OpenBarbell was created out of a need for a low cost, accurate, & reliable platform to measure important information about barbell exercises

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OpenBarbell was created out of a need for a low cost, accurate, and reliable platform to measure important information about barbell exercises. Using metrics like velocity and power to analyze and improve upon barbell exercise has been validated for decades by the scientific community. The only reason velocity based training hasn't been adopted en-masse is because of limited access to high quality measurement devices. OpenBarbell aims to change that by initially creating a draw-string based device, capable of industry leading accuracy for (significantly) less than $50. Over time, we hope OpenBarbell will grow to include bluetooth capabilities, a phone app, IMU-based measurements, bar path tracking, and much more.

If you'd like to join our group to develop the initial version of OpenBarbell, feel free to send us an email at We are in need of firmware developers, software developers, and anybody willing to assemble and improve upon early development builds.

Velocity Based Training (VBT) has shown its efficacy in strength science for decades. It affords athletes the ability to infuse their training with highly effective training methods such as autoregulation, one rep max estimation, fatigue monitoring, and has the potential to replace Percentage Based Training (PBT) altogether. Unfortunately, until very recently there has been essentially no affordable solution available for the average lifter to record velocity data. Devices like the Push strength band, Myotest, Atlas and others (.) are bridging the gap, but affordability and accuracy are still a barrier to wide adoption.

OpenBarbell hopes to change that by introducing the lowest possible barrier to entry to VBT. We aim to make a device that is very inexpensive, incredibly accurate, and as simple as possible to use. In order to reach critical mass adoption, we think the open source hardware path is the only way to go for a few important reasons:

  1. The current market is relatively small. It's promising that there is recent investment in products to accomplish this task, but these products tend to dilute base VBT functionality in an effort to increase market applicability, or increase price in proportion to their niche status, or both. If we were to undergo the formal product development process, the same thing would happen to OpenBarbell.
  2. That being said, a good (and cheap) VBT product cannot reach optimal functionality without contributions from the open source community. There are a lot of smart people out there and we hope a small chunk of them are as excited for this tech as we are. If somebody wants to implement Olympic Weightlifting functionality, by all means fork our code. If a sprinter wants to mount it to their starting blocks, and magnetically attach it to their running shoe to measure take-off velocity, go ahead and edit our model files to suit your needs. Rather than pay for development on a proprietary platform, the platform should be open and development can happen around it.
  3. Consumer education is a significant hurdle for VBT. If we can get a small user base to buy or assemble their own OpenBarbell, we can help breed an educated and enthusiastic user base to spread the gospel of data driven training.

  • 1 × Honeywell HLC2705-001 Quadrature encoder IC
  • 1 × Honeywell SEP8706-002 Infrared emitting diode
  • 1 × Teensy LC Arduino compatible microcontroller
  • 2 × Microtivity IM206 Tact Switch Momentary Pushbutton
  • 1 × SSD1306 OLED Module

View all 13 components

  • We've migrated to our official forum!

    seminolemuscle09/03/2015 at 14:50 0 comments

    If you're wondering about the lack of activity here don't worry, the project is alive and well. We've moved our project logging activities to our official build log where you can follow, interact, post questions, and even fork our build and log your own OpenBarbell. You can find all the action here.

    For those of you who don't like clicking links, here's an album of some stuff we've been doing since we've been gone.

  • OpenBarbell Has Graduated from the Shoebox

    seminolemuscle06/05/2015 at 00:30 0 comments

    The OpenBarbell team has been busy...

    As you can see, the prototype has grown out of a shoebox and into a custom 3D printed enclosure. This means we are one major step closer to making an open-source ready project available to those who want to practice velocity based training techniques on the cheap. Some of the benefits of V0.24 are...

    • Portabile
    • Battery powered
    • Arm processor (via Teensy-LC)
    • Low power OLED screen
    • 12 ft. cord (for olympic lifting)
    • Improved UI
    • Kevlar string

    To do:

    • V0.2X Enclosure improvements
    • Battery optimization
    • Bluetooth
    • Remote display (android phone app)
    • PCB
    • Laser cut enclosure (V0.3)

    We have also made some social media gainz with our brand new Instagram page where we will be making more consistent updates than at our hackaday page. Give us a follow and send us a message if you'd like to get involved.

  • Testing and Validation

    seminolemuscle04/01/2015 at 03:15 0 comments

    This week we were lucky enough to make it down to the Muscle Lab at Florida Atlantic University to visit Dr. Mike Zourdos, professor of exercise science and one of the few great minds in powerlifting. Dr. Z has been involved in the many incarnations of OpenBarbell since its inception and once he heard we had a working prototype he invited us over to see what it was made of.

    Glamour shot of the Tendo Unit and Shoebox Prototype #1

    Test setup of the Tendo Unit and Shoebox Prototype #1 on a squat bar.

