Part 2, covering Suspension, Drivetrain, Wheels and Tyres, Maintenance and Upgrades.
1) Do I really need oil filled dampers? Just plain springs will work fine too, right?
Indeed springs can help a car negociate bumps and so, but they are very limited. For best road contact you want the shock to move as lightly as possible, to react fast to bumps etc, but don't want the vehicle bouncing up and down several times after encountering an obstacle. With simple springs, that is what you get.
There is an option to use thick grease on the shock rods, called friction grease. These friction dampers already work better than just simple springs but the grease used tends to be very sticky to hands etc, almost like glue, and the damping action still leaves to be desired.
Oil filled shocks provide the best possible handling. The thickness of the oil affects the damping, as well as the shape of the piston, and the amount of holes and size of the holes in the piston. This way you can make the shock's response vary from silky smooth to much tougher. Quality shocks use o-rings to seal off the oil-reservoir, so these can't leak easily. To get an even better seal, you can use "Green Slime" or a similar product. But even if you have to fill up oil shocks on a regular basis, and sometimes remove all the old oil, and fill with new, the much improved road/terrain handling makes it all worth it.
2) Can I use any oil for shocks?
Although other oils might work, often these don't offer a stable damping response over a wide temperature range, and some oils may even damage the plastics and o-rings used. Silicone shock oil doesn't have this risk, and has stable viscosity over a wide temperature range. It comes in many thickness ratings, expressed in CST, CPS or WT. Problem is their relation is not linear. With the WT standard it can even be that one brand's 30 WT is not as thick as another brands 30 WT. CPS/CST doesn't have this problem, so it's easier to stick to that. To get an impression, soft, thin oils are up to 350, than till about 700 you have the medium thick oils, and till 1000 are the "hard" oils.
3) My car handles pretty badly, it bumps all over the place. Do I need to get new shocks?
If you already have oil filled shocks, and assuming you have tyres that provide good grip on the surface you run on, it could be the shocks just need some tweaking/cleaning. With the spring removed from a damper, does the piston move smoothly up and down? If you feel something binding, perhaps the piston rod is bent, or some dirt has found it's way into the damper and is now stuck between piston and shock body. If needed, remove the oil, and see how the piston moves then. It should move very freely, the resistance should come fully from the oil. As most pistons are molded plastic, it's possible burs are still present on the edges of the piston, increasing friction between the inside of the cylinder and the piston. Best way to check this is to remove the piston and rod from the shock, and insert the piston from above in the cylinder.
If that is ok, and the handling is still pretty bad, what thickness of oil are you using? RTR vehicles are often supplied with thicker oils, as this will prevent the car from bottoming out during the average abuse of a beginning driver, which often includes high jumps, as the driver is testing the car's limits. A hard setup will protect the bottom plate from scratches etc, but can also negatively affect the car's handling. Try a light oil and see how it goes with that, or if you have the choice between shock pistons with more or less holes, try those with more holes, allowing the oil to move more freely from one side of the piston to the other.
What can also help, if available, is mounting the shocks more to the outside on the suspension arms. This creates more "leverage" for the shocks, and they will respond to smaller bumps. This will also affect ride height or ground clearance, so keep an eye on that.
4) I'm going to get new oil shocks, but can't decide between the various types...
So, if you do need new shocks, either because the current ones are worn, broken, or your car currently has friction shocks or simple springs, you will find out there are different types. First there is the choice of metal vs plastic. Where with other car parts it's often a debate whether metal will be better than plastic, with shocks this debate is quickly settled. With plastic shocks there is always the risk of the shock caps popping off on a big impact, and the metal shock body tends to have less friction between it and the piston. Furthermore, some metal shocks have coated insides for even further reduced friction, like the "velvet" coating Kyosho uses, or Titanium Nitride coating, to name a few.
Then we have several types:
For 1/10 scale this means a shock body diameter of around 12 mm, single shock body. Quite capable, for years this was the best possible option. RTR cars that come with oil shocks, are often fitted with these.
