XRAY - Model racing cars

Ackerman - Original FK (FK04) & FK05

Author: TeamGP

Explanation

Ackerman controls the difference in steering arcs between the front inside and outside wheels. This is due to the fact that the inside wheel always has a tighter arc in any corner. The tighter the corner radius, the greater the difference in arc between the front wheels. But bear in mind that the turning arc is not the only factor in getting the best ackerman setting for steering. The amount of grip provided by the tires, in relation to the steering arc and speed of the car, create an amount of measurement called a "slip angle" for each wheel. For some tires you need a greater difference in slip angles between the inner and outer wheel and for some you need less. The size and geometry of the servo saver on Xray cars forces the inside wheel to increase its turning angle at a greater rate than the outside wheel, as the servo turns either way from top dead center. The result is a smaller turning radius for the inside wheel. The rate of the increase, called ackerman effect, can be changed by the angle of the steering rods connecting the servo saver to the steering blocks. The straighter the rods are in relation to each other, the more ackerman effect will be applied to the inside wheel. For example, if the wheels start with a toe of 0 and the servo moves to turn the outside wheel 5 degrees to the left, the inside wheel may be turned anywhere from 6 to 8 degrees to the left, depending on the angle of the rods.

Slip angles work differently on each wheel when the car is slowing down & pitching forward, than when the throttle is applied & the tires are pulling the car forward. The goal in tuning ackerman is to get the car to keep a consistent steering arc after going from off-power to on-power, while not allowing the front inside wheel to be turned too much, drag instead of roll, and therefore scrub speed in the corners.

The angle of the steering rods can be changed by using one of the two outer steering rod link mounting positions on the steering blocks. I call this tuning option "outer ackerman position". The forward most mounting position on the steering block (labeled #1 in the setup sheets) straightens the rods the most and provides the greatest ackerman effect. This normally is only used by drivers running rubber tires on low grip tracks. The rearward second mounting position on the steering blocks is the common starting point for all occasions. For drivers running foam tires on medium to high grip tracks, the optional ackerman extension plates provide a third more rearward mounting position for the least amount of ackerman effect. New steering blocks will be available soon from Xray with the third mounting position built-in.

For the FK04 only, you can also change the angle by mounting the inner steering rod link in the outer mounting positions on the servo saver. I call this option "inner ackerman position". This option has about half the effect as the outer ackerman position of the steering rods. Most drivers of the FK04 choose to keep the inner link mounts in the inner positions on the servo saver and then cut off the outer positions, in order to provide more clearance between the servo saver and the bulkheads when the steering is turned at full lock. Without this modification, if you hit a wall with the steering at full lock the servo saver may not have enough room to absorb the impact, resulting in a broken (or bent aluminum) steering block.

Drivers with a more aggressive throttle input will benefit from a greater ackerman effect as it keeps them from drifting wide on corner exit after they have hit the throttle hard and early in the corner. "Point and shoot" drivers will desire less ackerman effect in order to keep them from over steering.

I personally have an aggressive throttle finger and prefer to have the static front toe-out set to 0. Setting static front toe to a positive amount will have an effect on the inside wheels turning rate as well. However, it is mainly used to increase turn-in responsiveness and the effect on the rate of change will be more linear and not exponential as it is with changing the rod angle.

Testing Completed

I have tested all three outer steering rod positions using foams on medium/high grip carpet (FK04 & FK05) as well as using rubbers on low grip asphalt (FK05 only). I never tested using the servo saver outer mounting positions as I had cut them off. Although most of this testing was completed in the far past, I'll do my best to provide what I remember.

For the FK04 with foams on carpet, I actually found that using outer ackerman position #1 was needed if both sides of the saddle pack were battery were in the rearward slots and I was not getting enough traction from the front end on-power. With the heavily biased rear end of the FK04, on-power steering was hard to come by, even in high grip situations. At first I ran a combination of full ackerman position #1, stiffer (3lb less than front) and more upright (2nd hole in) rear springs, and a .5mm higher rear ride height, to try to get more weight onto the front inside wheel for better on-power steering. But after repositioning the electronics more forward, and a lot of trial and error with many other suspension tuning options, I was able to use outer steering rod position #2 and still get enough on-power steering with a consistent steering arc during throttle transitions. My last full setup can be found in the Xray on-line setup sheet section here:

