Wednesday
Jun052013

Ride height adjustment

The ride height should be kept to a minimum; this will keep the centre of gravity of the car as low as possible and maximising cornering speeds. The ride height should ideally be between 4 – 6 mm (1/8"-3/16"), but on bumpy tracks or where regulations dictate otherwise run the car a little higher. Check regularly to compensate for tire wear which can be rapid on some tracks.

Adjusting the front ride height

A-arm spacers cab be mounted under A-arms of the front suspension. Placing the front A-arms block lowers the chassis (less ride height) and conversely putting them above raises the chassis, giving more ride height.

Adjusting the rear ride height

Three molded different pairs of rear axle bearing holders have been included in the kit, they are all off-set to give 6 different rear axle height settings. Optional Available are six pairs of rear axle Hard Anodised Aluminium bearing holders. With these settings it is possible to fine tune the ride height with different kind of tire sizes.

Remove the rear axle and fit the appropriate pair of bearing holders to each end of the rear axle tube, complete with ball bearings and put the rear axle back into place. Do not forget to re-mesh your pinion and spur gear. Always use the same height setting on both sides of the car otherwise the rear axle bearings will lock up.

Wednesday
Jun052013

Tweak! (left to right balance of the car)

One of the most important factors when racing an R/C on-road car is ‘tweak'. If a car is tweaked then the car will turn differently in left and right hand bends.

Although purposely tweaking a car is often advantageous when oval racing, for other forms of racing it is generally best if the car handles exactly the same in both left-hand and right-hand turns.

A car becomes tweaked when the grip or weight is not balanced between the left-hand and right-hand wheels. This may occur in several ways:

  • The chassis assembly could be twisted; his is no longer common in modern cars, but should be checked after major crashes.

  • The tires on each side of the car could be different sizes; the outside tire generally wears more quickly than the inside tire. To prevent this problem swap the tires from the left-hand to the right-hand side after every couple of races. Or, use a tire truer to true the tires if available.

  • The suspension or ride height may not be set the same on each side of the car. Check springs, tweak adjuster settings and ride height settings.

  • Steering movement may be different on the left-hand and right-hand sides.

  • Tires may be giving different grip levels. Check and replace any that seem to have different firmness on the left or right.

  • When using tire additive it is possible to accidently tweak the car by applying different amounts of additive to each tire – be careful!

  • Finally its possible for the car to feel tweaked if the suspension does not move freely. Check that the power wires to the motor do not restrict the rear suspension movement and check that all ball joints move freely. 

Saturday
May182013

International handling and shipping rates

Shopping online is great. The global catalogue of products to search and research is endless and is a major source of enjoyment itself. The only real drawback about buying products from the global online marketplace is the additional cost of handling and shipping, which is typically very expensive. Making matters worse is the fact that online shops do not subscribe to a standardised price list for handling and shipping, even when the goods are coming to Australia from the same country.

Therefore, to keep costs as low as possible, its important to know which online shops offer the best handling and shipping rates. The purpose of this post is to create a dynamic (constantly updated) list of online shops abd the handling and shipping rates they offer.

Before I start comparing the handling and shipping costs of online stores, I will set a comparative benchmark by listing the Consumer Flat Rates (rate including packaging) of the United States Postal Service (USPS) and the Hong Kong Post (no acronym used).

United States Postal Service (USPS) to Australia (US$)

Express Mail® 

  • International Flat Rate Boxes/$79.95 (Max. 9 Kg)
  • International Flat Rate Envelope/$44.95 (Max. 1.8 Kg)

Priority Mail®

  • International Large Flat Rate Box/$77.95 (Max. 9 Kg)
  • International Medium Flat Rate Box/$59.95 (Max. 9 Kg)
  • International Small Flat Rate Box/$23.95 (Max. 9 Kg)
  • International Flat Rate Envelope/$23.95 (Max. 1.8 Kg)

Hong Kong Post to Australia (US$)

  • Rate for weight not over 500g/$12.75
  • Rate for weight over 500g up to 1kg/$18.40
  • Rate for every additional 500g for weight over 1kg up to 5kg/$4.25
  • Rate for every additional 500g for weight over 5kg/$4.12

Comparison of international handling and shipping rates

The list below lists the international handling and shipping rates of online shops I have come across (I will update this list whenever I can).

