Spektrum Telemetry - "ROLL OUT" Issue
08-08-2006, 09:25 PM
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Spektrum Telemetry - "ROLL OUT" Issue
I tested out the telemetry unit in my Jammin CRT today. The speed in MPH was way off.
QUESTION: When figuring out the roll out, do you use the car's INTERNAL gear ratio (3.3) or the FINAL ratio (14.5). I have the sensor mounted to pick up off the spur gear. Why would I use the FINAL ratio to figure the roll out if I'm using the spur gear as the reference; the ratio changes with different clutch bells. When I use the manual's technique, I get an incorrect speed (150+MPH). Why would I need to use the final ratio to calculate roll out if I have the sensor on the spur gear?
Maybe you could shed some light on this: Internal ratio (diff/crown gear): 3.30 Pinion ratio (clutch bell/spur): 4.43 = final ratio: 14.52.
Wheel diameter is 5.5 so 17.27 is the circumference. If I use a roll out from the internal ratio, I get 5.2. If I use roll out from final ratio, I get about 1.2.
When I use 1.2 as the roll out, the speed seems closer to correct (still off though) but: I'm using the spur as pickup, not the clutch bell. Clutch bell size shouldn't make a difference if I'm taking the reading off the spur gear... Please throw me a bone here. Either this thing is not calibrated at the factory, or I'm doing something totally wrong.
Dave
QUESTION: When figuring out the roll out, do you use the car's INTERNAL gear ratio (3.3) or the FINAL ratio (14.5). I have the sensor mounted to pick up off the spur gear. Why would I use the FINAL ratio to figure the roll out if I'm using the spur gear as the reference; the ratio changes with different clutch bells. When I use the manual's technique, I get an incorrect speed (150+MPH). Why would I need to use the final ratio to calculate roll out if I have the sensor on the spur gear?
Maybe you could shed some light on this: Internal ratio (diff/crown gear): 3.30 Pinion ratio (clutch bell/spur): 4.43 = final ratio: 14.52.
Wheel diameter is 5.5 so 17.27 is the circumference. If I use a roll out from the internal ratio, I get 5.2. If I use roll out from final ratio, I get about 1.2.
When I use 1.2 as the roll out, the speed seems closer to correct (still off though) but: I'm using the spur as pickup, not the clutch bell. Clutch bell size shouldn't make a difference if I'm taking the reading off the spur gear... Please throw me a bone here. Either this thing is not calibrated at the factory, or I'm doing something totally wrong.
Dave
01-31-2007, 10:17 PM
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RE: Spektrum Telemetry - "ROLL OUT" Issue
Mine is way off too...I used the method A option where you measure the distance your car travels in ten revolutions of the spur gear. My distance was 51" which means I should enter 5.1 into the roll out screen. Now my handhel unit is telling me that my car is going 600-1200 MPH. Whatever. Should have bought the Nomadio.
03-04-2008, 10:42 PM
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RE: Spektrum Telemetry - "ROLL OUT" Issue
when i did the roll out it came up with 50" so i put in 5.0 and it was way off. I divided the math the other way, 10/50 and came up with .2 wich seems way closer when it displlays the mph but havent tested it to be accurate.
03-05-2008, 11:35 AM
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RE: Spektrum Telemetry - "ROLL OUT" Issue
It may well be the problem that you are using the spur gear then. If the manual says to use the CB, then that's definitely it. The reason is by changing the CB teeth, you change the rate of rpm of the spur for the same given distance. If sensor points to clutch bell, you will always be getting the engine RPM, not after it's been reduced by the teeth of your gearing.
