Speed Calculator

[Gee]

Brian, I didn't see novak hv 4.5 or 6.5 listed in the motors for your calculations. Do you think 4800 (4.5) and 3100 (6.5) are an accurate kv to use for calculations? Thanks.

[BrianG]

Yeah, that's because Mike doesn't stock those systems in his store. But, yeah, you can just plug in the kv values of any motor you want. The motor dropdown is just for convenience really. If those kv values are correct, then yes, you can use those...

[lincpimp]

Originally Posted by BrianG

If those kv values are correct, then yes, you can use those...

Man, what a smart a$$!

You crack me up Brian

Brian, If I'm running Trakpower packs in a 3 X 2s config. with a Neu 1512 2d. What nominal cell voltage should I choose from the drop down menu? I have been choosing 3.3v.

[BrianG]

Originally Posted by lincpimp

Man, what a smart a$$!

You crack me up Brian

LOL. Sorry, I didn't mean to come across that way.

@Countryhick: It depends on what you are looking for.

If you are looking for a good max speed estimate, use 3.7v and lower amperage (around 20A or so). At max speed, there isn't as much electrical load as at startup.

If you are looking for a decent max torque estimate, use higher amperage and ~3.3v. The most torque will be generated at low rpm. Also, since the highest amperage happens at low rpm at startup, that's where the biggest V drop will happen as well.

[BrianG]

Update to the calc:

- Fixed weight value for the Neu 1512 motors. Was at 360g and should've been 290g. Thanks CountryHick!

- Added differential ratio and spur gear options for the Ofna Ultra GTP.

A planned future addition will include a new page to calculate the proper gear selection when using two speed setups. Probably next week sometime.

[BrianG]

Added the Two-Speed Gear Mesh Calculator.

[BrianG]

Added TrakPower Lipos to the balancer wiring section of the Lipo Wiring page (scroll to the bottom).

Regarding the Two-Speed Gear Mesh Calculator: If anyone knows the formula for calculating the amount of shaft-to-shaft distance you lose by where the teeth meet, let me know. I have most of the code done to calculate shaft-to-shaft distance, but left it commented out until I know this.

[BrianG]

Something I've been toying with is the addition of code to estimate how much speed you lose due to wind resistance/drag. I know calculating this exactly is very difficult due to so many variables, but there's gotta be a rough estimate of speed loss.

Right now, I have a warning box that comes up if the final speed exceeds 45mph. What I was thinking is adding a reduction constant above 45mph. Basically use a formula something like:

mph_reduction = ( calc_speed - 45 ) X 0.4

So, for a top theoretical calculated speed of 60mph, the estimated actual speed would be closer to 54mph: ( 60 - 45 ) X 0.4 = 6mph loss. 60mph - 6mph = 54mph. It's just a matter of finding a constant (currently using 0.4) that is fairly close...

Whaddya think?

[sleebus.jones]

Well, the problem is that the drag is not constant, it's exponential.

However, I did find a neat article here that might help ya out:

http://en.allexperts.com/q/Physics-1...ce-running.htm

[BrianG]

OK, I see that that it's not a true constant... sort of.

So, how about something like:

speed_loss = calc_speed^2 * 0.0015

For 45mph calculated speed, the actual estimated speed is ~42mph
For 60mph calculated speed, the actual estimated speed is ~53mph
For 100mph calculated speed, the actual estimated speed is ~85mph
For 140mph calculated speed, the actual estimated speed is ~111mph

Again, I want this to be just a rough estimation. Basically, I'm trying to develop a formula based on some calculated vs actual speeds from different existing setups. I know, kinda working backwards.

[snellemin]

I would say the calculator is pretty accurate up to around 50-60MPH with the right batteries. For trucks I subtract 10% (drag/resistance/traction loss) at 70mph, 80mph I subtract 30% and 85mph and up the resistance goes higher and higher.

[BrianG]

Added a rough estimate of speed reduction due to wind resistance, drag, etc to the top speed estimator. There is a disclaimer in the help link that says this value is very rough and many variables will affect the accuracy, but it's better than nothing IMO.

Also added power calculations (in watts and HP) to the top speed estimator.

[BrianG]

Updates:

Added a new page to calculate the needed resistor to eliminate the spark when hooking up the battery. It has a very creative name: "No Spark" Calculator.

Also grouped menu items because the list is starting to get a bit long now...

I think it's about time we send Brian some pizzas. What do you guys think?