[RikoRocket]

OK, just did the maths. delta velocity is sqrt 2x9.81x1.81 = 6m/s so it will vary +/- 3m/s from the average.

So if your average speed is 12.5m/s then peak at the bottom will be 15.5m/s and at the top 9.5m/s

 

[Dr_C]

my estimate based on school kid physics... (hopefully)...

change in kinetic energy = change in potential energy

{1/2 m v(bottom)^2 } - {1/2 m v(top)^2 = m g h

where:

m= mass
g = accel of gravity
v( bottom) = velocity at bottom of loop
v(top) = velocity at too of loop

then if we substitute

v(bottom) = v+u
v(top) = v-u

we get:

{1/2 m (v+u)^2 } - {1/2 m (v-u)^2 } = m g h

simplifies to...

2 v u = g h

or

u = gh/2v

then we put in the numbers...

u = 9.81 x 1.81 / (2 x 12.5) = ... ? ... m/s

i didnt even use the sfi equation editor function

 

[Giblets]

To put it another way, in laymen's language: if my maths are correct,12.5m/s equates to about 27.96mph ... which is actually faster than the average speed you clocked on that lap you did at Mt Panorama in the 1:1 Mustang last year

 

[Dr_C]

Yes... fast is certainly fast... but I am also interested to learn what speed an NSR-F1 with Evo King 50 motor on a 12m drag strip can reach... it will be interesting to compare with Ricks amazing loop... lets see...

c

 

[RikoRocket]

Nah DRC, my way - the potential energy gets converted to kinetic energy, so potential energy = kinetic energy. Your original equation is correct

So mass cancels out and you get 0.5 x velocity squared = gravitational acceleration x height

I'll go slowly here

velocity squared is therefore 2x gravitational acceleration x height

so velocity is the square root of (2x gravitational acceleration x height)

gravitational acceleration is 9.81m/s2

height is 1.8m

velocity is the squareroot of (2x9.81x1.8) m/s

squareroot of (36) is 6 m/s

simples!

 

[Dr_C]

In that case I need to draw on the first law of online physics... never disagree with a moderator

c

 

[RikoRocket]

OK, I bow to the professor, mine assumes it accelerates at 9.81m/s2 for 1.8m. But the faster it is going the less chance the car has to accelerate.

 

[injectorman]

To put it another way, in laymen's language: if my maths are correct,12.5m/s equates to about 27.96mph ... which is actually faster than the average speed you clocked on that lap you did at Mt Panorama in the 1:1 Mustang last year

The embarrassing bit is I think you may be right.

 

[injectorman]

So to all you maths geeks at which point exactly do I place the speed detector to get maximum speed???

 

[RikoRocket]

right at the bottom. But, it makes no odds, although DRC suggested it makes a significant difference to the speed, by his calculation its less than 1m/s

 

[Dr_C]

At the bottom of the loop and the speed will be slightly faster than the average so use a trackside speedometer if you want accuracy.

c

 

[Dr_C]

i calculate the value of u as 0.7m/s

so at the top it would be 11.8m/s and at the bottom it would be 13.2m/s. So doing the trials at the very bottom will get you the highest speed but check precisely with a speedometer. I consider +/- 0.7m/s quite significant if accurate measurements are to be attempted.

c

 

[300SLR]

I calculate the value of u as 0.7m/s

so at the top it would be 11.8m/s and at the bottom it would be 13.2m/s. So doing the trials at the very bottom will get you the highest speed but check precisely with a speedometer. I consider +/- 0.7m/s quite significant if accurate measurements are to be attempted.

Agreed.

The flywheel effect of the motor etc will reduce the difference a little, I didn't bother to calculate that but guess the above figures are a near enough approximation.

 

[Dr_C]

Yepp, and we are also assuming that effects of electrical energy input can be ignored because the cars are close to their max speed - so most of that energy will be converted directly into heat (in one form or another e.g. Ohmic or friction generated).

c

 

[300SLR]

Come to think of it, how about trying a simple way of eliminating the speed difference. Lay the track on it's side so the car is going round like a "wall of death" motorcycle. The only difficulty is getting it started, once it's up to a very modest speed it'll go round no trouble, The speed will be constant round the lap, so timing laps and taking the average will give an accurate answer.

The more you think about it the more things you think about that might make some difference between bottom and top of a vertical set up. For example at the bottom it's got the car's weight added to the centripetal forces and at the top the car's weight is subtracted from the centripetal forces so there's more drag at the bottom. The current on his meter and the hot smell from the motor tells us there's plenty of drag.

 

[shorty54]

I am no aerospace engineer, very far from it, but I am just wondering if air temperature, humidity, barometric pressure, and/or altitude would have any changing effects of the test?

Let say, I build the same test rig with the same setup and I test in my yard would I get the same results?

Right now its,

-13C

Barom 1035bm

Dew point -17C

Humidity 70%

Enjoy,

Shad

 

[Dr_C]

Wow... with those temperatures I would want to use electricity to heat my gloves rather than heat a fast moving little slot car motor

c

 

[Ade]

All good points and interesting stuff

, but even at 10ms it's way above what's ever actually raced at in the "real" world ..

 

[Dr_C]

Test Rig currently being built to test up to 15m/s across all id, no it won't be a rug racing affair but purpose built .
As we know Scorpius already tested at 10m/s and passed with flying colours :thumbsup:

I thought this thread was about sharing ideas and progress to establish a method for testing slot cars at speeds in the range 10-15m/s. Assuming the plan is to reach the upper end of that range i.e.15m/s then some collective ideas and knowledge sharing may help? right?

We all like slot car bones to chew over... especially those that are race speed related...

c

 

[Ade]

who said the goalposts have moved

just back from afternoon Sax practice