The test order is a Team Associated TC6.1 World Touring Car (TC6.1) kit whenever possible. If not possible, I will order a similar size kit from another brand.

1) RC Mart/TC6.1 - EMS Express (3-4 days)/$47.76 & CP (7-30 days)/$30.74

2) A Main Hobbies/TC6.1 - USPS Express/$51.99 & USPS Priority/$44.99

3) TQ RC Racing/TC6.1 - USPS Express/$64.99 & USPS Priority/$49.99

4) Reflex Racing/TC6.1 - USPS Express/$72.88 & USPS Priority/$55.66

Saturday
Apr272013

RC car setup 'rule(s) of thumb'

The first rule of thumb for setting up a new RC car is to start with the manufacturers recommended setup. This is the best default point from which to innovate from.

The second rule of thumb is to change one combination at a time. A single change to an existing setup makes it easy to test the new setup and attribute the results to the correct change. If you decide to implement the change, you run your next change from this point.

Sunday
Apr212013

Key gearing calculations

The useful gearing calulations below were published by 'dragnse7en' in RC Universe.
 
Internal Transmission (Gear) Ratio:
To calculate a car's gear ratio, you need to be familiar with the type of drivetrain it has. 2WD RC vehicles typically have a single one-speed transmission. 4WD vehicles also usually have a one-speed transmission, and are gear and propeller shaft driven or belt and pulley driven. Multiple speed transmissions can also be calculated for gear ratios, if attention is paid to the things mentioned below.
 
If the vehicle’s manual didn’t provide a gearing table in its contents, then you’ll have to take apart the transmission to count the number of teeth on each gear and write it down.
 
Here are the names of the gear you will need to count:
 
1. Diff Gear (diff pulley for belt drives)
2. Counter Gear (center pulley for belt drives) 
 
The counter gear/ center pulley counts as any component that runs on the same shaft or axis as the spur gear. Note that some shaft driven cars won’t have a counter gear close to the spur; they would be the gears that mesh directly with the diff gears.
 
Now that the number of teeth on the gears or pulleys have been counted and written down, we can plug the numbers into an easy formula to get the gear ratio of the car’s transmission.
 
Internal Transmission (Gear) Ratio Calculation:
X = diff gear/ pulley
Y = counter gear/ center pulley
Z = Internal Transmission (Gear) Ratio
 
X / Y = Z
 
Gear ratios are typically expressed in Z:1 (2.055:1 for example).
 
For example, one of my cars has a 36T diff pulley and a 16T center pulley. I should get a gear ratio of 2.25:1
 
36 / 16 = 2.25
 
For the sake of simplicity, we’ll use Z above to get the car’s Final Drive Ratio (FDR). It’s another simple formula, using the difference between the spur and pinion gear, and getting a product from Z, the car’s gear ratio. Again, count and write down the number of teeth for both the spur and pinion if you don’t know what they are.
 
Final Drive Ratio (FDR):
Spur gear = A
Pinion gear = B
Power Output Ratio (External Gear Ratio) = C
 
A / B = C
 
Finally, multiply the power output ratio by Z above, the gear ratio:
 
C * Z = FDR
 
The FDR is also typically expressed as a :1, or to one ratio (4.75:1 for example).
 
Rollout:
To calculate the rollout of the car’s gearing, you will need to measure the tire’s diameter in standard inches. Once that’s written down, calculate the circumference of the tire by multiplying it by Pi (3.14). One example would be a tire with a 2.44 inch dia. would have a cir. of 2.44 inches.
 
