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  1. #1
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    Gear ratio program and speed calculator. Free and easy!

    WARNING: This program may cause you to do less bashing and more speed runs! This is a real good program i found and have been using for a long time now. All you have to do is enter your info such as tranny (2.72 if its the magnum), tire diameter in mm, spur tooth count, pinion tooth count and scroll down and pick whether you want km/h mph, gear or roll out ratio and it will make a professional chart for you for free. You can also choose where you want to plot your settings on the chart so you can get results for ranges that are only higher or only lower, or just keep the default setting of in the middle and it will give you some of both. You can also name the chart to differentiate between them if making multiple charts. Don't worry about the drop down menu of choosing the brand or type of car you have cuz no traxxas on there, but you dont need to choose anything here for it to work. REMEMBER that the results that are given to you are for reference only and would only be accurate in a perfect world, not ours. But is a great tool for helping achieve results for speed runs and to give an idea of speeds when choosing your gearing.

    To get your motor rpm for brushless just multiply you battery pack volts x kv rating. Example - 8.4 volt x 3500kv = 29,400rpm.
    Do not enter your motors maximum rated rpm unless you have a battery pack that can provide the power to achieve this.

    Tire diameter must be in millimeters only.

    The stampede magnum tranny gear ratio is 2.72

    Remember that when you enter spur and pinion counts, you will need to refer to your truck's manual or to a gearing chart by traxxas for your transmission to make sure that these combinations will fit in your tranny.

    Do not buy gearing based on results of this chart until you know that it will fit in the tranny you have.

    Hope this helps those of you planning on doing speed runs or simply just as a reference for gearing.

    Good luck and have fun!

    http://www.RCRacing.com/Gear_Ratio_Program_1100.cfm
    Last edited by BaldyDaniels; 05-20-2011 at 07:25 PM.
    Never trust an "Atom", they make up everything.

  2. #2
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    Calculators, converters and many other services for your rc vehicle!

    I came across this site that has a calculator for pretty much every aspect of rc vehicles. Its an amazing thing to have on hand, and they have traxxas specs in drop down menus of the speed calculator as well as most brushless motor brands and their kv ratings and tons of tire brands and their respective diameters. It even has an input for the accounting of tire ballooning if you have an idea of the amount of the diameter increase! Just pick the brand names and the calculator does the rest!
    Top speed estimator
    Speed vs amps calc.
    Scale speed calc.
    Rollout ratio calc.
    LED Wiring and voltage calc.
    Charging calc.
    Unit conversions
    Thats only about half of the services it has!
    Also in the tips box, if its not showing already, just click on show next tip until you get to the one that allows you to download a zip fil to be able to use all the calculators, converters and other services without an internet connection.
    Check it out!

    http://scriptasylum.com/rc_speed/index.html
    Last edited by BaldyDaniels; 06-07-2011 at 10:05 AM.
    Never trust an "Atom", they make up everything.

  3. #3
    RC Turnbuckle Jr. DiggerPede's Avatar
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    Dude, Thats awesome! ;-)
    Weak Revenge
    Strong Forgive
    Intelligent Ignore

  4. #4
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    does this sound right?
    I entered my stampede for the mph
    It came up with a 7700kv motor and 3s lipo and stock gearing(19pinion 86spur) it should do around 95mph.

  5. #5
    RC Racer
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    Amazing, Thanks guys! This is awsome. Will deff help me work out gearing for my next speed run.
    Flying is easy, landing however....

