Start Gate: Laser or Micro-Switch?

[Packdude]

Microswitches have a few disadvantages: They take a pounding, they must be mounted with fairly close mechanical tolerances, and they are prone to switch bounce.

I would agree if the switch is mounted in such a way as to be activated by the start gate hitting it as it releases the cars. However, the way our switch is mounted, it is activated by the gate moving away from it. There is very little impact when the gate is reset for the next race.

[John Shreffler]

It is still lots of bumping around. Microswitches have even been used as the finish line detector. Not very successfully, however.

I used to supply microswitches with The Judge. There were enough problems with this component that I took a careful look. I now supply mag switches, and have not received any complaints for years now. Hard to get anything gentler than a tiny magnetic field nearby. And hard to beat mounting tolerances of plus or minus 1/4 inch. I will send you one to try out if you want.

[Stephen's Dad]

Hey John,

You have mail.

We would be more than happy to purchase your magnetic switch if you can get one here in time for our March 25th PWD.

Steve

[Packdude]

I sent you a pm John with my address. I would indeed like to test your switch. I'm assuming it will work with my DT8000 and Daytona timers? As I mentioned in the pm, we had some issues at this weekends derby, false races, if you will. I'm wondering if this could be a combination of the micro switch and a new, inexperienced person working the start gate. I wouldn't have suspected either before reading this thread...

[Stephen's Dad]

We just installed a very strong 120 VAC gate solenoid (Dormeyer 2536-M). Rather than using a lot of levers & such I found this heavy duty unit that has a full 1" of pull travel. Now I'm concerned about the magnetic field that it creates.

How far from, a strong electromagnet should these switches be located?

[John Shreffler]

The lamination of the relay pretty much contains the mag field, although it would be prudent to separate the switch as far as practical. As long as you are using electricity to operate the gate, why not interface the relay power to your finish line? Then you would not need a switch at all!

[gpraceman]

Then you would not need a switch at all!

I think that each device (timer, solenoid, light tree) should work independently. If you have a problem with one, then making them dependent will mean that you cannot use the other device(s).

Also, if there is variation in the amount of time it takes a solenoid to open the gate (due to the solenoid or the linkage to the gate), that variation will show up in the race times. Better to have a switch mounted to the gate so you don't have to worry about that issue.

[John Shreffler]

Both solenoids and spring-loaded gates have this in common: They cause the pegs to completely disappear into the slots before the cars even think about moving, assuring a perfectly fair start, and rendering moot any timing error from this source.

[gpraceman]

assuring a perfectly fair start,

I've worked in a manufacturing environment and have seen solenoids stick before, even slightly, so I wouldn't trust the signal to activate the solenoid as the event to start timing. Each device should be independent IMHO.

[Stephen's Dad]

Good News! The magnetic switch is here. I'll go down to the laboratory & see how it works this evening.

John brought something up in a private email that I was aware of but think it is prudent to share.

With the current mechanical gate switch our Micro-Wizard timer resets to ZERO once the start gate is returned to the closed position. So we aren't using a push button to release the gate. Rather we have a toggle switch that must remain in the "gate open" position until all of the lanes have finished racing or the times won't be recorded.

I'll report back tonight after testing.

[gpraceman]

With the current mechanical gate switch our Micro-Wizard timer resets to ZERO once the start gate is returned to the closed position. So we aren't using a push button to release the gate. Rather we have a toggle switch that must remain in the "gate open" position until all of the lanes have finished racing or the times won't be recorded.

Yes, that is something to keep in mind with that brand of timer. You cannot have the gate auto reset itself until the race is over. Most implementations of a solenoid that I have seen just pop a latch to open the gate and do not then raise the gate back up.

I actually find it useful to use a micro switch with any of the Fast Track timers. In situations were a car does not finish, all you have to do is raise the start gate to the up position and the timer will then stop timing and send the results to the race software. Some of their timer models do not support receiving software commands to quit timing and send the results so the race software cannot tell the timer to quit timing. However, all of their timers will send the results if the start switch is closed so they will not be left waiting on the last lane(s) to finish. This does not apply if using their laser gate.

[John Shreffler]

For Microwizard finish lines, I install a time delay circuit, which has no delay for the start, but delays the re-close of the reset by 5-6 seconds, allowing all cars to cross the finish line. This makes it easy to use solenoid power to substitute for the switch.

[gpraceman]

For Microwizard finish lines, I install a time delay circuit, which has no delay for the start, but delays the re-close of the reset by 5-6 seconds, allowing all cars to cross the finish line.

That would have been a problem in a few of the races that our pack has run for other packs. We have a 48 ft long track and have had several of the slower cars finish in the 6 to 8 second range (barely making it across the finish line). With a 5-6 second delay, these cars would be shown not to have finished at all since the gate would have been closed and the timer would send no times for that lane(s). With a shorter track, that delay would not likely be an issue, but on ours it would.

This makes it easy to use solenoid power to substitute for the switch.

It may make it easy, but I still would not advise it. Each device should be independent. A problem with one device (technology is great but it cannot be counted on 100%) should not mean that you cannot use another device.

[John Shreffler]

The green light is on for 3.0 seconds so the total hold-off time is about 9-10 seconds, good for the longest tracks, although your point is taken.

Another thing that must be considered with 120VAC solenoids is to make sure any failures do not put the juice into the computer circuits or into a metal track. Do your switching with optically isolated solid state relays, and make your linkage non-conducting.

[Hot Rod 1]

We just had our pack race this past weekend with our new 450 Challenger track from Beta crafts. The timers were Fast track from Microwizard with Lazer gate. The lazer was hard to keep adjusted at first. It would moveeverytime the start gate was activated. But found that a HOT glue gunfixed that problem. Even after teardown and reset up Lazer was perfect Alignment and work great.