http://www.teamxray.com/xforum/xform/in ... tup=t1fk05

For the FK05 with foams on carpet, I prefer to use outer ackerman position #2, rather than the commonly used position #3 given by the ackerman extension plates. This may be due to the fact that I have an aggressive throttle finger, which has been confirmed by a few of our local aces having difficulty driving my car on-power. I tested with position #3 on the extension plates. However, this required me to either increase the steering dual rate on my transmitter or run a positive front toe-out setting in order to get enough corner exit steering. But both of these ended up giving me too much over steer entering tight corners at high speed. Outer ackerman position #2 gave a little too much on-power steering, but this was easily cured without any other adverse effects by increasing the front droop by .5mm. When testing with position #1 (and after dialing down the dual rate), I could hear the inside front wheel dragging the carpet on corner exit and I would have to dial down the dual rate, which gave me too little corner entry steering. My current full setup can be found in the Xray on-line setup sheet section here:

http://www.teamxray.com/xforum/xform/in ... tup=t1fk05

For the FK05 with rubbers (CS27's up front and 22's in the rear) on low grip asphalt, I prefer to use outer ackerman position #1 when running mod motors for more corner exit steering. But position #2 is adequate when running stock or locked timing 19 turn motors. My current full setup can be found in the Xray on-line setup sheet section here:

http://www.teamxray.com/xforum/xform/in ... tup=t1fk05

Conclusion

If the car steers well off-power but pushes on-power, then use more forward positions to straighten the angle of the steering rods. If the car is good on-power and pushes off-power, or if you can hear the front inside wheel chattering/squealing mid-corner, then use more rearward positions to increase the angle of the steering rods.

Gearing - All Models

Author: djnutz

Explanation

Gearing is one of toughest things to nail down. There are a lot of different types of RC cars, but they all have one thing in common and that is gearing. Your first time racing usually goes like this: You ask the person next to you what spur and pinion gears they are using; you try the same setup and then find you are more than a lap slower. Then you go back to your pit and try going up a tooth on your pinion. Now your car is faster, but you can’t finish the run because your pack went dead, or even worse, you cooked the motor. Finally, you get discouraged because you can’t seem to find the perfect balance between speed and runtime.

The problem is that you are asking for the wrong information. When you go to any track for the first time, you should ask around about each driver's rollout and not their gearing. If they can't or won't tell you, move on to the next person and keep asking. Once you find a driver in the same class you are running that tells you his rollout, you will then be able to match your cars rollout to theirs as closely as possible for a good base gearing setup to start with. Once you have done this, the only factors that will affect your lap times, outside of chassis tuning, are driver skill, power output of the motor and obviously changing the spur or pinion gears to a different size.

What is rollout? Rollout is the distance the car will travel in one revolution of the motor shaft. Pinion and spur gears are used to generate the rollout desired. If you take a shaft car and a belt car with the same exact motor and rollout, they will have the same theoretical top speed. The higher the rollout number is, the slower you will be off the line (less acceleration) and the faster the top speed will be. The lower the rollout value, the quicker you will be off the line, but with a lower top speed. Now, let’s get down to the business of how to calculate rollout and setup your gearing accordingly. I am using numbers from my car, an original T1 with modifications, for all of the following examples. What can I say, I love it and it’s still in one piece!

NOTE: Keep in mind that all of the numbered values in this example will not necessarily yield the same results for your model of car!

Calculating Rollout

1. Determine the Drive Train Ratio (DTR) - The ratio of all the internal gears from the transmission, including differentials and pulleys is known as the drive train ratio. The drive train ratio is usually different for each model of car. Your owner’s manual should provide this information, but keep in mind that some manufacturers use the words "transmission reduction" or "internal reduction" to indicate the DTR. The DTR in most cases cannot be changed, unless you are able to change the number of teeth on the pulleys and/or gears. My original T1 has the Xray low ratio pulley set which provides a DTR of 1.77.

2. Determine the Primary Drive Ratio (PDR) - The ratio between the pinion and spur gear is known as the primary drive ratio. This number is commonly rounded up to the nearest thousandth after the decimal point.