  6. #6
    RC Turnbuckle Jr. TAT2's Avatar
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    Just remember that these calculators are really estimators. The numbers they spit out, particularly with regard to top speed, are a bit exaggerated since they don't take into consideration many factors which will directly affect your top speed. They are useful tools, but just because it says you're truck will go X mph... don't assume that it will actually reach those speeds just because one of these says it should. They are fun to play with though, and they can be useful for comparing the effects that different gearing will have on your speeds.
    Last edited by TAT2; 06-07-2011 at 01:28 PM.
    99%er

  7. #7
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    Thanks for the disclaimer TAT2. I realize that but I'm sure there are people that think these are the realistic speeds. The gearing I have in my pede now the calculator says that is going to do 65MPH, I know for a fact that it isn't going to do 65MPH. But its nice to dream! LOL

    Another item I guess to remember(Correct me if I'm wrong please), is the condition of your battery pack. Just because your pack says 8.4V doesn't exactly mean its pushing 8.4V. So doing your calculations based on a 8.4V pack that is only pumping 7.8(just a random number) your motor RPM's are going to be off, so the whole calculation is going to be off...
    Flying is easy, landing however....

  8. #8
    RC Turnbuckle Jr. TAT2's Avatar
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    Quote Originally Posted by Arsenios View Post
    ...I'm sure there are people that think these are the realistic speeds.
    Hence my "disclaimer." I've seen far to many people get angry, and wonder what is wrong with their setup when their vehicle doesn't reach the theoretical top speed that one of these says it should.

    Quote Originally Posted by Arsenios
    Another item I guess to remember(Correct me if I'm wrong please), is the condition of your battery pack. Just because your pack says 8.4V doesn't exactly mean its pushing 8.4V. So doing your calculations based on a 8.4V pack that is only pumping 7.8(just a random number) your motor RPM's are going to be off, so the whole calculation is going to be off...
    That would be another factor that would directly influence the speed your vehicle is able to reach, which isn't taken into account by these.
    Last edited by TAT2; 06-07-2011 at 01:55 PM.

  9. #9
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    Quote Originally Posted by jakeson81798 View Post
    does this sound right?
    I entered my stampede for the mph
    It came up with a 7700kv motor and 3s lipo and stock gearing(19pinion 86spur) it should do around 95mph.
    You have to remember that your motor has an maximum rpm limit. If it didnt that would mean your motor would hit just over 85000 rpms to get to that speed. Kv x volts = rpm, but only to the limit of your motor.
    Are you having any heat issues with your setup. Maybe its just me, but your gearing seems a little high for that much kv.
    Never trust an "Atom", they make up everything.

  10. #10
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    Quote Originally Posted by BaldyDaniels View Post
    . REMEMBER that the results that are given to you are for reference only and would only be accurate in a perfect world, not ours. But is a great tool for helping achieve results for speed runs and to give an idea of speeds when choosing your gearing.

    To get your motor rpm for brushless just multiply you battery pack volts x kv rating. Example - 8.4 volt x 3500kv = 29,400rpm.
    Do not enter your motors maximum rated rpm unless you have a battery pack that can provide the power to achieve this.

    Tire diameter must be in millimeters only.

    The stampede magnum tranny gear ratio is 2.72

    Remember that when you enter spur and pinion counts, you will need to refer to your truck's manual or to a gearing chart by traxxas for your transmission to make sure that these combinations will fit in your tranny.

    Do not buy gearing based on results of this chart until you know that it will fit in the tranny you have.

    Hope this helps those of you planning on doing speed runs or simply just as a reference for gearing.

    Good luck and have fun!

    http://www.RCRacing.com/Gear_Ratio_Program_1100.cfm
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    THIS APPLIES TO ALL SPEED CALCULATORS, THAT IS WHY THEY ARE CALLED SPEED ESTIMATORS!!

    Thankx Tat2 for reminding everyone that these speed estimators are not to be taken as guaranteed results.
    Never trust an "Atom", they make up everything.