"Big Bore" shocks
As the name suggests, the shock body is bigger in diameter than regular shocks. The idea is that this improves damping, and it usually does. Beware though, sometimes the label "Big Bore" is just used for marketing, and one company's Big Bore shocks are the same as another brand's regular shocks...
These shocks have a second oil reservoir, "piggybacked" on the main cylinder. Apart from looking a bit weird at first sight, it's supposed to have an advantage over regular and big bore shocks. The idea is that, even though silicone oil has quite constant thickness over a wide temperature range, the oil in the shock can get warmer during heavy action (remember all the impacts on the shocks are dampened with friction, in this case friction in a fluid, and where friction occurs, there is thermal energy aka heat) and will get thinner as a result. As with Piggy Back shocks you have more oil in the shock, it takes longer for it to heat up. But the advantage over regular big bore shocks, and even normal diameter shocks, is limited. Besides, if alu shocks are used the free air flowing over the shocks during running, will also help to prevent a signifcant temperature increase.
Apart from the limited advantage, if any, these are harder to (re)fill properly, and take up more space, sometimes limiting mounting options. So probably best left alone, unless you like the looks better than other shock types, and don't care much about the disadvantages.
5) My car pulls wheelies all the time, or does a 180 turn unexpectedly. It's very twitchy on the throttle...
Well, it could be you just need some more practice, just like with a real car. Especially a 2WD vehicle, with most weight to the rear, and combined with a powerful brushless motor and lipo battery, can be very twitchy. If possible, you could try to lower the ESC's start power, often called "punch" to soften throttle up. If your transmitter has expo-settings, you could also make the throttle response curve more gentle.
Apart from these electronic solutions, it won't hurt to look at the drive train. Is the slipper clutch adjusted properly? (See Part 2 "Drivetrain" for tips how to adjust the slipper clutch properly) If the rear shocks are too rigid, either from having thick oil, tough springs, or high spring tension setting, or a combination of these 3 causes, the rear is also more prone to act as pivot point. Lessen the pre-load tension on the springs, use softer springs, or thinner oil, so that the rear will be allowed to kick down a little upon acceleration, this absorbing part of the "blow" when you hit the throttle.
If that won't bring enough improvement, you could shift weight forward by moving the battery if possible, or add extra weight up front. Or get a wheelie bar, or fit a less powerful motor, as a car prone to making wheelies is often somewhat overpowered.
Some extra info:
Besides these basic tips, there is much more to setting up the suspension. It affects cornering, braking, jumping characteristics, etc. There are some excellent guides on the internet aobut this area, surpassing my expertise on the matter by far, so I'll post a few links here when I found these again.
Update: this link gives a nice overview of setup options: http://users.telenet.be/elvo/
(click on "Quick Reference Guide" for a list of options and their effects)
No matter how powerful your motor is, how much amps your battery can deliver, etc, it all doesn't mean much if you can't get that power to translate into forward motion. Tyres play a big role, as well as the earlier covered suspension, but the drivetrain is also very important. Here are a few things to observe.
6) What's the purpose of a differential (or diff), and how does it affect my car?
When a car makes a turn, the outside wheel has to cover more distance, as it runs over a bigger radius, than the inside wheel. This means the outside wheel has to spin faster than the inside wheel. With a rigid axle, that would not be possible, and this would stress the axle, wheels or tyres, especially on a high traction surface. The solution is a differential
, it allows 2 axles to be connected and driven, but still be able to rotate at different speeds. As a result, no driven wheels are stressed, as each wheel can rotate at the speed needed to make the turn. This rather old video does an excellent explanation of the effect: http://www.youtube.com/watch?v=yYAw79386WI
Besides helping in turns on high traction surfaces, the diff can also have some drawbacks. If on a 2WD vehicle one wheel loses all contact with the ground, the diff can allow it to "freewheel" and as a result the car will lose all traction and stop. This is something to be avoided. To do this there are 2 options, depending on the type of diff (short for differential) that is used.
