gas doesn't leave, fresh fuel and air doesn't enter. And without fresh fuel and air, there is no combustion, and the engine will stop. This chain of events transpires almost immediately after you cover the tail pipe opening. It takes at most one full second for every engine I've ran with to be stopped this way. And since the exhaust tail pipe is easy to access, this is the ideal method of stopping an engine in a hurry.

I am sure this is a bit more than you needed, but I think understanding the reasons behind why things work the way they do will help you enjoy the hobby more.

How To Take A Corner

This is the perfect type of corner on which you should practice, A hairpin teaches you throttle control and steering control, once you have mastered this type of corner and you can hit it the racing line every time, you can't be far off brilliant!

In order to do that, when you go into the corner take it as wide as possible, this enables you to carry more speed through the corner. Aim to cruise instead of breaking it reduces the chance of rolling since the buggy can slow down at its own rate. Only brake if you are going way to fast. The acceleration out of the corner is another important factor that you must get right, to soon and you go wide, to late and you loose to much speed. the picture above shows what you should be aiming for. Also you may notice in the picture that the buggy clips the corner after the apex, this helps the car accelerate away much better due to the straighter line it has on exiting the corner. A good practice for this type of corner is a figure of eight

Combined corners such as S-bends are surprisingly easy to negotiate Depending on the sharpness of them, the one pictured below is relatively fast, but the principles for taking them are the same.

You should aim to keep as tight a line as possible on the bend. Its quite easy for people to overtake you if you go just a little wide. To do this, pull out to the edge of the track meaning you have the shallowest possible possible corner to take, also when you come into the corner don't brake as hard, in fact if its like the bend above don't break at all just go to half or three quarter throttle. This gives you plenty of speed through the corner. On the second corner accelerate a little earlier than you normally would and use the whole width of the track to get out of the corner.

RC Tips Page !!

Metal Gear Servos

Installation Tips

There are five primary methods of shutting an engine off. Other people may have slight variations on these five methods, but the basic concept should be identical. A combustion cycle in an engine takes place in the following sequence:

Crank shaft is turning

Vacuum action draws in air

Air is mixed with fuel in the carburetor

a hot glow plug ignites mixture

exhaust exits the engine

How To Take A Corner

This is the perfect type of corner on which you should practice, A hairpin teaches you throttle control and steering control, once you have mastered this type of corner and you can hit it the racing line every time, you can't be far off brilliant!

Combined corners such as S-bends are surprisingly easy to negotiate Depending on the sharpness of them, the one pictured below is relatively fast, but the principles for taking them are the same.