DIY Electromagnet Start Gate

Solenoid start gates make for consistent heat starts.
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gpraceman
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DIY Electromagnet Start Gate

Post by gpraceman » Sat Sep 28, 2019 1:05 am

I haven't really been satisfied with my jury-rigged solenoid start gate setup for my Micro Wizard Freedom track. I use that track use for about 15 Awana races a season. I just hadn't made the time to build something better. I've seen some gravity gates that some of the league guys have come up with. No springs or rubber bands to snap the gate open, causing a lot of vibration to the track, just gravity. I definitely wanted a new gate like that. Then I saw Chuy's electromagnetic gate that he posted about on the NPWDRL forum. I really like the design and especially the electromagnetic release. That inspired me to get off my duff and build myself a new gate.

After a bit of trial and error, I've got the mechanical part of the gate done (photos below). The MW track isn't as easy to attach things to, like the Best Track, with its hardware channels. So, I came up with my own hardware channels, using some leftover channel that I had in my workshop for making up various woodworking jigs. I mocked it up first on some 1/4" MDF. Then I made up a mounting plate with 1/8" x 3" aluminum plate, complete with clinch nuts to make mounting/unmounting to the track easy. I tried some off-the-shelf brackets to hold the start pins to the main rod, but those were too short. So, I got some 1/2" x 1/2" aluminum bar stock and made my own. Set screws hold the brackets to the main rod and hold the start pins.

The start pins are actually 8mm stainless steel straws which came with colored silicone tips. Those tips will hopefully keep the pointy nose cars from slipping off the start pins. Some lesser quality stainless you can stick a magnet to, but not to these, fortunately. So, no worries if someone ever decides to stick a magnet in their car's nose. I had started out with solid start pins, but was concerned about dampening the pendulum action, with more mass being swung around. Some dampening is necessary to keep the pins from swinging back through the holes in the track. We wouldn't want some car, that is really slow off the start (e.g. a bad wheel issue), get popped off the track by the pins swinging back and catching the bottom of the car. :eek: To dampen the swing, I used a memory foam ear plug. That works perfectly. Memory foam absorbs the impact quickly but rebounds slowly, making the dampening nice and gentle.

I tested out the electromagnet by rigging it to a power supply. I wasn't sure just how strong it would hold. A spec sheet doesn't really give much assurance that it will hold back 4 outlaw cars, weighing up to 1 lb each. I was quite surprised at how well a 5V electromagnet will hold, even with our heaviest cars loaded on it. It takes a good amount of hand strength to break the release lever free.

Now to work on the electronics. I'm going to use a small micro controller board from Adafruit, with a relay to power the solenoid. Just like with Chuy's gate, I'll have a key fob remote release. I'll also have a remote switch that can be plugged in, to be the backup triggering means.


I had to draw it out to make sure the pin swing would work out and figure out how long my pin holders and start pins needed to be.
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Side view - latched
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Side view - unlatched
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Top view
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Bottom view
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Here you can see the purple memory foam ear plug. It is stuck in a hole of a little corner bracket. Easy to change out, if necessary.
Image


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.

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Re: DIY Electromagnet Start Gate

Post by Loud2ns » Sat Sep 28, 2019 8:03 am

Looks great! Nice work.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sat Sep 28, 2019 10:52 am

Loud2ns wrote:
Sat Sep 28, 2019 8:03 am
Looks great! Nice work.
Thanks!

One other detail that I forgot to mention. I thought that cutting the steel rod and flat bar would be a pain, but I went and got one of those metal cutting diamond blades for a circular saw and put it in my chop saw. It was a 10" chop saw, but I could only find a 7" blade. It worked out very well, nonetheless. Just let the blade do the work and it went through the material pretty quickly. I used a 10" - 80 tooth blade that is capable of cutting aluminum as well as wood to cut the channel and pin holders.


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.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sat Oct 12, 2019 12:32 pm

Making progress on this project. Though, I've run into some parts issues which have slowed me down on getting the electronics done. I've got most of that resolved. Two out of the three ways to trigger the gate are working. Triggering from a local push button and a remote corded push button are working. I need to get a replacement RF receiver module, since the one I have isn't working. Once that is resolved, I will be able to trigger the gate with a key fob remote as well. On resetting the gate, I've made it so when the lever is raised back up (and thus closes the start switch), the electromagnet will automatically come on.

On one side of the controller, there's the power jack, power LED and gate connection (to the start switch and electromagnet). The other side has the local trigger button, jack for the remote trigger button, trigger LED, and a phone jack. I can plug the start switch cable from my Fast Track timer into the phone jack. It looks a bit messy with all of the wires connecting the components together, but there is a cover to the enclosure that will eventually hide the mess.