Spur / Pinion = PDR

My cars PDR: 93 / 24 = 3.875

3. Determine the Final Drive Ratio (FDR) - The ratio between the DTR and the PDR is known as the final drive ratio. This number is commonly rounded up to the nearest thousandth after the decimal point.

PDR x DTR = FDR

My cars FDR: 3.875 x 1.77 = 6.859

4. Determine the Rollout - Rollout is not affected by the motor, batteries, or electric components you are using. Rollout simply defines how all of the gears, belts/shafts and tires work together to make the car accelerate and reach top speed. Rollout is affected by your tires diameter, but don’t ever let anyone tell you that rollout only matters if you run foam tires. Rollout is calculated using tire diameter and therefore the diameter of both foam and rubber tires make a difference since both wear down. However, the diameter is more important if you run foam tires since they can be used anywhere from 64mm to 55mm. And as they wear and get smaller, your rollout value will change a lot more. Rubber tires do not wear down near as fast or as much so the change will be much less. The circumference is commonly rounded up to the nearest hundredth after the decimal point. The rollout is commonly rounded up to the nearest thousandth after the decimal point for American standard and to the nearest tenth after the decimal point for metric. My car has Take Off CS32 rubber tires with a diameter of 2.4375 inches (62 millimeters, although it’s common to find that other drivers use 63mm for a rubber tire diameter).

Tire Diameter X 3.14 (value of PI) = Tire Circumference

Tire Circumference / FDR = Rollout

My cars tire circumference: 2.4375 x 3.14 = 7.65 inches (or 194.68 millimeters)

My cars standard rollout: 7.65 / 6.859 = 1.115
* The car travels 1.115 inches for each revolution of the motor shaft
Or metric rollout: 194.68 / 6.859 = 28.4
* The car travels 28.4 millimeters for each revolution of the motor shaft

5. Determine the Top Speed - Theoretical top speed can be obtained by combining the maximum dyno’d RPM with the rollout number. However, this does not take into account the forces that will slow your car down, including aerodynamics, drive train efficiency and motor power. Most brand new motors have their maximum RPM on a label attached to the motor can. You can also have your motor dyno’d to find out what the maximum RPM is.

( ( max RPM / FDR ) * Tire Diameter ) / 336.135 = Estimated Top Speed in Miles Per Hour (MPH)

NOTE: The number 336.135 is used to convert the results to MPH.

Completed Testing

Using the same battery pack for all testing, I ran my car with three different gear combinations, while maintaining as close a ratio as possible. For each combination I made three runs to get an average runtime and top speed. The only discernable difference was that the change in spur changed the motor height in the chassis. The taller spur placed the motor lower in the chassis and provided faster cornering speeds.

Conclusion

Once you get the hang of the equations you will notice that some of the gear combinations will yield similar numbers. For example, some of my current gearing combinations below have really close rollout figures.

90 spur and 23 pinion results in a rollout of 1.106
93 spur and 24 pinion results in a rollout of 1.116
99 spur and 26 pinion results in a rollout of 1.136

Changing either the pinion or the spur to maintain a consistent ratio will not affect your overall speed or runtime. Increasing the number of teeth on the pinion by one is pretty close to increasing the number of teeth on the spur by 3 or 4. This knowledge is very useful with all of the Xray chassis previous to the FK05. This is due to the fact that the size of the spur and pinion dictate the height of the motor in the chassis. The lower the motor, the lower the center of gravity in the rear of the car.

I have a theory that applying the same amount of torque over a larger area should make for a more efficient use of motor torque. This theory would state that using a 93t spur and 26t pinion (1.208 rollout) would be better than using a 90t spur and 25t pinion (1.201 rollout). This is due to the fact that there is more surface contact between the gears where they are meshed, which will spread out your motor's applied torque across more of the teeth surface area.

There really isn’t anyone who can tell you the best gearing for any specific track since each driver and car setup differs. The best advice I can give is to ask the drivers that are turning the quickest laps what their rollout is. Then match your rollout to theirs and go for it.