Divide the circumference of the tire into the car’s gear ratio, and you will get the potential rollout of the car.
 
Tire circumference = A
Gear ratio = B
Rollout = C
 
A / B = C
 
For example, using the numbers we already have:
 
2.44 / 2.25 = 1.08
 
To convert mm to inches, divide the mm by 25.4 (for example, 62mm = 2.44 inches, or 62 / 25.4 = 2.44).
 
Saturday
Apr202013

Glossary of key gearing terms

The explanations below were written by Gary Katzer and published on the losi.com website.

Gear Ratio – A gear ratio is the relationship between the number of teeth on two meshed gears. This relationship is expressed mathematically. For example, if one gear with 50 teeth is driven by a gear with 20 teeth, the gear ratio is 2.5:1. You would calculate this by dividing 50/20 for a total of 2.5. In an RC Car, you have 2 different ratios you'll need to work with to achieve the proper gearing for a specific application and goal. The first is the external ratio and the other is the internal ratio.

Internal Gear Ratio – The gear ratio of a vehicle's transmission gears separate from the pinion and spur gear ratios. The internal ratio is a fixed number determined by the manufacturer of your vehicle.

Ball Differential – A differential that utilized a series of ball bearings, thrust bearings, differential rings, tensioning spring and thrust washers. When going around a corner, the tire on the inside will need to rotate more slowly while the tire on the outside will need to rotate more quickly. Ball differentials can be infinitely adjustable, but require more maintenance (distance traveled).

Clutch Bell Gear – The gear that mounts to the crankshaft of a nitro- or gasoline-powered engine that is used to drive the spur gear.

Differential Gear – The gear that drives and houses the differential components. Typically the differential gear is mounted on the bottom of a transmission case in a 2WD vehicle.

Gear Differential – A differential that uses gears instead of ball bearings and allows wheels to rotate at different speeds. When going around a corner, the tire on the inside will need to rotate more slowly while the tire on the outside will need to rotate more quickly. The differential compensates for this difference in distance traveled.

External Gear Ratio (or Power Output Ratio) – The gear ratio of the gears that are visible or outside of a transmission case. This is the ratio of the pinion and spur gear.

Pinion Gear – A small gear that directly attaches to the output shaft of an electric motor.

Spur Gear – The large gear mounted to the top shaft of your transmission in an off-road vehicle, the center differential in an 1/8-scale or 4WD Short Course Truck or the main lay shaft in an on-road vehicle. The spur gear is driven by the pinion gear or clutch bell.

Pitch (AKA Pitch Diameter) – In countries that do not use the metric system, pitch refers to the number of teeth on a gear with a 1-inch pitch diameter. The higher the number on the pitch, the finer the tooth profile is. The finer the pitch, the more efficient the gear; however, since they have less material, they are often more prone to stripping if the mesh is not set properly. The more coarse the pitch, the less efficient the gear will be; however, they are also more durable and less susceptible to damage. 48 pitch is the most common pitch in RC, however, 64 pitch and 32 pitch can also be used.

Final Drive Ratio (FDR) – The gear ratio of the entire drive system in a car or truck. This includes the internal gear ratio of the transmission and the external gear ratio of the pinion and spur gears. You can calculate this ratio by dividing the spur gear tooth count by the pinion gear tooth count and multiplying that total by the internal transmission ratio.

A higher FDR will increase torque and acceleration (but reduce top speed). This is gearing down. A lower FDR will increase top speed (but reduce torque and acceleration). This is gearing up.

Gear Down – To install a smaller pinion gear or larger spur gear to increase the final drive ratio of your transmission, resulting in a higher gear ratio. Gearing down increases torque and acceleration but decreases top speed.

Gear Up – To install a larger pinion gear or smaller spur gear to reduce the final drive ratio of your transmission. Gearing up increases top speed but decreases torque and acceleration.