Let's first cover gear diffs
, that use an array of bevel gears (altthough other gear setups are also possible, but this type is most common in RC vehicles) to get the diff-effect. If you want to limit the "freeness" between both sides, thick grease, or filling the diff with very high thickness silicone oil (if the diff is sealed with o-rings against leaking) will limit the amount of independance between each outgoing axle. This will make the diff behave more like a rigid axle, but in lower grip conditions, that often offers better traction.
Another popular diff type in RC is the ball diff,
that uses small balls clamped between two plates, to allow different rotation speeds between inner and outer wheel. Although these also use grease, this is not to finetune the amount of diff-action, but just for lubrication. The pressure between plates and the small balls can be adjusted to allow for more or less "freeness". This is less messy than using oil to fill a diff, and there is no need to take the diff apart to replace the oil, when adjustment is needed. But it may take some practice to fine tune this type of diff to best performance. Whereas with the gear diffs, if you know what thickness of oil is recommended for a certain car, you already have a good reference as starting point.
Finally, in very low grip conditions some cars offer the option to temporarily lock the diff, so it behaves like a rigid axle. When the car is back on high traction surfaces, the diff is better unlocked, for better handling under those conditions.
7) What is meant with "shimming the diff" and what is the benefit?
Shims are thin rings, sometimes as thin as 0.1mm, that are used to reduce play. These are used on wheel axles mostly, but can be applied on more places. If a car uses gear diffs, it's likely these will be made up with bevel gears. When under high stress, if there is play on the axles that the gears are on, this could make the gears move a little, and have worse gear mesh. This can damage the gears, and cause the diff to fail. As a precaution, you could take the diff apart, and use the right size shims to reduce this unwanted play. Don't overdo it, the gears should still be able to turn quite freely, but a little extre resistance compared to an unshimmed diff is ok as well. After some use, the diff will smoothen up a little anyway, as the gears start to wear in to each other.
It may take some time to get it right, but it will certainly enhance the diff's life expectancy. Some companies, like 3-racing, have conveniently packaged multiple thickness shims in one package, in that case 0.1, 0.2 and 0.3 mm, giving you more options. If a 0.3 mm is too tight, and a 0.1 too loose, you can use a 0.2 instead, and keep the 0.1s for moments where only a very thin shim is needed,
What's the purpose of a slipper clutch, and how do I set it properly?
A slipper clutch, or short, slipper, is used to make the coupling between spur gear and rest of the transmission less direct. As the name suggests, it allows some slip. This will shield the transmission from sudden high torque, like when accelerating full throttle. Most common way to achieve this is by having the spur gear "sandwiched" between 2 plates, with a thin layer of special somewhat rubbery looking material (these discs are called slipper pads) between the plates and spur surface. A spring loaded nut supplies the pressure and allows adjustment.
Like the ball diff, this slipper clutch takes some attention to adjust properly. Set it too tight and it will not help with sudden impacts on the drivetrain, increasing the risk on stripped gears, etc. Set it too loose, and the car will not be able to pick up speed fast, and accelerating will feel like driving on ice. The excessive slipping of the clutch can also cause the slipper pads to heat up and get burnt, rendering these unusable.
A common way to adjust the slipper clutch, is to first tigthen it fully, then start loosening it up. A general rule here is that, when giving full throttle from standstill, it should only slip the first few metres. You can often hear the slipper being active, as a sort of "squeal" coming from the transmission.
There are other methods, and as with most adjustments, after a while you tend to develop a feel for it, and you get to a good setting faster.
Wheels and Tires
Do RC wheels need balancing, just like on real cars?
With the lighter weights involved in an RC car compared to a 1:1 scale, this is often overlooked, or discarded as making only a marginally small difference. But in fact it can have much more effect on a car's handling and wear. Just pick up your car, and add throttle. Most likely you will feel vibrations, and probably can even see the ends of the suspension arms oscillate more or less with various throttle settings. This is mostly due to inbalance in the wheels. Remove the wheels, and perform the same test, and you should feel absolutely no vibrations, except from the gears.
