Speed Calculations with Voltage Drop Complication
After a bunch of searching, I found a formula a couple weeks ago where I can calculate the top speed of my Mini-Baja. I was also lucky enough to find the tranny gearing ratio and tire diameter for my foamies. However, a complication arises when you take into account the voltage of my Li-Po pack. I have a 3s 1320mAh lipo that on the first charge held 12.7v. Actually, that was pretty high, considering the excellent documentation that came with it (Thunder Power) said that it should be holding about 12.6v max. I have a feeling people are doing calculations based on the nominal voltage of battery packs and not the peak charged voltage, because Castle Creation's own "how fast will my mini-t go?" PDF lists a top speed near what my calculator lists for 11.1v, and not the peak of 12.7v.
Now here is where it gets tricky. Everyone knows that battery packs drop in voltage when a huge load is placed on them. How much is the question? I can certainly throw a multimeter in there and give the throttle a stab and see the drop, to get a more accurate calculation of the top speed, but with no load on the drive train that's not very accurate. To be more accurate, I suppose you could place the car on a slick surface and do a sort of burn out, but even that is not as accurate as the load given during acceleration on dirt or asphalt. But you can't just strap a multimeter to the car, it's too big, and it's really heavy--changing the load even more! So does anyone have a relatively accurate estimate of what the voltage drop would be? IIRC have I seen little on-board telemetry boxes that measure this??
Top speed for my setup should be 42mph with a 15t pinion, 5400 mamba, and 3s lipo assuming no voltage drop. Not bad! What is more impressive is the wheelie at any speed ability! 1/2 ounce of lead on the front should help with that and net me faster acceleration next time out. Did I mention I love tuning? lol
Link to calculator (sorry, crappy host): [link]http://upload2.net/page/download/HP1mzI5tXHhNKAy/bajagearing.xls.html[/link]