After finishing the track, I wanted to create a reliable, non-manual starting gate for our wooden pinewood derby track. I noticed that manually releasing the gate caused variations in track time. I experimented with different mechanisms, such as push/pull solenoids with bearings and a key card door solenoid used in locks. However, the weight of the start gate caused too much friction, and it didn't work as I had hoped. I added a Teflon strip to reduce friction and even bearing, but they did not work.
Eventually, I found the perfect solution, which was inspired by an electromagnetic fire door release at my workplace. After some research, I discovered a simple 12-volt electromagnetic lock typically used for cabinet doors. The lock provided the necessary strength to hold the start gate securely and allowed for easy resetting, making it ideal for our needs.
Gravity allows the gate to drop quickly due to the weight of the steel block for the magnetic lock. I was concerned that the gate would swing back up and hit the back of the derby cars before they moved out of the way, but this was not a problem as they were already out of position.
I also found that I didn't have to hold the gate up and then turn the magnetic lock on; I could turn the lock on and then swing the gate back into place. It wouldn't lock prematurely since it needed to be exactly parallel to the locking mechanism to hold tight.
After using the magnetic lock, I quickly realized I needed to add a small latch to keep the gate secure during transport and setup. This also prevented young Cub Scouts from mischievously operating the gate switch. Our first year of building our own track has been a rewarding adventure, and we are excited to share our experience with the Pinewood Derby community!
The start gate was designed to be used from either side, but as you will see below, I only had time to complete one side of the track.
These are the options I tried at first.
Diagram of the starting gate with the electromagnetic lock and position of the microswitch.
The magnet is turned off, and the gate is released.
Here is the underside of the track.
And the schematic for the current wires.
Side view with the connections and switch. I intend to color code these so that people connect them correctly in the future.
Side views of the magnet and microswitch.
Parts list and prices as of May 2024
- Dual Row Screw Terminal Electric Barrier Strip Block 600V 15A 6-Pins - any brand
- $7 for two https://a.co/d/9ui4dIZ on Amazon or eBay.
- Limit Micro Switch, D4MC-5020 (Vertical) or D4MC-5040 (Horizontal) Roller Plunger Micro 1NC+1NO
- $14 Unicel was the least expensive https://a.co/d/3M3mih5
- I wish I had purchased the 5040 model.
- Electric Magnetic Lock, Smart Door DC 12V
- $13 on Amazon (TO BE SECOND brand) https://a.co/d/9iDPFBk
- Power Supply 12V 3A Power Adapter 5.5mm x 2.5mm DC Plug
- $8 (Arybroourd brand) Amazon https://a.co/d/19zNVKM power for Electric Magnetic Lock
- LED Pilot Diode Light, 10pcs, 5mm (5 Colors x 2pcs Diffused Frosted Round Lens) 12V Universal Flush mount
- $8 Amazon https://a.co/d/19zNVKM (has a built-in resistor for 12v)
- I used this set for the finish line timer lights and the extra lights as the power indicator on the start gate.
- DC Power Jack Socket, 5-Pack DC-099 5.5 mm x 2.5mm 30V 10A Threaded Female Panel Mount Connector
- $7 (Adapter- E-Outstanding brand) Amazon https://a.co/d/h1oHuiQ
- I bought other adapters made of plastic that did not work well.
- Electrical Toggle Switch, GSW-110, SPST/ON-OFF, 20 A/125V AC, O Ring/Screw Terminal
- $8 (Gardner Bender brand) Amazon https://a.co/d/gBja7yx
- But just about any panel on/off switch will work.
The level of documentation shared is almost as impressive as the starting gate itself! 