Excel worksheet for some of my speed runs
 

Here's an excel worksheet for some of my speed runs.

http://home.comcast.net/~youngsongdmd/speed.xls

You can simply change the KV, and voltage, pinion, spur to get your speeds. The voltages are odd because they're adjusted so the MPH match the actual speeds. Speeds were measured with GPS.

If you don't have Excel, there is a program that you can use to figure out speed:
http://www.waits.net/public/rcgears/
It's the one that I use.

Hey, MetalMan, That RC Gear program is pretty cool...

the excel sheet I use, is pretty accurate to it.... Less than 1% difference... :)

I've compared this calculator to my actual GPS tested results and have found something to be quite off by an average of 9.4 mph.

For example, my 8S powered Rusty at 22/84 "should" hit 53.4 mph on 10 cells at 1.05V, but "actually" only hit 40.5 mph ... a big difference of 12.9 mph.

Does this mean that I'm doing something wrong (calculations or actual testing), or that the calculator doesn't include real life items like weight and wind resistance?

those calcuations are based on a perfect condition... you know... in a vacuum...

now, you have to think about inertia.. wind resistances... voltage drop.... Bearing and Gears Resistance... Tire Tread resistance...

there are some things you must take into consideration... :)
I hope that helps you figure out why...

Gotcha .. that's what I was thinking.

So .... for use in real-life testing, do you just assume a certain variable of difference, like 10 mph or something?

yeah. that's what I do... but I think the the more wattage motor you have.. it'll be a small gap... know what I mean....

but 10MPh is a good number... but with the 8s, you should be well over 40mph...

swami-rc got his to over 48 mph with 10 cells and 18/90 gearing.. but he was using a rusty....

why don'tyou get the basic 5300, that thing will take you close to 70mph....

I'm using a Rusty as well, but with 10 cells and 18/84 I'm only getting 35.3 mph. I wonder what he's doing different with his Rusty to have 13 more mph than me.....

holy crap...you got some problems...i run 6 cells on a novak ss5800 in one of my t4s and i get 35 and we all know how weak the novak is

Got to get me one of those 22 series from Santa! :D

No, these speeds are not best case scenario. That's the whole point of the voltage drop from 1.2 to 1.05 per cell. As a matter of fact, see how my voltage drops from 29.6 volts to UNDER 21 volts when running my emaxx under extreme gearing?

Honestly, I gotta agree with sleepy23 - you got some problem with your batts, gearing, motor, or something.

A 5800 in my B4 went over 43 mph with 6 cells!!!

There must be something wrong with something.

I finally broke 51.3mph, but it took 12 cells geared at 27/84! The spreadsheet says that combo should take me to 77mph. Ummmmm ... nope. :)

The controller temp was 105F and motor was 150F. I tried 10 cells and 12 cells with 18, 20, 22, 25, and 27 Tooth pinions on an 84T spur.

I am baffled. This same controller (BK9918) with my 9L took my e-maxx to 45 mph geared at 22/66 on 14 cells, and that's dang close to what lipomax's spreadsheet says. Hmmmmm.... that tells me the controller and cells are fine.

Actually ... I am now thinking the problem is that these calculations are based on 32P gearing, while I'm using 48P gearing. The diameter of a 60T spur at 32P is way bigger than at 48P. How can I update these formulas for 48P gearing? Nope that doesn't make sense. Gear ratio is gear ratio regardless of pitch. Blast!

Thanks for reading my novel ... :-)

I have to say that there is definately something wrong with your setup. In my Rustler, I have a Feigao 540 size 12s. When I did speed runs with 4s Lipo, the motor was only pulling about 40,000RPMs MAX at full throttle. I got up to 56.5mph... And that was with 25/87 gearing (or something like that). I am sure I could have gotten it to go faster, but the space I had was VERY limited (as in I have about 100-150ft. for acceleration, and 50ft. for braking).