If you find that your motor is too hot after the first ten or so laps first check that there are no parts binding in the drive train. You can do this by taking the pinion off the motor shaft and giving the spur gear a spin. If they don't free roll for a few seconds or it seems a little gritty then it is time for a good bearing, axle coupling and/or diff cleaning. All of these can trap dust and dirt or become damaged from a crash. I would also give the motor a good once over cleaning. If neither of these helps, drop one or two teeth on your pinion gear, and try to find the best driving line around the track. Here is an awesome site that deals with motor maintenance. The rule of thumb is CLEAN IS FAST.

http://www.motortuningsecrets.com

If your motor is less than 140 degrees Fahrenheit after at least a four minute run, you could try to go up one tooth on the pinion.

Here are two ways to get quick FDR and rollout numbers.

1. Online Gearing Website

http://www.gearchart.com

2. Gearing Spread Sheet

To make things easier, and since I have a full pinion set from 18-35t and three different spur sizes, I created a Microsoft Excel spreadsheet to perform the calculations. Once I enter the pinion and spur gear values, Excel does the rest. Row one is my header row with the column labels in this order:

Spur(column A), Pinion(column B), Tire Diameter(column C), Final Drive Ratio (column D), Rollout (column E), Estimated Top Speed (column F)

Here are the equations that you can cut and paste directly to your own Excel spreadsheet if you like. I have listed the equation and then what each value stands for.

* Final drive ratio equation for all rows in column D and starting on row 2:

=A2/B2*1.77

Note: 1.77 is the internal reduction (DTR) of my cars transmission. Replace this number with your own models DTR.

* Rollout equation for all rows in column E and starting on row 2:

=(C2*3.14)/D2

Note: The first part of the equation determines the tire circumference

* Estimated Top Speed equation for all rows in column F and starting on row 2:

=((21529/D2)*C2)/336.135

Note: 21529 is an example of the maximum RPM for a good stock motor. Replace this number with your own motors maximum RPM.

Good luck at your next race!

Gearing FAQ's

* What range of gears can be used on the T1FK05
http://www.teamxray.com/xforum/viewtopi ... 1662#21662

* Aren't the XRay spur gears too soft?
http://www.teamxray.com/xforum/viewtopi ... 1660#21660

* How do I prevent the spur gear on my T1FK'05 from breaking?
http://www.teamxray.com/xforum/viewtopi ... 1661#21661

Pre-race Alignment & Setup Tips – All models

Author: TeamGP

Explanation

Good setup books like "XXX Main" can leave out important definitions of terms used in RC Touring Car (TC) tuning and understanding of specific and overall chassis dynamics. Therefore I'd like to help all of the new Xray owners by providing a good starting point for tips, tricks, methods and recommended tools concerning HOW TO measure and adjust the alignment of any Xray TC model. I have purposely avoided answering the questions concerning WHY you should adjust your setup. That type of information can already be found in the Hudy Setup book and the existing threads on this forum. This topic focuses on a very broad subject with ideas that may evolve through time, technological innovation and new model releases.

I have described my method of checking & setting a cars setup in the following section and decided to use the term "full alignment" to describe this overall set of ordered tasks. It makes me feel a lot better realizing that I know just as much as the, never immediately available or helpful, mechanics that service my full scale vehicles. Please feel free to PM me with anything you see that could be improved or is simply wrong.

Procedures

NOTE: All measurements are taken using a perfectly flat Hudy setup board and setup station tools.

1) Mount everything that will be used for a typical run on the track (battery, motor, transponder, etc.), except the body, clips and tires.

2) Check the "chassis tweak"

First, place the chassis on two downstop (droop) gauge blocks of equal height. Center each one directly beneath the front and rear axles. Using your thumb and a finger from one hand, press down on the outside tips of the shock tower furthest away from you and then use your other hand to press down and release EACH side (separately) of the shock tower facing you and see if the chassis rocks in a cater-corner fashion, or if there is a sliver of light that appears and goes away between the edge of the chassis and the block on the side that your pushing down and releasing. If so, then "barely" unscrew the chassis, top deck, shock towers & front bumper from the bulkheads, lightly twist the chassis back flat and systematically tighten the screws back, being careful not to strip them. Check the chassis tweak and adjust it if necessary a few times while tightening the screws to make sure it stays flat. Use this order when tightening the screws: 1)chassis bottom 2)top deck 3)shock towers 4)front bumper.

3) Mount the tires

If you are using foam tires, true them first and make sure the front and rear sets of two are equal in diameter by using a digital caliper. Make sure to pay attention to actual trued diameters as they will significantly affect both ride height and overall handling. Regardless of tire type, check the rims to see if they are out of round and shaped like an oval. If they are, make sure they are not cracked and then carefully bend them back into a circular shape.

