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OpenBarbell is a device with a retractable string that attaches to your workout equipment to deliver data such as speed or range of motion.

For more information and examples of the OpenBarbell in use please see our Instagram or other links below.

Are you an OpenBarbell owner or contributor? Visit WikiBarbell if you have any questions. If you can’t find an answer head over to the forum and ask away.





OpenBarbell V1.0 Owner’s Manual
Check out the OpenBarbell Buildlog
Check out the WikiBarbell

Frequently Asked Questions

Basic Info

How much will OpenBarbell cost?

We are trying our best to keep the price low enough to allow the amateur lifter to enjoy the benefits of Velocity Based Training. At the same time, we’re balancing unit costs and the amount of time spent on our part designing and assembling small batches of these units. That being said, we are offering OpenBarbell for sale at $199, an order of magnitude less expensive than comparable devices.

When will OpenBarbell be released?

OpenBarbell will be released on our webstore on Sunday, February 21st at 8:00 PM Eastern! They will go fast, so we recommend you keep an eye on the OpenBarbell countdown here and on the home page.

Does my device have a warranty?

The Squats and Science OpenBarbell is unlike most consumer devices available for purchase. It was made by a couple engineers who were fed up with the lack of accessibility for advanced training tools and decided to solve the problem themselves. That meant making something that works quickly and at low cost. Although we would love to continue to support our devices as long as you own them, we will only be making these in small batches and therefore unable to replace parts, dedicate a service team or absorb the costs of return shipping. We will however support each and every device when it arrives on your doorstep, and if there are any issues you can ship it back to us to be repaired or we will give you a full refund.

OpenBarbell, like the name suggests, is also totally open source and Arduino compatible. Normal warranties prevent users from hacking their devices, but we encourage it. We do not wish to preclude you from modifying your device and we hope you have the ingenuity to create functionality that the community can take advantage of.

That being said, we do plan on helping our owners wherever we can. Any questions you have about your device can (or may already) be answered in the Owners forum. If the forum doesn’t help and you’re feeling frustrated you can also send an email to the dedicated account This service will never expire and as long as we have fingers (and money to pay for hosting) we will be replying to your forum posts.

What does OpenBarbell do?

Very simply, OpenBarbell measures the position and velocity of an object in one dimension. This capability allows a lifter to utilize VBT (Velocity Based Training) to autoregulate their exercise routine. Autoregulation is a fancy way of saying you use the most current information about how strong you are to determine what you do at the gym that day. This type of training has been shown to be incredibly effective at both executing long term training goals and planning maximum effort attempts in the same day.

How do you use OpenBarbell?

Coming soon!

Technical Questions

I'm getting funky battery readings, is that alright?

OpenBarbell is made primarily by two engineers. In order to get these devices out in a reasonable amount of time, we decided against doing in-house battery conditioning. What that means is your OpenBarbell needs to learn its battery over the course of the first few charge and discharge cycles. We highly recommend you charge it until full as soon as you get it, and let it discharge until 2-3% without letting it die. You’ll notice it has much more consistent battery readings, and will appear to last much longer.

What are OpenBarbells dimensions?

80mm (width) x 90mm (height) – Approximately.

What's under the hood?

OpenBarbell is powered by a Nordic nRF51 series ultra low power SOC. This system is a combination of a 2.4 GHZ Bluetooth transceiver and a low power 32 bit ARM Cortex -M0 core. This package is mounted onto a board developed by RF Digital called the RFduino, which is Arduino compatible and FCC Module Certified for use in consumer electronics.

What are the maximum and minimum velocities?

The following are theoretical numbers from our experimentation. We will likely do further investigation and will post them here.



The maximum velocity can be answered in a few different ways. If you wanted to know what the fastest barbell lift is that it can track, the answer is ALL OF THEM! In our testing we haven’t been able to approach a skipped reading or measurement with any barbell lift, no matter how strong our subject is an how light the weight is. We can be relatively sure of this because, our velocity code runs in what’s called an ‘interrupt’, which checks the encoder at a rate close to the clock speed (16 MHz, or 16 million times per second). The bottle neck is how fast it can crunch the numbers after the interrupt occurs, and by comparing how many times we get in the interrupt vs. how many times we crunch the numbers, we can tell when reps are missed.

If you want to know how fast you can pull the string out of the device, first I would say please don’t do anything you would regret, then I would say we have pulled the string as fast as 5.71 m/s average velocity and 12.62 m/s peak velocity. The fastest lifts I’ve ever seen are hovering around 2 m/s average velocity. The bottleneck would likely be the mounting point of the spring and the axle, so if you were to attach it to a bottle rocket or an SR-71 Blackbird that’s where we’re guessing it would fail first. We’ve tried and failed to do it with any of our humane means.



