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 remote control 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.
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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.

Loud2ns
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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.

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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 » 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.

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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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