NOTE: I have found that most people don't pay enough attention to their tires. While in any form of scale racing you'll find that the engineers & mechanics confirm their drivers’ analysis of how the setup is working by analyzing tire wear on EACH tire. And they hardly ever go through the pains of setup/adjustment and then throw on a pair of used tires that they haven't checked to make sure they are all the same size and worn evenly across. Too many people at our local tracks have given up on their cars handling problems and been willing to even sell their car. Then after getting permission from them, I check their tires and notice that there are different sizes on all four corners, or at least one or more of them is worn too much on the inside or outside edge.

NOTE: The car should now be in an almost ready to operate state with just the alignment adjustments and mounting of the body to be completed. It is ok to use a discharged battery, of similar size and weight, for correct weight distribution during the alignment process.

4) Preliminary camber adjustment

If you have replaced anything that affects the camber on the front or rear, eyeball each tire and make camber and front toe adjustments in order to get the left and right sides at each end to look similar. Using a simple tool like the RPM gauge is recommended, but I use my own eyesight. This is only a preliminary step and the final camber will be fine tuned later on the setup station. If you have the time to mount the setup blocks, it is preferred that you set the preliminary camber using the setup station. However, during a race day you seldom have time to do this after making a significant change.

5) Set the ride height

If the weight distribution has been changed in any way since the last alignment, always place the adjustable shock collars at the same distance from the thread "stop", towards the top of the shock, while trying to get the ride height set. Later in these procedures each end of the car will be balanced to compensate for their respective weight distribution and slight variations in left/right spring rate. If the cars weight is not balanced between right and left, or if the foam tires on one side are a little smaller in diameter than the other side, then it is acceptable if the ride height on the lighter/taller side is .1 to .2 mm higher than the left. For example, if you want to run a 4mm ride height then make sure the heavier/shorter side is at least 4.0mm and the lighter/taller side will usually end up around 4.1 to 4.2mm during this step.

NOTE: It is highly recommend that you balance right and left weight. But it is not necessary to true your foam tires before every run and throw away money if the tires are wearing evenly. Therefore always use this method to check and set the ride height when needed (like after a crash or spring rate change). It is also recommended that you rotate your foam tires left to right every 1 to 2 runs.

6) Mount a set of aluminum setup wheels (Integy, HPI, 3Racing, Take Off, Losi) or any four wheels of the same exact diameter to ensure identical wheel diameters on all four corners for the following steps.

7) Set the downstop (droop) screws

Check and set your downstops during each full alignment in order to maintain actual "droop" as measured by the up travel of the chassis at each end of the car. This measurement is also referred to as the down travel of the arms. For each end of the car do the following:

* Preset your downstops by measuring the up travel of the chassis from "at rest" to when the right rear or left front wheel lifts off the ground. Place the ride height gauge on your left and watch the wheel that is on your right, while each end of the car is facing you. Once you have set the right amount of chassis up travel on the tire on your right, move the gauge and adjust the tire on your left so that both tires lift off the ground at the same time. This setting is preliminary but important and it will be fine tuned next.
* Remove the wheels, unscrew the lower shock ball ends and place the chassis on the downstop blocks. Remember that the chassis tweak has already been eliminated and the downstops on the right rear and left front arms are already at the desired droop setting needed for your desired amount of front/rear weight transfer. Use the downstop gauge to measure the right rear and left front arms downstop setting. Write down the front and rear downstop setting & ride height as they correspond to one another and changing either will change the amount of chassis up travel. Adjust the left rear downstop to match the right and the right front downstop to match the left. It is recommended to take measurements under the lowest point of the front and rear hubs (including any set screws).