Gear Mesh – The clearance between two gears as they spin against each other. A gear mesh that is overly tight can cause excessive wear and drag, causing your motor to overheat and reducing performance. A gear mesh that is too loose can cause excessive gear tooth wear or stripping of the teeth on the gears, or other potential damage.

Idler Gear(s) – Gears mounted inside a transmission case between the input gear and the differential gear. The purpose of the idler gear is to change the rotational direction.

Input Gear (or Top Shaft Gear) – The gear attached to the input shaft on the transmission that directly meshes with the idler gear. The spur gear mounts to the same shaft as the input gear shaft on the outside of the transmission case.

Module – For countries that use the metric system, Module is the equivalent of pitch. It typically refers to the pitch diameter, in millimeters, divided by the number of teeth. The higher the number on the pitch, the finer the tooth profile is. The common module types are 1.0 module and 0.6 module.

Slipper Clutch – A device mounted to the top input shaft on off-road vehicles designed to reduce wear and tear on a vehicle's transmission gears and drivetrain over rough terrain. The slipper clutch is made up of some sort of slipper pad material, a slipper plate, spring and your spur gear. This is adjustable by changing the tension on the spring.

Transmission – A collection of meshing gears or pulleys designed to transfer and multiply the power from the motor or engine to the differential in order to drive the wheels. A transmission is designed to multiply the torque of a motor or engine.

Friday
Apr192013

Understanding RC gearing

This excellent video from Horizon Hobby (http://www.horizonhobby.com) clearly explains and demonstrates the must-know fundamentals of RC car gearing. 

Thursday
Mar212013

The racing line - cornering

This article has been reproduced from the RC Formula1 blog which reproduced the Launceston RC Racers website. Written by Scott Guyatt.

To go fast in R/C racing, there are four simple tasks:

1: Know the quickest way around the track.

2: Have the driving skills to get your car onto the racing line you’ve figured out in (1).

3: Setting up your car so that it’s capable of delivering fast times, and works in the way you need it to with your driving style.

4: Doing all of the above in traffic!

[This article] concentrates on the first task – knowing the quickest way around the track.

The Racing Line

Put simply, the racing line is the line your car will follow around the track that generates the fastest lap times.

In any given corner, following a line that gives the widest radius will help you carry the most speed through the corner. It’s a simple formula of traction vs centrifugal force.  Traction is roughly constant, so the tighter the corner, the slower the speed you can carry.  The objective is, in any given corner, to drive the “straightest” line possible – the widest arc, and carry the highest speed.

Read this Wikipedia article on finding the best racing line through a given corner.

Thursday
Mar212013

Motor turns & wind (Single, Dbl, Tri, Quad, Quint)

Motor turns refers to how many times the wire(s) are wrapped around the armature web. The more turns the motor has, the slower it will go. On the other hand, less turns the motor has the faster it is but the quicker it will drain your batteries.

Winding refers to how many wires are used to wrap around the armature web. A single wire wrapped around the web will increase the Torque curve through the whole RPM range of the motor. Double wires wind will also increase the torque curve but will allow for greater RPM's. Triple wires have large RPM ratings while having diluted torque. Quad and quint wires are built for extremely high RPM's.

Sunday
Mar172013

Common mistakes: Messing with the stock setup

Many people do two things when it comes to setup that they never should: (1) they experiment with every adjustment on their vehicle (often making multiple changes at once); and, (2) they change their setup to match a pro driver’s setup that they find online.

This may be fun, but it's not a good habit to get into if you want to get the best performance from your car.

To get the best from your car, simply use the stock setup. The truth is that most of us will notice changes outside of tires and springs. If you are going to see how a change impacts your lap times, you must make only one change at a time.

Second piece of best advice is to leave the pro setups to the pros. What works for one driver often won’t work for another and what works for a pro driver is almost never going to work for a hobby driver who has a totally different level of experience and skill. Often what happens when a hobby-level driver follows a pro’s setup, they end up with a vehicle that is too hard to drive and they go slower, not faster.