Calculate car speed.

DIY timing systems
User avatar
SlartyBartFast
Master Pine Head
Master Pine Head
Posts: 272
Joined: Mon Feb 12, 2007 11:30 am
Location: Montreal, Quebec

Calculate car speed.

Post by SlartyBartFast »

After a hiatus, I'm back with ridiculous questions... 8)

If a timer were to capture the time of both changes of state as a car passed through the gate, and if all the cars were measured for length, would it not be possible to report car speed at the finish line?
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

SlartyBartFast wrote:If a timer were to capture the time of both changes of state as a car passed through the gate, and if all the cars were measured for length, would it not be possible to report car speed at the finish line?
I suppose you could, but checking length for each car, recording it and then using that measurement to calculate speed of each run, seems like more work than it is worth for a race.

Anyways, speed when crossing the finish isn't as exciting of a figure as the average speed over the course of the whole track length (start pin to finish) or peak speed. It is easy enough to get the average speed, but it would be cool to try to figure out what the max speed was.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
User avatar
ohiofitter
Master Pine Head
Master Pine Head
Posts: 693
Joined: Sat Feb 03, 2007 10:30 am
Location: Uniontown,Ohio

Re: Calculate car speed.

Post by ohiofitter »

I'm not a math-a-matition but I believe that you should be able to divide the feet of your track by your time should put you in the ball park.....hence 32/2.5=12.8............that should be 12.8 feet per second than convert that in to MPH....maybe Stan can chime in with a helpful tip....I know pine design give you a estimated mph..but how close it is I'm not sure.plus I found this site that might help.http://www.onlineconversion.com/
Last edited by ohiofitter on Sat Nov 29, 2008 10:17 am, edited 1 time in total.
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

ohiofitter wrote:I'm not a math-a-matition but I believe that you should be able to divide the feet of your track by your time should put you in the ball park.....hence 32/2.5=12.8............that should be 12.8 feet per second than convert that in to MPH....maybe Stan can chime in with a helpfull tip
That gives you the average speed. The max speed a car attains and the speed when crossing the finish line are ones that are not readily found with current timing systems. The average speed will be between these two values.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
User avatar
ohiofitter
Master Pine Head
Master Pine Head
Posts: 693
Joined: Sat Feb 03, 2007 10:30 am
Location: Uniontown,Ohio

Re: Calculate car speed.

Post by ohiofitter »

Hey gpraceman.....could you place more timers on a track at lets say middle of the drop section.....right and the transition one on the middle of the flat and the finish line....I don't know if there's software that would let you record all the values onto a computer but you would get different speeds at these points would you not
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

ohiofitter wrote:Hey gpraceman.....could you place more timers on a track at lets say middle of the drop section.....right and the transition one on the middle of the flat and the finish line....I don't know if there's software that would let you record all the values onto a computer but you would get different speeds at these points would you not
You could always set something like that up with custom hardware and software. However, you are still getting an average speed of the car from the start line to the timing position.

What Slarty was proposing was to time from when the car first blocks the sensor to when it no longer blocks it and then calculate the speed at that point. Track length would not matter, only the length of the car. That gives more of a true speed at that point on the track, instead of an average speed.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
User avatar
ohiofitter
Master Pine Head
Master Pine Head
Posts: 693
Joined: Sat Feb 03, 2007 10:30 am
Location: Uniontown,Ohio

Re: Calculate car speed.

Post by ohiofitter »

Well can you scale down the car...........they have to be 1/25 scale roughly...............there's got to be a simple math equation for this
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

ohiofitter wrote:Well can you scale down the car...........they have to be 1/25 scale roughly...............there's got to be a simple math equation for this
Scale only comes into play if you want "scale speed"; otherwise, you get true speed.

There isn't a way to calculate the true speed at given points on the track unless you add sensors at various points and then measure as Slarty proposed. That is not something that off the shelf timing systems will do. A custom system would need to be developed or some kind of radar gun system.

Current timing systems will start timing based on a signal from a start gate switch or sensor and then finish timing when a car blocks a finish sensor. That gives you the time that the car took to travel from the start line to the finish line. During that stretch, the car's speed builds (acceleration down the ramp), hits a peak (just before the transition) and then slows (along the transition and flat), so all you really get is an averaged speed across that full run distance.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
User avatar
ohiofitter
Master Pine Head
Master Pine Head
Posts: 693
Joined: Sat Feb 03, 2007 10:30 am
Location: Uniontown,Ohio

Re: Calculate car speed.

