Arduino Controlled Power Rack

Do YOU want to get in shape like an Olympic athlete but don’t want to go out in public?? Do you feel like you can’t trust your spotter when you’re squatting 400 pounds? Then Sir/Madam/ Hairless Gorilla do I have a solution for you! The Smart Power Rack! You control the weight, when you loosen your grip on the bar it stops in less time that it’d take your buddy Dave to realize that look on your face isn’t strain, it’s pain. Never need a spotter again (Sorry, Dave), you can train like a techno-savvy shoalin monk in total seclusion. The only questions you need to ask are, Do you really need to get that strong? Do you need to be able to lift several hundred pounds in today’s world? Probably not, but I do know that Black Friday is coming back around and combining this with 6 months of Krav Maga will mean you’ll never lose that 65 inch 4K tv again.

This project began in an engineering class. Being a poor student with a love of fitness and needing an excuse to build my own gym. I seized the opportunity and with the help of my loyal minions, I started drawing up plans. I had four objectives.

1. A bare-bones power rack that could catch the weight faster than a human spotter using a user-controlled switch - as anyone who has hurt themselves in front of others knows, you know you're in trouble a lot sooner than anyone else does.

2. It needed to be dirt cheap. No frivolousness; it needs to be strong, cheap, and gritty.

3. It needed to be safe. The frame needed to be strong enough to hold anything I could feasibly lift and drop with a safety factor of 2.5-3. Max load about 700 pounds.

4. It needed to go above and beyond what you could buy. It needed to be large enough to handle Olympic weight lifting techniques such as Clean and Press.

I'll show you my process (and many mistakes) and at the bottom tips on how to make your own.

This is a project that's designed for stopping heavy weight at a sudden stop. I designed it for my body height (5'8") and max weight when deadlifting (300+lbs). So if making your own, use common sense, and when in doubt, build it stronger. This particular frame could handle loads in excess of 700 lbs (the most weight I could fit on it) and catch a weight before it dropped 2 inches. By adding larger bolts and reinforcing some sections, it could hold up a small car easily.

Be safe, be cautious, and have some friends (or loyal minions) there to help because after lifting this frame by myself so much, I didn't need to go to the gym, I had discovered my own Amish workout plan.

Materials needed

• Arduino Uno
• 1 12v Rechargeable battery
• 2-2 Inch 20ft tow cables (Atleast 1000lb limit each) https://www.amazon.com/gp/product/B00U1OJZEM/ref=...
• 2 25kg/cm high torque servos https://www.amazon.com/gp/product/B076CNKQX4/ref=...
• 12 3/8th inch inside diameter, 7/8th inch outside diameter https://www.amazon.com/gp/product/B01CUNOWWG/ref=...
• 2 counterweights of your own choosing(I used some of my own weight plates)
• 1 12v to 5v variable buck converter https://www.amazon.com/gp/product/B01CE5P33M/ref=...
• 7 Pine 4x4's (DO NOT USE TREATED LUMBER)
• 8 Pine 2x4's
• 2 Spools of wire for the leads
• 2 Strips of velcro
• Lots of screws preferably Torx(Not sponsored but wish I was)
• 1 1.5 inch 0.1-22lb Force sensor https://www.amazon.com/gp/product/B00B887DBC/ref=...
• 6 9 inch 3/8th bolts
• 12 3/8th inch inside diameter Washers
• 16 5 inch 3/8th bolts
• 1 1ft x 2ft 23/32inch plywood
• 2 12in 3/8th bolt
• Nuts, lots of them.
• 2 6inch U-bolts
• 4 Eyebolts with 4 inches of shaft to pass through the timber, eye should be 7/8th inch diameter
• 2 small hooks
• 2 moderately strong springs, strong enough to pull the servo when not powered, weak enough to be pulled by the servo when energized.

I built the frame to fit my apartment and wide enough that the bar would not slam into the frame. So I made the frame a 5 ft x 8 ft base and 7 ft 4 inches tall.

All 4x4's are bolted together using 5 inch long 3/8th inch thick bolts.

All 2x4's are screwed together using 3.5 inch Torx screws.

4 4x4's for the legs with 1 in front overhead and 2 behind, about 15 inches apart.

4 2x4's cut 5ft on the sides

2 2x4's at 8 foot at the base to

You should have a very study box

Make 4 12 inch or a little smaller circles from the plywood.

Drill 1 3/8th hole in the center and 8 3/8th holes equally in a circle about 1.5 inches from the rim. I held 2 panels on top of each other and drilled through both.

Add the bolts and nuts, leave a little more than a 2 inch gap, large enough for the strap to slip between.

Leave one bolt hole in the rim open for now.

