Solenoid Start Gate Circuit

Discussions on buying or building timers, solenoid start gates, light trees, weigh scales, and other race related electronics.
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Solenoid Start Gate Circuit

Post by *5 J's* » Thu Oct 14, 2010 10:00 am

Below is a circuit for a start gate operated by GPRM via the serial port.

12Vdc will be supplied via a 12Vdc AC adapter (500mA or greater). Most people probably have one kicking around or you could order one such as this 12Vdc AC adapter. Note which size plug it is using. This one is using a 2.5mm, so I would need a 2.5mm female jack such as this 2.5MM DC JACK, PANEL MOUNT.

C1 is a 3300uF capacitor and is used as low-pass filter to clean the 12Vdc power.

S1 is the solenoid. I have two options. This one has a 1/4" pull or this door lock actuator which has a 3/4" pull. NOTE: Solenoid did not have enough power - ordered this one instead

D1 is a diode and is reversed biased in the circuit. It is used to shunt the current developed as the field of the solenoid collapses.

Q1 is an N-channel MOSFET and is used as the switch.

R1 is a 100k resistor and is used to prevent noise for triggering the MOSFET.

D2 is another diode and is used to prevent current flow towards the serial port on the computer.

I have also incorporated a normally open momentary switch (SW1) that can be used to "manually" operate the solenoid.

Image

Operation is as follows: The +12v will be applied to the circuit but will sit on the drain of the Q1 MOSFET. GPRM will send the open start gate command to the gate on the MOSFET via pin 4 of the DB-9 connector. One this voltage is applied to the gate of Q1, Q1 will allow current flow from the drain to the source. This will activate the solenoid, allowing the start gate to open. Once GPRM stops sending voltage to the gate of Q1, Q1 will stop conducting and the solenoid will return and it's collapsing field will be shunted via the D1 diode.

This can easily be modified to have a light tree trigger the solenoid vice GPRM.

My plan is to integrate the wires from pin 4 and pin 5 of the DB-9 into the wires running between the RJ-11 jack's used for the gate switch on the Microwizard timer, such that I only have one 4 conductor wire running between the start gate and the timer. Then one serial cable from the timer to the computer.

What do you all think? Is there anything I am missing or other things I should integrate? This should me a relatively inexpensive mod for my track. Should be about $10 in parts plus shipping costs.

I am not sure what "device" the solenoid will pull on to open the gate. I like the lever Sporty is using but I'm not sure where I can pick one up. I could easily make something I suppose.
Last edited by *5 J's* on Mon Nov 01, 2010 1:41 pm, edited 2 times in total.



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Stan Pope
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Re: Start Gate

Post by Stan Pope » Thu Oct 14, 2010 10:30 am

As it stands, the pulse shape of the current through the solenoid matches the pulse shape from the input. It may be undesirable for the solenoid to be actuated for more than a half second depending on how much power it requires.

If you don't know the input pulse shape from the serial port or want to control the duration of the solenoid activation, you can add some shaping between D2 and Q1. A series cap to transform the level to a pulse and a cap parallel with R1 to limit the duration of activation.


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Re: Start Gate

Post by *5 J's* » Thu Oct 14, 2010 10:39 am

Stan Pope wrote:If you don't know the input pulse shape from the serial port or want to control the duration of the solenoid activation, you can add some shaping between D2 and Q1. A series cap to transform the level to a pulse and a cap parallel with R1 to limit the duration of activation.
Randy states "The trigger signal is +12V and will remain on for the amount of time that you specify in the Hardware Options screen. There is no pulsing of the signal, just on or off."

So I guess I would want to set it to 0.5 sec or less.



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Re: Start Gate

Post by Stan Pope » Thu Oct 14, 2010 10:53 am

Yes! Since the input shape is known and acceptable, my suggested additions would be unnecessary complication!


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Re: Start Gate

Post by *5 J's* » Thu Oct 14, 2010 10:57 am

Stan Pope wrote:Yes! Since the input shape is known and acceptable, my suggested additions would be unnecessary complication!
well, I'm not sure the shape, and I don't have an o-scope, but I'm guessing it would be nearly a square wave.



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Re: Start Gate

Post by Stan Pope » Thu Oct 14, 2010 11:36 am

But you know enough about the shape (low v., high v., and duration) that further complication is unnecessary.


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Re: Start Gate

Post by *5 J's* » Thu Oct 14, 2010 11:43 am

Stan Pope wrote:But you know enough about the shape (low v., high v., and duration) that further complication is unnecessary.
True.



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Re: Start Gate

Post by *5 J's* » Mon Nov 01, 2010 1:37 pm

Here are a couple of pics of the start gate I'm working on. The solenoid above didn't have enough pull so I ordered this one. Should be here in a couple of days. The linear actuator worked fine, but it's a bit big for the mounting bracket I had aleady made. I will use the actuator for our Pack track. All the components except the solenoid and capicitor (filter) are mounted, but I'm going to wait and solder after the solenoid comes in. The red button on is a "manual" over ride. The start gate connects to the timer via the phone jacks (two wires for the gate trigger and two for the gate switch. Note: the timer connects to the computer via the serial port. (see here for timer)

Image
Image



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Re: Start Gate

Post by Darin McGrew » Tue Nov 02, 2010 6:05 pm

I have a couple thoughts looking at the gate. The first thought is that the board contributes a lot of rotating mass. A lighter gate would have less rotating mass, allowing it to open more smoothly.