8 ) Mount the set of equal diameter wheels from step 6

9) Eliminate "spring tweak" WITHOUT a tweak station the old fashioned way

Place the car on the setup board, eyeball the front wheels and manually center the steering. For each end of the car do the following:

* With the setup board flush with the lip of your workbench, let the tip of the chassis hang over the end of the setup board
* Lightly press down and release the center of each shock tower, starting with the one closest to you, to settle the suspension
* Place the tip of your trusty hobby knife directly in front of the chassis balancing hole on the end of the car in front of you and lift the chassis up until one or both wheels lift off the ground
* If one side lifts before the other, then the adjustable spring collars on the shocks at the end of the car furthest from you need to be adjusted to compensate for the weight distribution at that end. For example, if the rear end is facing you and the right rear wheel lifts before the left, then the front left shock collar is too high in relation to the front right and the chassis is dipping down to the left up front. Fix it by twisting the left front shock collar clockwise (raises ride height at that corner) one or more turns AND ALSO twist the right front shock collar counter-clockwise (lowers ride height at that corner) the same amount of turns in order to keep the ride height at that end of the car the same.

Recheck and repeat these steps until both setup wheels lift off the board at the same time at each end of the car.

10) Set the camber and toe

Replace the setup wheels with the setup systems camber/caster/toe gauges. Check and adjust the camber first. In my experience, changing the camber even a half degree will change the toe at that end of the car significantly. Check the toe setting and adjust the steering rods for front toe or change the shims for rear toe accordingly. Re-check and adjust the camber after changing the toe to make sure it is set correctly.

11) If any of the camber settings needed to be changed more than a half degree, or if the shock collars had to be turned more than half a turn, then repeat steps 8 and 9 one more time since the camber angles being off could have made the setup wheels give an inaccurate spring tweak reading the first time. I look at this as a case of "the chicken before the egg", but repeating these steps should be accurate enough.

Conclusion

Though it sounds like a lot, you should be able to complete a full alignment like this in about ten to fifteen minutes. I highly recommend doing so after a hard crash and before every main if you’re not already battling with setup, motor, battery or workbench neighbor issues.

2mm chassis - a must have for rubber carpet racing

Tech Tip by Martin Hudy

The carpet season has already started and I have done more than eight races. On my first carpet race this season in Las Vegas, I had a problem finding a working setup which motivated me to spend countless amount of time on carpet track to practice and work on the car set-up. Later on we had a race with the same tires (Take Off CS27) as used in Vegas and after fine tuning I have found a very good setup which works perfectly with these tires as well with any other rubber tires. I already tried this setup on five different carpets including a brand new, no-grip carpet. My car was perfect the entire time and I have won at almost all races. If you want to follow my setup sheet, here are couple of small details on which you should concentrate.

The first thing to start with is the . We were positively surprised with the excellent performance of the car with 2mm chassis on the carpet with rubber tires and I and the whole European team have not used anything else since. The 2mm chassis will make the car very soft and this will increase the grip. To make the car even softer and have sufficient amount of grip on all tracks I changed from the adjustable top deck to the , which I then modified to make it even softer without the front alu stands. Check out the photo where you can see how I have modified the top deck. You can do it easily, just take a Dremel and make a groove in the middle of the chassis. (For your safety please make sure that you have protective gloves and safety glasses all the time when you want to modify any parts or the graphite parts.)




At some tracks I still faced a problem that my car used to stop in some corners. I solved this problem by using [url=http://www.teamxray.com/teamxray/products/proddesc.php?prod_id=480&kategoria=0[/url]blue springs (308395)[/url] on the front shocks. These springs are quite stiff and you will have no longer a problem with stopping in the corners. I use in the rear to achieve the required grip but at the same time to keep sufficient cornering speed. If the grip is very low you can try in the rear which will give even more grip but this will decrease steering.
To achieve a sufficient grip it is very important to have 3° rear toe-in. The is great for all racing conditions on asphalt, which is the only top deck I use outdoors, but for indoor carpet racing with rubber tires the standard top deck with the modification I made makes the car to handle best. This modified top deck is also very good on very bumpy tracks because the car will absorb bumps better. On a brand new carpet which had no grip at all I even removed the two front screws from the top deck which mount the top deck to the rear bulkhead. Once you remove these screws the car will have more rear grip and you do not need to be afraid of losing steering because these screws have no relation to the steering.

Remember that body choice is very important too. In very low grip conditions you should use the Stratus1. In case you need to have more steering you can try the Stratus3. The Mazda6 is perfect in high-grip conditions because it gives you more steering but less grip.


For further details check out and follow . In case you drive with rubber tires on carpet, I strongly suggest that you use my setup sheet as a starting point and you can tweak and fine-tune things from there.