The minimum is a little more straightforward, although a bit mathematically involved. Let’s pretend we’re coaching the worlds smallest lifter. His bench ROM is incredibly short and he has been training for decades, carefully refining his technique becoming the worlds slowest lifter.

Our hardware calculates velocity approximately every 2.8 mm. Velocity being distance over time, the smallest possible distance you can travel would lead to the slowest possible velocity. Coincidentally, our tiniest lifter in the world has a bench ROM of 2.8 mm.

Our ARM Cortex M-0 processor has a time-based interrupt that is constantly counting upwards in microseconds (millionths of a second). Because of the limitations of a 32 bit unsigned long variable, the number rolls over every 70 minutes and starts counting from 0 again. Since the odds of you starting and ending a rep at that exact time are incredibly slim, we did not write code to fix that fringe case. That means the maximum time we can do one rep would be about 70 minutes. That happens to be the longest attempt our World’s tiniest lifter has ever accomplished.

A little bit of math later and we’ve calculated that the tiniest lifter in the World has maxed out our device at an astonishing 0.0000006667 m/s. That is roughly the equivalent of traveling the distance of one wavelength of red light every second.

How accurate is OpenBarbell?

There are two metrics that are important when talking about the quality of data you get from OpenBarbell. Those are accuracy, and precision. Accuracy is how close our readings are to real-world velocities, which we discern from lab grade velocity measurement devices. Although accuracy is very important, we often get the argument that precision is even more valuable. A precise device would produce readings that are always consistent with each other, allowing you to compare lifts to those done in the past and future, which is vital for autoregulation.


OpenBarbell is both very precise and incredibly accurate. We have preliminary results from measurements made against the Tendo device, OptoTrak optical position sensing device, precision micrometers and super-high accuracy industrial encoders. Our readings show that we have the capability to reproduce real-world velocities very consistently, with R-values above 0.999 and accuracy hovering around 98-99%. Don’t take our word for it. Dr. Mike Zourdos at Florida Atlantic University is currently conducting a validation study on the device with the results to be published later this year, or early next year. We will also publish official results of our own test soon as well.

How long does OpenBarbell last on a charge?

With our real-world testing, we are currently estimating that, using your device’s energy economically, it can be trained with every day and last about a month. With a normal training schedule it could last even longer than that. The lifetime of the battery should be great as well, since that is dictated by number of charge cycles and there can be as little as 10 a year!


Please keep in mind, personal use can vary. If you tend to leave your device on between workouts you can kill the battery in a matter of days. If you turn it off between sets it will last much, much longer.

What's the maximum displacement?

The maximum string displacement is under 9 ft. In real world scenarios, that means a lifter about 6’6 can do an overhead press with a close grip and only have a few inches to spare. If you’re very tall, tread with overhead work carefully in the beginning. If you’re doing presses you can mount the device higher off the ground. If you’re doing Olympic Lifting you can mount it on a few extra plates until it’s just below the bar, and be careful not to run off the platform. If you have a habit of doing that, we will be developing a magnetic attachment that will release if pulled too far. Check our store for that in the future!

How much resistance does this add to the bar?

OpenBarbell adds up to 1/3 lb to the bar. That is when pulling hard at close to the extent of the string length. This is consistent with other draw-string based devices.

How does my device work?

Coming soon!

My device is acting weird while plugged in. Is it broken?

It’s perfectly fine! OpenBarbell is chock full of peripherals so we needed to use pins for multiple purposes. Two pins that are grounded while the MicroUSB are plugged in are vital for the devices functionality.


We understand this may be inconvenient, but we’ve designed it to charge fast and last long, so hopefully it won’t be so bad!

Servicing and Repair

What happens if a part breaks or malfunctions?

If your item breaks or is in need of a specific part, you have a couple of choices. OpenBarbell is totally open from head to toe so from day one you have the ability to modify, improve, or fix your own device. Search the forum or write a post and we will instruct you on the best course of action. If it turns out we have the ability to supply a spare part or can fix it ourselves, you can send the unit to us and we will fix it at no cost (but we cannot cover the shipping). Since the device is also totally open source, we hope others who may be more technically inclined can pitch in to help others in case of VBT emergencies.

What happens if my string breaks?

OpenBarbell is made with a very durable half millimeter Kevlar string. It has been tested for almost a year in these devices with very little signs of wear. That being said, we know somebody out there will put the string through the gauntlet so we installed a few fallback solutions.

A common area of wear for the string is at the top where it rubs on the bar. If you see it getting precariously thin, you can cut it off and tie the bar clip lower. There are a few extra turns of string on the spool, so you can unfurl a turn or so and you won’t lose any string travel. There will be a tutorial for this soon!