  11. #11
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    Here's one that I use and I find it accurate.
    It also takes into consideration Voltages, vehicle weight, and various other criteria.
    The best i've found yet.....http://www.dhrc.rchomepage.com/RolloutCalc.htm

  12. #12
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    Quote Originally Posted by damselfly View Post
    Here's one that I use and I find it accurate.
    It also takes into consideration Voltages, vehicle weight, and various other criteria.
    The best i've found yet.....http://www.dhrc.rchomepage.com/RolloutCalc.htm
    Thanks for the input, always good to have options and more good info on the forum.
    The link you provided may be a little bit advanced for beginners, but has some excellent points that a lot of newcomers to the hobby should read and understand, so i will post it here:

    - To easier compare setups, define two Restore buttons, use 'undo' and 'redo' buttons or launch 2 versions of the calculator page
    - Things to be taken into consideration when assessing the calculator results:

    Rollout: is just an interesting number that you may or may not find a useful indicator for your setup. For a small RC electric vehicle, some might say that a rollout of around 1 inch per motor rev is thought to be a good starting point for a setup BUT this doesn't mean you should aim for this religiously. It depends greatly on your desired application and the performance abilities of the setup's components (cells, motor and ESC etc.). There is no allowance in the calculations for actual real work performance with regard to torque and heat issues. In other words, a setup that looks good on paper in theory may over heat and destroy itself in the real world. You need to apply some experience and be prepared to carefully experiment what works in your application (on road, off road, big or small), balancing performance for acceleration vs. top speed vs. component life span etc.

    Just because the numbers look good in the calc doesn't mean your motor and cells can deliver the required torque and cope with the associated heat demands of your setup configuration. We are not modeling for friction, air drag, tyre swell and such as like can impact upon your top speed. The calculator should really be thought of as an estimator at best (think 'ball park').

    How accurate is the motor kv (rpm/v) rating, some motor winds seem to vary.
    Operational battery voltage under load, so try out the middle three radio buttons (pack voltage) for a better guide range. The actual efficiency of the motor and other drag factors such as gear mesh drag.

    - Brushed motors are in the 60-70% efficiency range and brushless may achieve 75-90% efficiency.

    - Trans ratio (short for transmission ratio) is also known as the car's internal ratio which is built into the differencial gears. The internal ratio is multiplied by the gear ratio (Spur/pinion gear) to generate the final gear ratio, the total gear ratio used between the motor and the wheels.

    - When using the pack voltage radio button Full to Flat you will notice that Amps and Watts are also recalculated to show a lower Amp draw at higher voltages. Note the effect is exaggerated as the Wheel RPM also increases at higher voltages and would use more Amps to over come drag, something not modelled in this simple version.

    - Take into account the at full speed 100% throttle your setup may have some wheel slip, tire swell (to a larger diameter), voltage sage, motor rpm limitations, increased vibration, increased drive train friction, aerodynamic drag... etc.

    - Some text fields can be typed into and auto update when clicked, tab'd away or just press return.
    - Edit the average Amp consumption rate to estimate maximum battery pack runtime.
    - Alternatively, if you know your setup's run time then enter the number on mins and calculate back the average Amp draw (if 100% capacity could be used).
    - Note that you can shift the pack voltage with the radio buttons, just a guide to Amp draw ranges, not for true runtime calculations as there is no way to correspond a pack voltage to remaining capacity under unknown loads.
    - 'Efficiency/throttle' means you can use the drop % as a throttle if you wish but remember to drop at least 10 to 20% for real world losses. 90% is about the best zero load performance your going to ever see. Note that ESC's throttle % are not normally as linear.
    Given that the Kv of your motor may vary +/-10% from manufactures spec, the true condition of your batteries under load, your ESC motor timing is set aggressively etc. etc. etc. all can significantly impact real life numbers. You get the picture though right ... ball park estimates.
    Never trust an "Atom", they make up everything.

  13. #13
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    ^^^^^^^^^^^^^^^^^^^^^^
    Last edited by BaldyDaniels; 06-08-2011 at 01:06 AM. Reason: Double post
    Never trust an "Atom", they make up everything.

  14. #14
    RC Turnbuckle Jr. BaldyDaniels's Avatar
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    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    Last edited by BaldyDaniels; 06-08-2011 at 01:05 AM.
    Never trust an "Atom", they make up everything.

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