The second is that the gate can rotate only 90° or so before the hinge stops it. It could open more smoothly if it were able to rotate about 180° before the hinge stopped it. Instead of a configuration like this:

Code: Select all

____________________

track
____________________
    |      |O----
    | gate || hinge
    |______||
It could be a configuration with an extra board the same thickness as the one in the gate, like this:

Code: Select all

____________________

track
____________________
    |      |       |
    | gate | board |
    |______|_______|
       ----O----
         hinge



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Re: Start Gate

Post by *5 J's* » Wed Nov 03, 2010 5:04 am

Darin - I had contemplated using an aluminum start gate similar to the one on a Freedom Track , but thought I would try the solenoid on the wood gate first.

What do you think would benefit most - going with a thinner wood with less mass, or installing the additional block and rearranging the hinges to allow the gate to open 180 degrees? Note that currently the spring stops pulling at 90 degrees.



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Re: Start Gate

Post by FatSebastian » Wed Nov 03, 2010 8:17 am

*5 J's* wrote:What do you think would benefit most - going with a thinner wood with less mass, or installing the additional block and rearranging the hinges to allow the gate to open 180 degrees?
Why not both? Our homemade test track incorporates both of Darin's suggested features. Our board and gate in Darin's illustration is low mass, cut from an extra-large paint paddle / stirrer (just thick enough to be able to hold the hinge screws).
*5 J's* wrote:Note that currently the spring stops pulling at 90 degrees.
The gate will fall under its own weight without a spring; a spring is needed to pull the pins away a little faster than the cars accelerate. Once the pins have gained sufficient rotational acceleration, the work of the spring is no longer needed. By reducing the rotational mass of the gate, one should be able to get by with a lesser spring, hopefully reducing any bounce problem. Allowing the gate to continue its swing-through (not under spring tension) should help even more, as gravity and hinge friction take away some of the rotational energy.



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Re: Start Gate

Post by *5 J's* » Wed Nov 03, 2010 8:46 am

FatSebastian wrote:
*5 J's* wrote:What do you think would benefit most - going with a thinner wood with less mass, or installing the additional block and rearranging the hinges to allow the gate to open 180 degrees?
Why not both? Our homemade test track incorporates both of Darin's suggested features. Our board and gate in Darin's illustration is low mass, cut from an extra-large paint paddle / stirrer (just thick enough to be able to hold the hinge screws).
*5 J's* wrote:Note that currently the spring stops pulling at 90 degrees.
The gate will fall under its own weight without a spring; a spring is needed to pull the pins away a little faster than the cars accelerate. Once the pins have gained sufficient rotational acceleration, the work of the spring is no longer needed. By reducing the rotational mass of the gate, one should be able to get by with a lesser spring, hopefully reducing the bounce problem. Allowing the gate to continue its swing through (not under spring tension) should help even more.
Must be a thick paint paddle or some really short hinge screws. What are you using for starting pins FS? I am using #10 stainless screws, so I would want enough thickness to securely hold the pins. Initially my gate was a spring closed which has been "simply" converted to a spring open (you can still see the blemish from the old spring position in the picture). I may try some using some thinner wood and rearranging the hinges to allow 180 degrees of rotation. I may change to a much lighter spring as well, though it's hard to find one that is strong enough to maintain shape, yet light enough to suit the needs. I may just go to an aluminum gate if I'm going to put much work into this.



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Re: Start Gate

Post by FatSebastian » Wed Nov 03, 2010 9:30 am

*5 J's* wrote:Must be a thick paint paddle or some really short hinge screws.
Both are ~1/4". (Consider large paint paddles free from the Orange Box.) You can also reinforce the hinge/plate assembly with adhesive later as necessary.
*5 J's* wrote:What are you using for starting pins FS?
~1/4" wooden dowel. I drilled a hole in the wooden pin plate for the pin and securely glued the dowel in the hole.
*5 J's* wrote:I may try some using some thinner wood and rearranging the hinges to allow 180 degrees of rotation.
I believe it would be a relatively easy and inexpensive thing to try.
*5 J's* wrote:I may change to a much lighter spring as well, though it's hard to find one that is strong enough to maintain shape, yet light enough to suit the needs.
We went to rubber bands. Varying the rubber band size, doubling them up, etc., gives one great ability to adjust the tension just right. Rubber bands don't have the longevity of springs, but they are easy enough to replace every season or so.



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Re: Start Gate

Post by *5 J's* » Wed Nov 03, 2010 10:07 am

FatSebastian wrote:
*5 J's* wrote:I may try some using some thinner wood and rearranging the hinges to allow 180 degrees of rotation.
I believe it would be a relatively easy and inexpensive thing to try.
*5 J's* wrote:I may change to a much lighter spring as well, though it's hard to find one that is strong enough to maintain shape, yet light enough to suit the needs.
We went to rubber bands. Varying the rubber band size, doubling them up, etc., gives one great ability to adjust the tension just right. Rubber bands don't have the longevity of springs, but they are easy enough to replace every season or so.
Yes, it's definitely easy and inexpensive to try, I just try to minimize any drilling or screwing into melamine board. For the start gate and timer in installed brass inserts that accept #8 machine screws.



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Re: Start Gate

Post by Darin McGrew » Wed Nov 03, 2010 12:42 pm

As I mentioned before, it's been a while since I've looked at our start gate. But here's what I recall:

The "pins" are cut from an aluminum bar (about 1/8" thick, 1" wide), and are long enough to extend the the diameter of the "axle" they're attached to, the gap between the "axle" and the track, the thickness of the track, and the height of an uncut derby body block with wheels mounted to it. The "axle" is a dowel about 1/2" in diameter, which has been flattened slightly where the "pins" are attached. The pins are attached with tiny bolts that run through the dowel and through the aluminum. There is very little rotating mass, and the gate can rotate about 270° before it stops.



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