I wanted the straps to just wrap around the bar inside the sleeves. My bar was 52 inches between the sleeves so I drilled 4 holes in the fore and back overhead beams each for the U-Rings and Eye beams to give me that necessary distance.

Alright, not all of my ideas went great.

Photo 1: You need at least 4.5 inches of additional material mounted on the reel to create a Counter-reel. It should be between half and 3/4th the diameter of circle of bolts. So if the Main reel is 12 inches and the circle of bolts is 10 inches, the counter reels should be 5 inches. I was running short on time and just added 3 squares of 2x4 onto mine. This was my mistake.

Photo 2: These should be what your reels look like. The left side is where you nail/glue/attach a counter strap and counter weight. It keeps a constant tension on the main strap so there's no slack.

Photo 3: By the time I mounted the reels and had them balanced I realized that the squared counter reels were throwing off my counter weights. I had to make them circular. Didn't feel like taking it all back down so called the minions and told them to start cutting corners, literally.

Photo 4: A photo can say a thousand words, his face says several that only need four letters. Also, you can see how my strap rides over several (up to 8) bearings. In the next step you'll see my updated version.

Photo 1: Start by aligning the spool to the eyebolts previously mounted.

Photo 2. When making the Reel support beams, drill holes 7/8th inches wide into the center of each, then place 2 bearings inside. You can either glue or some other way to hold them in place.

Photo 3: This is the updated design to hold the bolt that the strap rolls on. Instead of directly touching the bolt, mine only rolled on the bearings. This caused several problems. Instead it would be better to mount the bearings directly into the eyebolts. This slightly lowers the cost and stops uneven wear.

When you have everything in place just screw everything down using screws at an angle. Two at the bottom and two at the top of each plank.

Congratulations! If you've made it this far then you've made a very sturdy hammock stand.

Photo 1: Apart from the hammock, you'll notice the three beams at 45 degree angles on the Reel beams. Once the reels are properly balanced, screw the beams in place. This adds more support from it tilting one way or another. It also locks the reels in place so they keep their balance.

Photo 2: Relax and grab a hammock. Now the hard part starts.

Wiring is honestly my weak point. This works but most people can do better.

12 V battery sent through a buck converter down stepped to 6.7 V to the breadboard then sent to the servos.

My battery also had a 5 V USB port which also powers the arduino.

And show some love to this guy who can describe how to use servos much better than me,

https://www.instructables.com/id/Arduino-Servo-Mot...

Of course there's a lovely guide about arduinos and force sensors.

https://learn.adafruit.com/force-sensitive-resisto...

Finally the brakes, I originally had the servos on the backside and the springs on the front.

The arduino receives a signal from the force sensor, then tells the servo to turn 150 degrees. The servo pulls the brake which is constantly in place due to the spring pulling it engaged, the servo overcomes the springs resistance. This allows the reel to move freely.

When the servo is not receiving signal, the spring will pull it back into place, making the brake lock the reel against the spokes.

Photo1: The brakes are simply a piece of 2x4 about 5 inches long with the corner cut off that is facing the spokes.

Photo 2: The Sensor is loosely held in place with velcro after soldering to wires that connect to the arduino.

Photo 3: This was the inspiration for the brake system, a seat belt.

Photo 1: The second set of counterweights are attached to the servo and the break using paracord.

Photo 2: Mount the servos slightly off to the side of the first eyescrew.

The brake only needs to move less than half an inch to disengage the reel, so this simple system works well.

This is the second version I made, haven't had any failures after several workout sessions so next I'll be switching the paracord and Zipties for braided steel cable. I'll measure the lengths of everything under tension then switch out everything for the cable.

1. I used treated lumber. That was the biggest mistake because treated lumber is wet. As it dries, it warps.

2. Again due to the treated lumber, I will have to replace all of my bolts in a year or two as they have begun to corrode due to the chemicals used to treat them.

3. The strap still causes friction on the bar, turning it in your hand. I'll need to find a way to minimize the friction so everything turns smoother.

4. I'd like to remove all of the exposed wires from the project and make it largely wireless.

5. I'd like to make the counter weights either less obvious or uniform, thinking of making concrete cylinders for an industrial aesthetic.

6. Eventually i want to make a better braking system.

Things I've already changed

I switched around servo and spring configuration in my latest video at the top. This way I don't burn anymore servos out due to lock up. It shows how I added another counterweight to the servo side so it still locks when not receiving power.

This is my first completed Instructable, I plan on making many more but I would like your help. If you can give me some tips on how I communicated this Instructable I'd appreciate it. I want to be able to make my ideas as easy to understand as possible, so the more opinions I can get will only help me be a better communicator.

Have a great day and make something amazing!