Quote:
Originally Posted by wongy008
cheers for doing that. i tried using the gear chart but its far too complex for me to follow
what is the difference between the 23t im running and 19t. how much difference in acceleration and top speed
currently its fast enough to keep me entertained but any slower ill be bored 
will hitting sweet spot just increase longtivity of motor ?? |
Wongy,
Happy to help.. The 'sweet spot' will both increase the longevity of the motor and ensure that you get maximum performance for the longest amount of running time (since you are not likely to overheat the motor).
I will admit that I have overgeared on purpose even after doing the gearing math. The first motor I used was a Novak 17.5 so I could qualify to race in the "Stock" class at my local track.. Each race is only 5min long, so I overgeared a bit to get a little more top speed.. So long as I kept my runs at 5min, my motor did not heat up very much.. 8+ minutes and it would get pretty warm.. So sometimes it is OK to push your motor a bit so long as you watch it closely.. But knowing which pinion is best to start with saves a lot of guesswork.
Your 23T pinion gives you a theoretical top speed of 58MPH, which is pretty darn fast. I have always wondered what the acutal speeds turn out to be once the motor is under load.. I currently do not know a way to measure accelleration using a math formula.. You get instant torque with electric motors, so your top speed can usually be reached in a second or two if you are running on pavement.
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I made a quick walkthrough for anyone that wanted to use gearchart.com. This should make it alot easier:
This will help you target the -sweet spot- for gearing so you can get the most out of your motor without overheating...
NOTE: The most important thing to make this work is that you have a good idea what your motor "RPM" is and also what the target "Gear Ratio" is for your motor. High end companies like Novak provide this information (as do other brushless motor manufacturers). I found it harder to find this info for brushed motors...
Lets get started with a "real world" example for my Durga when I ran a Novak 17.5 brushless for Novice and Stock racing:
1. First lets go to www.gearchart.com and click "Gearchart Creator" on the upper left side of the screen
2. The "Select an RC Car" pulldown menu does not have the Durga, DB01, etc.. So select "Pan Car (10/12th scale)" and we will fill in the blanks
3. The "Transmission Ratio" is 2.055.. It is the same for "ALL" DB-01 cars.
4. Next enter your "Spur" and "Pinion" sizes.. I switched to an 81T Spur gear and 31T Pinion gear when I installed my 17.5 Novak since it was better suited for the slower motor
5. The "Plot Spur/Pinion" option with the "Middle" setting is fine.
6. Now click the "Gear Ratio" button.. The chart it builds will have key information to see if you will -burn up the track- (yeah) or -burn up your motor- (bummer).
7. In my case I needed to know what Novak recommended as the Gear Ratio for my motor.. I went onto Novak's website and pulled up their gearing recommendations: http://www.teamnovak.com/tech_info/b...r_gearing.html
8. It showed that a 4WD (my Durga) should target a "6" (or 6.00) gear ratio with their 17.5 motor.. My Spur and Pinion combo put me at "5.37" so I was a little overgeared for their spec.. I wanted to push my motor a little bit for more speed, so this seemed fairly safe for a shorter 5min runs.. If I wanted to be right on spec with the Novak chart, then I would gear down to a 28T Pinion since that would be "5.94" which is super close to 6.00..
Ok, so this told me that I'm not likely to turn my motor into a -molten ball of fire- by pushing it too hard.. Now I wanted to get a ballpark on how fast my car might go..
9. The next part was "Rollout".. Rollout tells you how far your car will travel per motor revolution.. My Tire Diameter (measurement from one side of the tire to the other) was 85mm. It will likely be the same for you and most tires you will run..
10. Keep the "Increment" setting at "1mm" and click the "Rollout" button
11. I got "49.73", yipee!! What the heck does that mean.. Well, its telling me my Durga has the potential to travel 49.73mm every time the motor completes one revolution. That's about 1.9 inches.. This isn't too exciting yet, but it will help us get our MPH in the end..
12. The last part was the "Motor RPM".. This is important and requires as little guessing as possible to get an accurate number.. I consulted the "Novak Brushless Motor Spec Chart" to figure this out: http://www.teamnovak.com/products/br...spec_chart.htm
13. The chart says that I am running 2200Kv (or RPM per volt) for my 17.5 motor. I'm using a 7.4v lipo, so I multiplied 2200 * 7.4 to get "16280" which is my max RPM.
14. I entered 16280 as my RPM and clicked "MPH".. The chart showed I had the potential to go 30.2 MPH.. Not bad for a 17.5 Brushless running with pretty safe gearing for short racing runs..
Hope this helps.