Though with the wheels touching the ground they will have less freedom of movement to vibrate, inbalance in the wheels will make the holes in the suspension arms wear out faster, as well as all other pivot points in the suspension, including the steering and the attached servo. It can also cause screws to vibrate loose, though loc-tite should prevent that, it's clear that it's better to address the source of the vibrations, instead of countering it's side effects.
There are special tire balancer tools, in which you can suspend the tire, and check it's balance. When an inbalance is found, you can try to remove material on the heavier side, or add mass on the opposing side. When adding weight, make sure these are secured properly to avoid these weights flying of during a run.
A cheaper method for checking balance, while still fairly accurate, is taking a caster block, with bearings and axle, and mount the wheel. Hold the caster block pinched between your fingers, with the tire facing upward, then give the wheel a spin with your free hand. A well balanced wheel will need very little strength to hold the caster block, but one with inbalance will feel like it wants to break loose, and you will need to increase your pinch hold to keep it steady. A slight inbalance will probably not show up here, but only as you hold the wheel in it's normal position, but it will probably add little benefit when trying to eliminate this final minute inbalance. Final check is, as we started out, mount the wheels on the car, preferably one at a time, test for vibrations, add another wheel, check again, etc. When done with care, the result will be a car that runs without noticable vibration for it's entire throttle range, running more quiet, with less wear and more stability.
What tyres do I need?
Unfortunately there is no straight answer to that. What tyre will perform best often depends on conditions on the track or area where you drive, and also weather conditions. Generally, if you run offroad, you are likely to need more thread on the tyres, whereas a flat surfaces requires a more smooth tyre with less thread.
Besides the thread type, the hardness of the rubber also greatly affects tyre performance. A softer rubber compound will offer more traction, but on a high grip surface that might be too much, and the car will be more likely to do a griproll, meaning the car has so much sideways grip, the car just rolls over in a fast turn. Another drawback is that a softer rubber compound tends to wear faster. No problem if you have a money-tree in the backyard, and if you race in competition, you simply can't avoid having multiple tyre sets, for different race conditions. But most of us will probably be looking for a more cost effective solution, so a tyre that will offer good performance and will last more than a few runs.
Finding that tyre is usually a matter of trial and error, asking what more experienced drivers use. Personally, for casual driving, bashing, I prefer block pattern tyres, which offer decent traction even when using harder rubber compounds. Or V-pattern rally tyres, like these:
The latter have softer rubber compound than the block pattern tyres I use, but because there is more contact patch with the ground, the tyres don't wear fast at all. I'm still running my first set, whereas spike tyres of similar rubber softness would have been slicks by now...
How do I remove worn tires and fit new ones?
Sooner or later, tires will wear down, and require replacement. The easy way is replacing the wheel and tire, and buy pre-glued tires. But this limits your choices, and can be pretty expensive.
Another option is using tires that fit so tight around the rim, that there is no direct need to glue these to the rims as well. Especially when you don't run competition, this could do nicely.
The third option, which should be the most durable, is to remove the worn tire, and glue on a new one. To dissolve the glue holding the tire to the rim, there are 3 main methods:
1: Soak in Acetone. This fluid tends to dissolve CA-based glues, which are commonly used to glue tires. Fill a cup large enough to accomodate a wheel and tire with it, and put the wheel in. Make sure you do this on a well ventilated area, as it's a volatile fluid. Using gloves is also advised.
Apart from the health precautions you need to observe, there is a chance the plastic of the rims also gets affected by the soaking process, which can result in color chances, or even deformation.
2: Baking. Using a hot air oven to make the glue become soft, and remove the tire of the rim. Be careful of getting burned, and also here is the risk of damage to the rims, as the warm plastic can also easily be deformed.
