ZZ Speed calculations Part I

[wild03]

In this series I will attempt to prove that is better to be quiet and be thought a fool, than to speak and remove all dough.
It was 3am the other night and it hit me, I could actually calculate the expected speed of my ZZ if I did a simple calculation. I took a rough measurement of the wheel diameter with a Mitutoyo caliper rated at 1/1000 in. that yielded .550 ~ .545 in. Multiplied that times PI ~3.142 to get a Circumference of 1.703 in.
Now we know Motor RPM and gear ratio, by consulting the handy owners manual that comes with each of the cars.

Therefore: I used the following formula,

RPM / RATIO x CIRCUNFERENCE / 12 to get feet per minute.

Here are some numbers for the 12:1 gears and the different motors:

12:1 – 10,000 = 118.26 feet/min
12:1 – 16,000 = 189.22 feet/min
12:1 – 21,500 = 254.26 feet/min
12:1 – 23,500 = 277.92 feet/min

In part II I will be taking some average run times with the different setups to compare the distance traveled with each setup!

In part III I will be adding in friction and drap coefficients to get a speed value closer to the actual value! Yeah right! J

[NorCalCoug]

Eh, don't worry about the drag coefficient too much; theoretically as long as the motor has enough horsepower to overcome any drag preventing the car from reaching its theoretical maximum speed, it will eventually achieve it's max speed.

[tifosi_ms1]

Actually my friend as I calibrate the rear wheels on a clone to be 1.85 inches.

[Steve]

The lap timer I built will tell you the scale speed of the car. As for calculating wheel RPM based on motor RPM, both are total estimates...you have too much going on including gear meshes, chunks of oatmeal on the wheels, cat hair on the axles, tire wear, tread pattern, track surface, rotation of the earth....lap timer

[wild03]

Originally posted by Steve
The lap timer I built will tell you the scale speed of the car. As for calculating wheel RPM based on motor RPM, both are total estimates...you have too much going on including gear meshes, chunks of oatmeal on the wheels, cat hair on the axles, tire wear, tread pattern, track surface, rotation of the earth....lap timer

True, I just wanted to get a comparative estimate of the different gears+ motor setups... Maybe I'll motivate a few youngsters so they can see math can be fun… hehe!

Nice timer BTW, I wouldn’t mind a diagram and a parts list. How do you start the timer? Break the beam to start it, break it again to stop it? For drag racing you'll need one at the starting line and one at the end line....does the software support this? If you drive anywhere but on a straight line I assume that the power required by the turning solenoids will degrade the motor performance!

Can you post some of your times + distance traveled and motor +gear setup! I wanna compare your numbers to the theoretical !!!

Thanks

[tifosi_ms1]

Roughly speaking the top speed for a bit (3.8 and 3.43 to 1 gearing) is 19 mph. Though that is impossible due to the motor having too little torque to move with that gearing. Currently mine is doing 5 mph with 9.85 to 1 gearing.

[Steve]

Originally posted by wild03
...I wouldn’t mind a diagram and a parts list. How do you start the timer? Break the beam to start it, break it again to stop it? For drag racing you'll need one at the starting line and one at the end line....does the software support this?
Can you post some of your times + distance traveled and motor +gear setup! I wanna compare your numbers to the theoretical ...!!!

Yes, for almost everything. I was thinking one could use mirrors to reflect the same beam across the start and the finish lines, but anyway, the software supports 4 lanes (timers), you'll just have to have 4 beams and 4 photoreceptors. A drag racing setup would be ideal for this, as you could have a small speed trap at the end. I only have a touring circuit at the moment. The track length measures 21 feet if you drive exactly in the center, all the way around, which no one does, so kinda like your math calculations, my numbers are really only approximates also. I post lap times in the low 7's with my Zip (red turbo motor and gearing), so I think I get roughly 5.6Mph. Correct me if I'm wrong, I have a mathamatical mental deficiency.

The lap timer was pretty simple to build, I think there are basic instructions in that thread.

[wild03]

Originally posted by Steve
Yes, for almost everything. I was thinking one could use mirrors to reflect the same beam across the start and the finish lines, but anyway, the software supports 4 lanes (timers), you'll just have to have 4 beams and 4 photoreceptors. A drag racing setup would be ideal for this, as you could have a small speed trap at the end. I only have a touring circuit at the moment. The track length measures 21 feet if you drive exactly in the center, all the way around, which no one does, so kinda like your math calculations, my numbers are really only approximates also. I post lap times in the low 7's with my Zip (red turbo motor and gearing), so I think I get roughly 5.6Mph. Correct me if I'm wrong, I have a mathamatical mental deficiency.

The lap timer was pretty simple to build, I think there are basic instructions in that thread.

mirrors? wouldn't you need to split the beam? seems a little hard. I assume you want to wire two photoreceptors in the same line so either could trigger the same timer. If you use two independent laser you'll need to keep the one on the finish line off and once the race starts once the laser at the starting line is crossed you can turn the laser on the finish line on then turn the starting line off...or something like that! tricky!

Ok I'll give that other thread a try, I was hoping for a centralize website to get the software and details...


Thanks

[Steve]

Originally posted by wild03
mirrors? wouldn't you need to split the beam? seems a little hard. I assume you want to wire two photoreceptors in the same line so either could trigger the same timer. If you use two independent laser you'll need to keep the one on the finish line off and once the race starts once the laser at the starting line is crossed you can turn the laser on the finish line on then turn the starting line off...or something like that! tricky!

Ok I'll give that other thread a try, I was hoping for a centralize website to get the software and details...


Thanks

No need to split the beam, all you would do is cross the track with it at the start, then reflect it so it runs the length of the track, then goes back across the track again at the finish and into the photoreceptor. Time starts when the beam is broken initially, and the time is displayed when the beam is broken at the finish. It can be the same beam, and preferrably that's the way to do it. On a circuit track, the same beam is used for start and finish, it's the same place. Trust me, there is nothing tricky about this. If you can figure out the actual speed of your Zip based on a 9.35:1 gear ratio, you can build this thing. The thread has everything you need, but if you have any questions let me know.

[wild03]

Originally posted by Steve
No need to split the beam, all you would do is cross the track with it at the start, then reflect it so it runs the length of the track, then goes back across the track again at the finish and into the photoreceptor. Time starts when the beam is broken initially, and the time is displayed when the beam is broken at the finish. It can be the same beam, and preferrably that's the way to do it. On a circuit track, the same beam is used for start and finish, it's the same place. Trust me, there is nothing tricky about this. If you can figure out the actual speed of your Zip based on a 9.35:1 gear ratio, you can build this thing. The thread has everything you need, but if you have any questions let me know.

Slick Idea !!! didn't think of that one....I did find all I needed on the other thread except pinout information...can you provide what pins you used on a 9pin serial port. you mention not trusting the slot cars website's 1 6 9 8 and 5 ground

Thanks

[Steve]

Originally posted by wild03
Slick Idea !!! didn't think of that one....I did find all I needed on the other thread except pinout information...can you provide what pins you used on a 9pin serial port. you mention not trusting the slot cars website's 1 6 9 8 and 5 ground

Thanks

I had problems with the 9 pin serial ports on my old craptop, so I went with the parallel port and used pins 24 and 14.