    Contributor Nate 'the kid' Zephir simultaneously lifting heavy things and doing science.

    The test setup was simple, we hooked up the tendo unit next to the OpenBarbell in close proximity to the inside of the right bar collar (left in the image above) and proceeded to lift all the weights. Since the Tendo unit has been used in peer reviewed publications for years, its output will be considered absolutely correct. After a couple sets, we'd analyze the output of the Tendo vs. the OpenBarbell and dig into the code to iron out kinks.

    Our goal for the day was to reach parity with the Tendo Unit before we left. Our hypothesis before arrival was that our constant representing distance per tic, 2.80 mm, was slightly off and would result in a small but consistent disparity in resulting average velocities. After a few quick sets the data proved us right and we modified the constant to 2.95 mm which had great results. Some more trial and error occurred, some science happened, and we were ready to call it a night. If you're curious to find out if we accomplished our goal of Tendo Unit parity...

    That's about as good as it gets. Due to a couple of physical factors such as placement of the actual units under the bar, it would be impossible for all reps to match perfectly on both units. I'd say on average, we were 0.01-0.02 m/s off of the Tendo by the time we left. It should also be noted that the Tendo Unit has a minimum measurement size of 10 mm where the OpenBarbell currently is at 2.95 mm. We do not know how fast the hardware interrupt on the Tendo Unit operates but OpenBarbell is at a brisk 4 millionths of a second. To top it off, our algorithm records the entire length of the rep, while the Tendo stops recording below a velocity threshold. Given our tech specs, we would not be surprised if our data was more accurate than the Tendo.

    We had a blast at the FAU Muscle Lab, so much so that we plan on going back every Monday until we're happy with the results of the OpenBarbell. Tendo parity is nice, but we want to go further. Keep an eye out on this page for more updates.

  • It's Alive!

    seminolemuscle03/26/2015 at 04:14 0 comments

    Shoebox prototype #1 is complete!

    The measurements are very consistent, and the hardware is showing great promise. There were a couple issues that will be worked out before the end of the week, but we are getting (probably) accurate velocity measurements from a device that is, wait for it, 100x cheaper than the next best alternative. We are getting closer to feeling ready to release all of our documentation and source files but like all good things, you must wait.

    This is a bit unlike other open source projects, in that our goal is to appeal to a group of people that doesn't usually partake in this sort of thing. In order to do so, we need to have a device that can communicate its purpose visually without being too intimidating. Although our shoebox prototype works, it will not provide the spark VBT needs to catch on in the lifting community.

    That being said, if you want your hands on one now or would like to help us expedite V1.0, feel free to leave a comment below or send me a message. We could use plenty of help to get us where we need to go!

    Now for some glamour shots.

  • We haven't been sleeping...

    seminolemuscle03/12/2015 at 05:08 0 comments

    We haven't been sleeping...

    Several prototypes have been made, a bunch of code has been written, and the goal is within reach. This week is crunch time since we set a personal goal to get this working by our competition this Sunday, but next week there will be a detailed update of our progress. There has been a lot!

  • Encoder V0.2 Is Complete!

    seminolemuscle01/28/2015 at 05:25 0 comments

    A lot has happened in the past week or so. We've gone from our first printed part, to two iterations of V0.2 (V0.2 and V0.21) of our working draw string mechanism/encoder.


    GIF of mechanism

    V0.21 is an improvement in clearances so the 3d print needs less hand mods, and an improvement to the spindle mechanism. We also changed the spring from a 12 foot tape measure to a 6 foot tape measure to reduce resistance on the bar. V0.21 was printed but not shown.

    We're also in the midst of V0.3, which will be laser-cuttable for much faster prototype iteration (~5 hour print to ~ 3 minute laser cut). V0.3 will be very helpful in getting as many units out there as possible to OpenBarbell's various contributors.

    Now that the encoder is up and running, we've been able to plug it into an Arduino and take some data. The following data points were grabbed from the serial monitor at 57600 baud. We didn't even hook it up to the interrupt pins on the board, just straight digital in, so we have plenty of optimization to do before we hope to read bar velocity.

    This may not look like much, but it's some of the first bits read from the OpenBarbell project. You can see the string being pulled out, slowing down, reversing direction, and retracting back into the spindle a total of three times. This data will change a lot, as currently we're polling pretty quickly, but in the future we will be getting about half a million to a million looks at the encoder every second, giving us the ability to track both the rising and falling edge of the encoder effectively doubling our resolution.

    Here is the customary optimistic goals for the upcoming week:

    • Improve encoder code
    • Laser cut V0.3
    • Measure reasonably accurate encoder displacement
    • Spit out a velocity measurement

    Number 4 above will the trickiest of them all, because in order to know if we're even close to an accurate velocity, we'll need something to compare it to. We know of one Tendo unit around here, so we may need to pay it a visit.