Post by ohiofitter »

What about the hot wheels radar gun..........I know there cheap and they say they work.and you tube has a guy that dismantled one and made it bigger using house hold items..( I THINK) but you'd have to search forhttp://cgi.ebay.com/HOT-WHEELS-RADAR-GU ... 240%3A1318
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

ohiofitter wrote:What about the hot wheels radar gun..........I know there cheap and they say they work.and you tube has a guy that dismantled one and made it bigger using house hold items..( I THINK) but you'd have to search for it.
A radar gun would give you a speed of a car at a certain point. I would wonder just how accurate a toy gun would be. You'd also need one for each lane.

Speed at a certain point(s) doesn't tell you who wins, so I don't really think it is a useful figure. One car could be slowing down more than an other, towards the finish, but not get nosed out before it crosses the finish. Looking at only speed at the finish would give a misleading result.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
User avatar
ohiofitter
Master Pine Head
Master Pine Head
Posts: 693
Joined: Sat Feb 03, 2007 10:30 am
Location: Uniontown,Ohio

Re: Calculate car speed.

Post by ohiofitter »

I see what you mean....these things are like 14-30 bucks on ebay......I would think you could get you final speed at the finish line...........also reading on them a little you have to clock them head on it sounds like
User avatar
SlartyBartFast
Master Pine Head
Master Pine Head
Posts: 272
Joined: Mon Feb 12, 2007 11:30 am
Location: Montreal, Quebec

Re: Calculate car speed.

Post by SlartyBartFast »

gpraceman wrote:so I don't really think it is a useful figure
Useful? Who cares. It's more data for the dataheads. :lol:

And my idea would be to include sensors at different points on the track. Debating whether to calculate speed based on car length or having two track sensors do the work.

Seeing as all kinds or car data is collected anyways as part of inspection...

For those that like analysing data, you could tell who leads at what point, the speeds, who slows down too much over the flat, lot's of fun analysis you could do.

Even final speed is interesting. You can guess if the car that won caught up or if a losing car would catch up given how much more distance.

I don't see the point in using a radar gun, even if it's just to get final speed, when there are already sensors on the track.

As for difficulty measuring, I already have the jig designed. Piece of track, one fixed post, one mobile post. Mobile post connected to digital micrometer (14$ on sale). Thing even has a computer link.

Just adds recording the length (or pressing a button computer connected) to the standard inspection jig for length, height, wheelbase...
User avatar
Stan Pope
Pine Head Legend
Pine Head Legend
Posts: 6856
Joined: Sat Jul 05, 2003 7:01 pm
Location: Morton, Illinois
Contact:

Re: Calculate car speed.

Post by Stan Pope »

gpraceman wrote:The max speed a car attains and the speed when crossing the finish line are ones that are not readily found with current timing systems. The average speed will be between these two values.
That is really counterintuitive! Are you sure it is correct?

Average speed is certainly less than max speed. Considering the time spent getting down the ramp (accelerating from 0), it seems unlikely that the average speed would be greater than the finish line speed ... unless the track were quite long or the car were extraordinarily lossy.
Stan
"If it's not for the boys, it's for the birds!"
User avatar
gpraceman
Site Admin
Site Admin
Posts: 4926
Joined: Fri Jun 20, 2003 12:46 am
Location: Highlands Ranch, CO
Contact:

Re: Calculate car speed.

Post by gpraceman »

Stan Pope wrote:That is really counterintuitive! Are you sure it is correct?

Average speed is certainly less than max speed. Considering the time spent getting down the ramp (accelerating from 0), it seems unlikely that the average speed would be greater than the finish line speed ... unless the track were quite long or the car were extraordinarily lossy.
I would expect that the average speed would be faster than the finish line speed. The car rapidly accelerates to max speed and then the speed tapers off from there until it crosses the finish. I really don't see how the average speed would be less than the finish speed. The only way I could see that is if the acceleration to max speed was quite slow.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
NealOnWheels
Apprentice
Apprentice
Posts: 23
Joined: Thu Mar 30, 2006 11:38 am
Location: Rolling Prairie, Indiana

Re: Calculate car speed.

Post by NealOnWheels »

Two sensors placed a short distance apart could do the job and would be car length insensitive.

Place such a system at the finish line and you get the finish speed.

Place such a system at a point along the track where max speed is expected and you get an approximation of the max speed. On a typical track that point may be the transition from the slope to the flat.

Or do this at both points and use the data to determine the "lossiness" of a car.
Post Reply