Image


Randy Lisano
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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.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Mon Oct 14, 2019 1:18 pm

I checked the new gate with my simulated Best Track start line section and it will work with that brand of track with only a couple of minor changes.

1. Longer start pins, due to the height of the BT extrusion.
2. Different mounting holes. I figure just two bolts inserted into the inner hardware channels on the two outer lanes would be sufficient. I don't like storing a start gate mounted to a track, as I have seen gates and start pins get damaged in storage, so it is good to be able to easily remove the gate.

Image


Randy Lisano
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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.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Fri Oct 18, 2019 10:44 pm

Got the controller fully working, so this project is now complete. If anyone wants more detail on this project, PM me. I've got schematics, parts lists, and firmware code.

Some improvements over Chuy's design:
1. Multiple ways to trigger the gate (local button switch, corded button switch, keyfob remote).
2. Electromagnet turns back on automatically when the gate is manually reset.
3. Compatible with Micro Wizard and Best Track tracks.
4. Position of the electromagnet being at the end of the start lever provides a bit more holding power.
5. Latching relay used, so relay doesn't need to energized the entire time that the electromagnet is on, saving some power. A 10ms signal will latch/unlatch the relay.
6. Can be directly interfaced with commercial timers, to provide the start signal. This one is setup to work with Fast Track timers, but could easily support other brands of timers.

With 3 ways to trigger, I have a lot of flexibility. If I have a problem with the keyfob, there is the corded switch. Worst case, there's the local switch. I can also use the corded switch in tandem with the keyfob. I've had racers jump the gun and trigger the gate before we've finished our traditional 3-2-1-Go countdown. I could make it so I have to be pressing the corded switch before the keyfob will work. That would be a minor change to the programming of the controller.


https://youtu.be/nnMGWJlflJU

Finished controller. It's got a small microcontroller board from Adafruit. Stacked on that is a latching relay board. There's also a RF module for keyfob activation and a protoboard to help connect everything together. If I had to do it over, I would use a different RF module. One with a relay, like this one. The one I used worked on +5V, while the controller works on +3.3V, so I had to use a voltage converter to get the signal down to the right level.
Image

One side of the controller has a power jack (micro USB), a power LED and a connection to the gate (start switch and electromagnet).
Image

The other side has a local push button switch, a jack for a corded switch, a trigger LED, and a phone jack for timer's start gate switch cable.
Image


I did a bit of vibration testing with the new gate and the OEM gate. The gravity gate cut vibration significantly over OEM. I might be able to improve that a bit by adding in a 2nd memory foam damper.

OEM Gate - Max vibration was 7.0 MMI
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Gravity Gate - Max Vibration was 4.6 MMI
Image


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.

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Re: DIY Electromagnet Start Gate

Post by Speedster » Sat Oct 19, 2019 6:12 am

If the system should fail is there a way to start the cars without electronics and loss of time?



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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sat Oct 19, 2019 10:13 am

Speedster wrote:
Sat Oct 19, 2019 6:12 am
If the system should fail is there a way to start the cars without electronics and loss of time?
I will keep the old gate in my gear box as a Plan B. So, if the electronics for the gravity gate fail for any reason, it is an easy swap out. Just two screws.


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.

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Re: DIY Electromagnet Start Gate

Post by Speedster » Sat Oct 19, 2019 4:06 pm

Thank you. Sounds like a really Great set up. Are you going to offer these for sale for the Best track?



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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sat Oct 19, 2019 4:12 pm

Speedster wrote:
Sat Oct 19, 2019 4:06 pm
Are you going to offer these for sale for the Best track?
No, Doc Jobe owns a patent on gravity gates. This was just intended as a DIY project for use on my Micro Wizard track for the races that I run for local Awana clubs.


Randy Lisano
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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.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sun Oct 20, 2019 11:12 am

If I get enough interest from people wanting to build their own controller, I could come up with a custom PCB that would make connecting up all of the components much much easier. It would eliminate much of the wire nest inside the controller.

I did actually design the controller so that you could use it with a regular solenoid. Then you could take advantage of the multiple ways of triggering the solenoid. You would likely need a separate power supply for the solenoid. The relay in the controller would switch that on to energize the solenoid. The electromagnet for my system works on 5V and doesn't use much power, so a 2nd power supply wasn't necessary.


Randy Lisano
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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.

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Re: DIY Electromagnet Start Gate

Post by gpraceman » Sat Nov 16, 2019 12:24 am

The new gate got its first test in battle tonight. It performed very well. Unfortunately, when I tried the keyfob triggering earlier in the week, it wasn't working. So, for the race I ended up just using the remote push button switch. That worked perfectly. I'll have to look for a more dependable radio receiver.


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.

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