  • First Part Printed

    seminolemuscle01/18/2015 at 05:40 0 comments

    It doesn't look like much, but it's a big first step to getting our hands on the first dirty prototype. You're looking at the stationary center axle that the spindle, spring and encoder wheel will spin around when the string is in movement. On the right hand side, you can see the thin slit that the reel spring will hook through to anchor itself.

    Some strides were made over the week towards a more 3D printable, and physically feasable set of parts.

    In this version, you will actually be able to put together the pieces,. The U shaped housing can come apart to assemble the spindle/reel spring assembly. Odds are, the clearances are too tight for the precision of our humble Solidoodle and some hand-mods will have to be done. As long as the spindle spins and the encoder reads, we will be in business.

    Full changelog:

    • Added Bottom Plate
    • Changed Axle shape to make it more 3D printable (not pictured)
    • Enlarged Encoder Wheel
    • Fixed pins on Encoder
    • Added pegs for encoder mount
    • Split housing into two parts for easy assembly

    Let the excitement flow through you, for the days of sub-optimal training methodologies will soon be behind us. A new era of velocity based strength training shall be ushered in by one device, one device to rule them all.

  • Possible v0.1

    seminolemuscle01/11/2015 at 05:52 0 comments

    v0.1 is nearly complete. This design foregoes expensive bearings for plastic on plastic rotation. We're hoping the wear is minimal and it would lead to a lower cost device. It was also decided that the center axle should be stationary, since the spring needs something to be anchored to to create the recoil. We could either anchor it to the center axle making it stationary, or anchor it to the side of the housing, letting the axle rotate along with the encoder. It's hard to tell in the image below, but the spindle and the encoder wheel are fit tightly together and will rotate with each other around the center. Barring unforseen destractions, we should have the official v0.1 3D printed this week.

    To do:

    • Make parts more 3D printable
    • Laser cut some encoder wheels
    • Actually make battery powered encoder circuit
    • Print and assemble v0.1

    Plans for the future:

    When we can demonstrate a working prototype (dubbed version shoebox) and can make a decent render so the community doesn't think we're going with a final version in a shoebox, we'll start blasting this page to everybody we know will appreciate it. Hopefully we can snag a few contributors, but we'll be perfectly content with some excited lifters/nerds that want to make a build. Tentative goal is second week of March.

  • The Project Has Begun

    seminolemuscle01/06/2015 at 04:17 0 comments

    The first CAD files have been created! The housing is a rough sketch to get the general idea across, conveying the draw-string mechanism and it's relationship to the optical encoder and the encoder wheel. Additionally, a life size encoder wheel and optical encoder are all CAD'ed up as well, ready to be used to create a 3D printable housing, expected to be ready for electronics this weekend.

    To do (before the weekend):

    1. Finish to-scale housing for electronic components and draw string mechanism.
    2. Create encoder-microcontroller-Li-Ion circuit.
    3. Finish rough first version of draw-string mechanism.
    If everything goes as planned, the next update will be for the first (rough) working prototype!

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    Build instructions coming soon!

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bdot wrote 03/26/2015 at 04:56 point

I have a feeling that a fast enough pull would either rip the string out of the box, break it or break the box itself.

But I do applaude you for trying to get some measurement devices into the gym

  Are you sure? yes | no

seminolemuscle wrote 03/26/2015 at 15:01 point

Thanks for the input. I dont think that's going to be a problem, since the string tension is a fraction of a lb. But in any case, the prototype you are referencing is one of many and the final design will be cardboard-free.

  Are you sure? yes | no

bdot wrote 06/05/2015 at 01:28 point

I can see why speed wouldn't be an issue, you're measuring powerlifters, not olympic weightlifters. 

I highly doubt it would survive a snatch from an efficient lifter.

I definitely like the updated design. 

  Are you sure? yes | no

seminolemuscle wrote 06/05/2015 at 02:14 point

Thanks! We've done olympic lifts with this with no issue. If you imaging pulling on a tape measure, it doesn't matter how fast you pull you won't create nearly enough tension in the string to cause a considerable amount of upward force. I can do the calculations, but i'm sure the acceleration would be way beyond what is humanly possible.

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Androiders wrote 03/13/2015 at 08:47 point

Cool project! I am interested in Olympic Lifting and crossfit myself. I had an idea to use an accelerometer attached to a barbel to record its trajectory to some computer. Never got around to it though.

But this velocity based training sounds cool. Must look it up,. any references?

Nice work so far! :)

  Are you sure? yes | no

seminolemuscle wrote 03/26/2015 at 03:40 point

Thanks! There's a product out there called "Push" Strength that has a lot of resources on its website for velocity based training.  There is also some research by Dr. Mike Zourdos that should either be out now or coming out soon, validating the RPE scale against velocity measurements. A lot of big name lifters use VBT, Mike Tuscherer and Chris Duffin to name a couple. They both have resources on youtube or their personal websites dedicated to it. That should get you started!

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