3: Boiling: Putting the wheels in boiling water can make the CA glue become brittle, and as a result the tire can be peeled off the rim. Beware of the tire insert soaking up the water, which will be released as you handle the tire, and is still close to boiling temperature. Also, there is a risk of deforming the plastic of the rims while these are still hot.
Once you have succesfully removed the tires of the rims, the next challenge is to glue the new ones on. RCG member Paul Onorato posted an excellent tutorial on how to glue tires. Even though it covers SCT tires, the principles hold for most other tire types as well. You can find this tutorial here: http://www.rcgroups.com/forums/showthread.php?t=2138417
What tools do I need to service my car?
This partially depends on the car, but one tool will prove handy for a wide variety of cars, the cross wrench:
It contains 4 different size wrenches, 7mm, 5.5 mm, mm and mm. These will fit the wheelnuts, shock nuts, and some other too. Some brands include one with their kits, or RTR packages, if you don't have one, get it asap!
From here on the brand of car plays a role as some brands use Philips head screws (with a "plus" on the head) while other brands will use hex exclusively. Common hex sizes used are 1.5 mm, 2.0 mm and 2.5 mm, although inch sizes are also common in some parts of the world. Whatever type of screws your car uses, make sure you get a matching tool, and beware of low quality cheap drivers, that often have such soft tips, you risk wrecking the screw's head, and won't be able to remove the screw the normal way afterwards. A few dollar spent extra here, will pay off quickly, as you don't strip heads, and are spared for the frustration that comes with this.
Do I need to clean my car after every run?
Though the initial answer would be "yes", as maintenance after every run will most likely keep the car in top condition, it's possible to save on time invested in this, and still have good lifespan for the car's parts. The decision whether to clean things, and even take apart certain sections of the car, depends much on the conditions you ran the car in. If you drove on a paved road, which was mostly clean, perhaps you will find a thin layer of dust on the tyres, and maybe the body shell, but apart from that the car didn't suffer much. In that case, a quick dusting off will usually do.
However, any surface involving water, requires if possible, immediate action. Especially when running on the beach, as salt water and sand are a car's worst nightmare. It can corrode bearings, and the sand tends to find it's ways everywhere, (just like when you have been on the beach ;-) ) and especially the drive train doesn't respond well to some grains of sand jammed between the gears.
There is a little debate about how to treat the bearings, some say it's just a matter of wiping dry, and adding a drop of oil. Some prefer to use a cleaner spray, like WD40, motor cleaner, etc, so flush the bearings, and then re-oil these. The main drawback of this method might be that cleaner residue stays behind in the bearings, or you flush out the valuable thick grease, that was put inside the bearings to ensure longest possible lifespan, and replacing it with a thinner oil, that doesn't have the same protection capabilities of the stock grease.
But that aside, you should do something, if you just put the car away, don't be surprised if the next time you take it out, some or more bearings have seized up, or are creating a lot of drag and noise.
Suppose you avoided the car getting wet, but drove on a dusty surface, so there is a bigger chance some moving parts have gotting very dusty as well. You can take everything apart, or do a simple test which gives a good indication if the dust entered the drive train. Take the pinion off the motor, and move the car forward and backward manually. If you feel extra drag, or some "grittyness" when moving the car back and forth, there is a good chance some dust/sand is compromising the moving parts, so you have to find out where it comes from.
If the car seems to be running smoothly still, don't be tempted to use compressed air to clean it, as you risk blowing sand/dust into the transmission, so the car may actually be worse after cleaning. A soft cloth, and a toothbrush are much more safe. Perhaps not as convenient as with compressed air, but it saves bearings.
Apart from cleaning, some areas of a car require periodical attention, just like a real car would. Be sure to check on a regular basis for loose screws, nuts and bolts. Check if the suspension is still moving smoothly, and for signs of shocks leaking. A tell tale here can be dust sticking just below the cap, indicating some oil flowed from there, and caused the dust to stick to the cylinder. If you suspect a serious leak, refill the shock, and test it. Sometimes the o-rings at the bottom can leak somewhat. Tighter rings will help, but will also cause extra friction, so the shock can't move as smoothly as it should. Applying a little shock sealant, like the oddly named "Green Slime" can give that extra leak prevention, without hampering the shock's performance.