If you need to restring the device, the entire center assembly comes off and you’ll have access to the spool. A tutorial will be available for this as well.

Are my magnets supposed to spin in place?

Don’t worry, nothing is wrong with your unit. In our effort to allow easy disassembly, we used screws at the bottom that do not have nylon locking nuts. They’ll stay put, but over time they will move around by a fraction of a turn. This doesn’t impact the units ability to maintain its magnetic attachment to a ferrous base object. We encourage owners NOT to tighten these bolts, as you can over-tighten them and cause the top part to break.

How resilient is OpenBarbell?

We hope you’ve noticed how sturdy OpenBarbell feels, but we hope you also know that this device is hand made by the Squats & Science team and isn’t your ordinary consumer device. It was built to be kept in your gym bag and will last as long as you keep good care of it. Think of OpenBarbell as a fine hand made sports car. It’s beautiful, high performance and rock solid but you probably shouldn’t go off-roading with it.

Why is my spindle wobbly, and is that OK?

We evaluated several manufacturing techniques for OpenBarbell. The laser cutter turned out to be our best bet for a high accuracy low cost device. The problem with laser cutters is the optics create a conical beam for cutting, not the super straight laser beam people imagine.

Laser beam cutting edge.

This causes the edge of some parts to be a little crooked, and moving parts to be a little wobbly. We evaluated this fact when deciding to use laser cutting for our manufacturing and it doesn’t effect the accuracy or consistency of our device in any way. For more information about how our device works, see the “How does the device work” question.

Hacking your device

How do I hack my device?


We’re glad you asked! OpenBarbell is Arduino compatible, has a totally open source design and a completely open source app (if it’s not released, we’re working on it!). That means there are a ton of ways you can tinker with your device! To start off, visit the OpenBarbell V1.0 WikiBarbell for in depth information about how your device is made. There, you’ll see a full rundown of the OpenBarbell hardware and how to go about modifying it safely.

If you’re looking to hack the firmware head over to the RFduino Readme on GitHub to get started. You can play with the velocity detection algorithm, send more robust velocity data to the app, display all kinds of information to the screen, program visual cues at certain points of the lift, create a visual metronome for tempo squats, the opportunities are endless!

If you’re looking to hack the app, which is where we think the most exciting features can be implemented, check back here soon for more information as we are deep into development as we speak. If you think you can help the team we’d love to hear from you, send us an email at

Does this stuff void my warranty?


Remember, OpenBarbell doesn’t have a standard warranty. It comes with very limited support (outlined above) and a 14 day return policy. That being said, I can split this answer into two sections.


If you decide to modify the hardware and break something, we will do our best to make you replacement parts (at close to cost) but we cannot guarantee you parts or fix your device for you for free. We build the device to last, but we can’t compensate for your possible lack of DIY skills. If you NEED to hack the hardware or manufacture your own replacement parts, our housing and PCB CAD files are all available via our GitHub page.

Firmware & Electronics:

Again, we aren’t sure how good your hobby electronics skills are, so we can’t guarantee our board can make it through bouts with your soldering iron. Upgrading your battery, adding LED’s, installing a buzzer are all things that we would not be able to support if it were to go wrong. The same goes for firmware, if you are clever enough you can probably find a way to burn out your PCB via firmware change. We will however support any upgrade to official Squats & Science firmware updates. If you verify that your issue was caused directly because of a firmware update we will do our best to correct the situation.

How do I update my firmware?

Updating firmware is a little involved, and not for the faint of heart. If you’re familiar with Arduino and can navigate a breadboard it isn’t too bad. It requires the following parts:


One OpenBarbell

One MicroUSB Breakout Board

One RFduino USB Shield (or other FTDI board)

One Breadboard

Jumper Wires


  1. Follow the guide here (scroll down) to both install the Arduino IDE (if you haven’t already) and RFduino compatibility.
  2. Grab the latest firmware from our GitHub.
  3. Download the OpenBarbell required libraries and paste them into your Arduino libraries folder.
  4. Put together your breadboard
    1. Wire the MicroUSB breakout to the RFduino USB Shield in the following configuration (MicroUSB Breakout –> RFduino USB Shield) (see the RFduino USB Shield schematic here)
      1. D+ –> GPIO0
      2. D- –>GPIO1
      3. ID –> RESET
      4. GND –> GND
      5. VCC –> +3V
    2. Plug the RFduino MicroUSB Shield into your computer, go into the Arduino IDE and navigate to Tools –> Board and choose “RFduino”, and select your COM port (you may need trial and error to pick the correct one).
    3. Plug the MicroUSB Breakout into your OpenBarbell.
  5. Upload code!