That said, your motor on 12 cells should be spinning at about 56,000RPMs at full throttle. With high gearing and with enough space to accelerate to full speed, you should be hitting pretty close to 60mph. But if you don't have at least 300ft. for acceleration, you aren't going to do it. For the car, the difference between 50mph and 60mph is HUGE, and so it will take a lot more time to go from 50-60 than from 40-50 (air resistance). Also, if you run with a body, take it off and then run it. The body is actually more likely to slow it down. When I did my speed runs, I never ran with one. Another thing to check is your slipper clutch. For speed runs, you want it tightened down completely. Also, if your tires aren't getting good enough traction, they could be slipping from the enormous power.

Now, if none of this helps, than I am dumbfounded. The only other thing it could be is gears/bearings.

Thanks for the reply ....

I've got a great place for my speed-runs. It's a brand new industrial road, smooth and level, very wide, straight, and forever long ... with absolutely zero traffic. :-) I go from as far away as I can see to as far away as I can see (and still be able to control it.)

I've tried with the body on and the body off as well and I made sure to tighten my slipper completely.

I am seriously dumbfounded. I know there's no binding because I can push it quite easily with my finger. My batteries are always 125F when they peak.

I even checked the motor today to make sure it was the 8s.

Any ideas?

maybe it's ur batteries.. gears.. bushings?... :)

Kulang Do you think you may have got the wrong motor? Mistakes do happen. Some thing don't add up with it. Have your tried to figure up if you had a 9 or 10s if it works out right.

Well, I know it's not my batteries because I have tried four different sets of matched GP3300s. When I charge them on my Integy 16x4, they still get about 3200-3400 mah charged at 5 Amps.

Gears, bearings, etc .... I know there's no binding and it sounds fantastically smooth, much smoother than my e-maxx.

Wrong motor? That's an interesting thought. Reverse calculations on Lipomax's spreadsheet show that my motor is performing as if it has a kv between 3400-3600, not the 4436 that's stamped on it. The Feigao 10S has a kV of 3549. Interesting thought! My truck is running exactly as if it had a 10S in it according to the spreadsheet.

Is there a way that I can find out if this motor was incorrectly labeled/stamped by the manufacturer?

You can do it if you have an oscilloscope. I wouldn't be able to tell you how to measure the kv even with one. If you are really interested, a search on Google might help you out.

Another idea would be to get a Venom Speed meter. Use it to gauge your speed while your car is off the ground, and when at full throttle, measure the speed of the car and the voltage of the batteries. You can use this measurement in determinging what the kv is by using your gearing (assuming you put the sensor on a drive shaft). This isn't as involved as using an oscilloscope, and should be pretty accurate, but you will have to pay for the speed meter.

You could measure the amp draw under no load situation. Each motor draws slightly different amps under no loads. You can find the data at motocalc for the no load draws. In addition, are you sure you got the right gear ratio for the tranny? The right size tires?

My tires are Pro-line dirthawgs that are exactly 4" tall.

The Rustler final drive ratio is 2.72:1.

I am seriously beginning to think that I have the wrong motor. I think I have a 10S that's marked as an 8S. That would explain everything.

I don't know how to measure amp draws under no load. I think my multimeter only measures in volts and ohms.

This is making me crazy! :C:

If your multimeter has a DC amps setting, you can measure the motor's no load amps. What you would do is hook your multimeter in series with either the positive or negative wire to the controller. Then rev the motor and see how many amps the display shows. Feigao's website has the no load amp ratings on all of their brushless motors.

The rpm/volt on the Feigao motors is also under no load. The loaded rpm/volt of the 8s is actually slightly less than 4000(3990?). This, and some battery voltage drop makes a lot of sense to me. With aggressive gearing, the voltage is probably .9-1 volt per cell. This, along with the 3990 rpm/volt figure probably makes a lot of sense on paper(spreadsheet). I would certainly expect higher speeds than you are getting, though. I am curious how well your batteries are deliovering the voltage under load(not all gp3300s are created equal-mah after charging has nothing to do with voltage under load, either).