Check if the wiring and plugs are still ok, no conducting wire parts exposed, where these can cause short circuit, and if the wiring is still secured well away from moving parts, like a drive shaft.
If you didn't check for it during cleaning, remove the pinion from the motor-axle, and move the car around manually, to feel if the transmission is still moving freely, with no uneccesary drag.
Caring for brushed motors
In case you are still running a brushed motor in your vehicle, it will need special care. Due to arcing between the brushes and the commutator (which we will call "comm" from now on), a dark layer will form there, reducing the contact between these parts, and as a result the motor will become less powerful, and heat up faster. If you have a motor with consists of a sealed can, fixing this can be hard. You could try some comm/motor cleaner, and/or try to wipe the commutator surfaces with a cottom swab, but this is not easy. If you bend open the locking tabs on the rear of the motor, you can get better access to the brushes and comm. Still, this can be tricky, and usually closed can motors are cheap, so you might wonder if it's worth the trouble.
If you have a motor with removable rear section, also called the "endbell", there are more options to keep it in top shape. You can remove the springs that hold the brushes, slide these out, and clean the brush and comm surfaces with rubbing alcohol, or comm cleaner. You could also remove the endbell, for even easier access to these parts. For best performance, the comm should be trued on a special lathe. If that is not handy at the moment, or you don't want to spend the money on it, you can use very fine grain waterproof sanding paper. If you pinch the comm between thumb and indexfinger, with a piece of sanding paper wrapped around the comm. Then slowly rotate the axle while trying to apply even pressure, creating a "poor man's lathe" polishing the comm's surface. A real lathe will always be better, but when done carefully, this can work out pretty well.
After this polishing, clean the brushes and comm surface. With the comm, be sure to clean the gap between the copper colored sections, so no dust from sanding remains there. This can be done by carefully moving the tip of a knife through those gaps. Rebuild the motor, and let it break in again. If performed well, the motor will run much better than before, faster and cooler.
First, an upgrade that any car will benefit from, are ball bearings, if these are not already fitted. Some brands try to be economical and either fit plastic bearings (very bad) or self oiling bronze bearings (somewhat better) in their cars. These give higher resistance, and more wear than ball bearings and limit performance. Before considering any other upgrades, check if your car has ball bearings, and if not, fit these, for better speed, lower wear, and longer run time on your batteries.
Are metal parts better than plastic?
Often it is thought that replacing plastic parts with metal versions, is always better. Often the "bling" of the metal parts already makes a car look faster, more sturdy, etc. But despite the looks, it's wise to use metal parts with care. Plastic usually has some flex, this helps to absorb the impact of a crash. When a plastic parts is replaced with metal, the impact will get transferred to either another section of the car, or the metal part will bend. Also, metal parts, even when made from aluminium, are still typically heavier than their plastic counterparts. This means less performance of the car, and more energy to dissipate when the car hits something.
So, think well before replacing a plastic part with a metal one, if it will really improve the car, unless looks are more important than durability.
What's the purpose of CVDs aka Universal joints?
Getting the drive power to the wheels on a vehicle with independent suspension requires a flexing axle. A simple way to get this is a "dogbone" and drive cups.
Simple, and easy to take apart. Dogbones tend to be a little more noisy, especially as the suspension arms moving up, and the angle between drive cup and dogbone increases. Apart from that, sometimes dogbones can "pop out" under extreme stress, and the u-shaped openings in the drive cups wear out sooner or later.
CVDs or universal joints have an advantage, one of the drive cup/dogbone connections is replaced with a direct coupling, like this:
This type of drive axle will cause less resistance under an angle, which is mostly convenient on the front of a 4WD vehicle, where the wheels make multiple angles with the drive axle, as these need to steer. But these can also be used as upgrade parts for the rear wheels, making the drive train a little more efficient.