Car Math

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Joey D

Joey D

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Alright so I'm helping my brother out with a school physics project and he wants to caluclate a bunch of stuff for my R/C car. So what he did was make a scale quater mile (40m) and ran the 1/10 scale R/C down the track. He managed to do it in 5.3 seconds at an estimated 168 mph (scale) or 16ish mph(actual). So what he is trying to do is figure out the scale horsepower of the car. We are finding calculators all over the internet but no actual formula. So I know some of you guys have to know this, so could you please help? Thanks.
 
in order to complete 400m in real life cars within 5.3 seconds... well ud need a really, really fast car. I dont think you can measure it in horse power, also because RC cars are real different than cars. But, you could say your simulated car drove a quarter mile in 5.3 seconds.

Only way id think to compare a RC car to a real car... well actually i cant think of anyway to.
 
I could calculate average horsepower, calculating peak horsepower from a quarter mile run will just be estimates. I'm not sure how to calculate scale horsepower, mostly because I don't really know what that means :)

Remember if you want to scale up the weight, you have to multiply by 1000, since weight is a volume thing... 1/10 scale means 1/1000 the volume.
 
Here's my favorite bit of off-topic car math:

pontiacmath.jpg
 
BlazinXtreme
So what he is trying to do is figure out the scale horsepower of the car. We are finding calculators all over the internet but no actual formula. So I know some of you guys have to know this, so could you please help? Thanks.
Click to expand...

I would have thought that you need to find out the power output of your engine (electric motor or petrol/nitro?) then scale it up by 10?
 
If I were doing a physics project on an RC car, I wouldn't mess with all this scale stuff, as it really doesn't have any physical significance.

If it were me, I would do stuff just on the RC car, like make torque and power plots for it. On an electric motor, the torque curve is linear, so it'd be really not very hard to generate both.

Curve looks something like this:

mtdfig19d.gif


Measure torque in in*lbs, power in hamster power or something :D
 
Ghost C
You can do a rough horsepower estimate by calculating weight and quarter mile time, what he's asking for is the formula to do it.

horsepower_equation_et_method_horsepower.png


Source
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Thank you much! That is what I was looking for.
 
Most likely a stock (20 turn) electric car, by the sounds of the numbers. 16mph after 5 seconds seems a little slow for a nirto car. This thread alone makes me wanna fix up the (not-so) old RC cars and test out the top speed, acceleration times, distances, etc.
 
Yeah same... I need a way to measure its speed and whatnot though. I would like to time a simulated 1/4 in my Revo! I can time it, I just wish I had a way to find the trap.
 
Inaccurate. Top speeds are recordable by doing the simple math calculations. Whatever distance divided by whatever time. That's not the hard part.
 
retsmah
You might be able to hook up a bicycle speedometer to it, although it'd be kinda hard to read off of the car :)
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I think they will tell you the max speed after the fact. (Well, the only one I've used did that). Or you could just put a really long wire on the readout.
 
Actually you just do distance/time and it gives you the speed. But after many calculations we figured out that to scale the car should have 3700hp or about .3 real horsepower.

By the way the R/C car has a 14 Double Turn motor that is way over geared.
 
Oh.

I've got a 13 tripple with a 20 tooth pinion. She's pretty friggin' fast, almost too fast for most use. I prefer a Monster Stock.
 
Emohawk
I think they will tell you the max speed after the fact. (Well, the only one I've used did that).
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You're right, I forgot about that. Only problem I could see is that they don't seem to update the speed very often, maybe once or twice a second, which may not be fast enough to catch the top speed. At least mine was pretty slow about updating speed. You could probably do a few runs and get a good number though.


Doing distance divided by time gives average speed, not top speed. Only way that will work is if you set up a second distance after the 40m, and keep the car at a constant speed once it passes the finish line. I guess that'd work, if you have a pretty steady throttle-finger :)
 
retsmah
Doing distance divided by time gives average speed, not top speed.
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Whoops, forgot about that. I was talking about flat out top speed. The car hits top speed pretty quickly, keeping it up there for a few dozen feet isn't hard.
 
I'm gonna measure out 132 feet, but I'm gonna mark off the last 10 meters and measure its 10 meter time there... then figure out meters/second and then calculate km/h from there
 
BlazinXtreme
...He managed to do it in 5.3 seconds at an estimated 168 mph (scale) or 16ish mph(actual).
Click to expand...
I'm not certain that the mph conversion is so accurate. I say that because, provided the full-scale car got good traction, running the quarter mile and trapping at 168 mph is pretty crazy fast. Yesterday I saw a fox body T-Bird run 8.83 seconds at 157 if that gives you an idea. 168 mph trap would probably mean the car is in the low 8 second quarter mile times (approximations up-scaled).... VERY FAST! I just think you should make sure the mph conversion is good.
 

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