YOU CAN TURN A CHEAP SPIN BIKE INTO A SMART TRAINER IN ABOUT AN HOUR
A 3D printed motor unit that turns your spin bike's resistance knob, so a cheap spin bike follows Zwift hills and holds ERG power.
by doudar
HomeHealth
Built withESP323D printing
- difficulty
- ●●●○○
- time
- an evening
- license
- GPL-2.0
- repo
- repo ACTIVE285 stars
●●●○○ · an evening · GPL-2.0 · 285 stars · repo ACTIVE
WHAT YOU’LL NEED
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COMPAREE VERDICT
SmartSpin2k does one thing: it turns the resistance knob on a spin bike so you do not have to. You print the case, gears and arm, fit an ESP32 board and a NEMA 17 stepper (the V3 version uses an integrated PCB), mount it to your bike and pair it with Zwift, TrainerRoad or similar over Bluetooth. When the road tilts in the app, the motor turns the knob. In ERG mode it holds you at a set wattage by adjusting resistance as you tire. It needs a power reading to work from: either a bike that reports watts over Bluetooth or a Bluetooth power meter such as pedals (a heart-rate-based estimate is experimental). The repository and wiki are complete: printable parts, board files, a sourcing guide, firmware and a build PDF, and the parts come to under 100 dollars by the project's estimate. Community help runs through a Facebook group, and pre-assembled kits are sold at smartspin2k.com. The build is not complex, but it is fiddly — the knob coupling has to grip without slipping, and bikes differ, so check the bike-specific mounts and inserts first. The one thing most likely to go wrong is mechanical fit on your bike's knob. The creator's pitch: turn a 300-dollar spin bike into the equivalent of a 3,000-dollar smart bike. If you were planning to buy a bike anyway, a ready-made smart trainer will save you the weekend.
IN THE REPO
GOOD TO KNOW
- —Printable parts, board Gerbers, firmware and a full assembly PDF are all in the repository.
- —Hardware is under CERN-OHL-P-2.0, firmware under GPL-2.0 — both allow commercial use.
- —There is also a paid pre-assembled kit sold at smartspin2k.com, linked from the README; the open instructions let you source your own parts.
- —Calibration data is user-contributed and bike-specific — if your model is not listed, you calibrate it yourself against a known power meter.
- —The repository is active, last pushed in the past week, and the community answers questions in a Facebook group.
- —The project claims under an hour for the build; that is optimistic unless you have soldered ESP32 boards before and the printed parts fit your bike first try.
Parts to buy
6 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the Rev 3 building instructions PDF (in the SS2k-Hardware repository) and check the bike-specific mounts and knob inserts for your model.(If your knob is oval or recessed, you will need to adapt the printed coupler before ordering parts.)
- 2.Print the V3 case and the common assets from the SS2k-Hardware repository — arm, bike mount, 11T and 40T gears, knob cup, the insert for your bike, and the shifters.(The building instructions recommend ABS, ASA, PETG or PA for the whole design (40% infill, 4 walls, 0.3 mm layers), translucent PETG for the LED window and TPU for the shifters.)
- 3.Order the BOM from the hardware folder — ESP32, stepper, driver, power supply.(AliExpress links are provided but go stale; search by part number.)
- 4.Assemble the electronics (the V3 board and harness kit plugs together; self-sourced or V2 boards need soldering), flash the firmware, then mount and pair.(Follow the wiki's Loading Software page for the first flash; later updates install over the air or through the device's own web page.)
KNOWN ISSUES
- Not every resistance knob is covered. Browse the Inserts folder for an adapter that matches your knob, measure from the back of the head tube to the center of the knob (minus 65 mm gives the arm length) and check the arm table before ordering anything. If no insert fits, you will be designing one before you start.
- The stepper has to overcome your bike's resistance mechanism. Use the 38 mm NEMA 17 the sourcing guide specifies, and set the bike's minimum and maximum watts in the settings so it does not try to drive the knob past what the bike can absorb.
- Many spin bikes report inaccurate power. SmartSpin2k can correct it, and the wiki has settings pages for some bikes (such as the Schwinn IC4), but for others you need a reliable power meter to calibrate against, or ERG mode will not hold the wattage you think it is holding.
- The build time claim of under an hour assumes you have the parts, the prints are done, and nothing needs adjusting. First build with print time and troubleshooting is closer to a full evening, potentially two if the coupler does not fit.
- Pre-assembled kits are sold at smartspin2k.com, and the V3 build is designed around an integrated PCB you can buy as a kit or order yourself from the published files.
- Pairing order matters: the SmartSpin2k has to pair with your power source and then with your training app. Follow the wiki's pairing and troubleshooting pages, and ask in the project's Facebook group if you get stuck.
Will this work on my bike?
If your bike has a resistance knob that you turn by hand, probably. Check the Inserts folder for a knob adapter for your model and the arm-length table in the Arm readme; the V3 case needs at least 80 mm between the center of the knob and the head tube. If no insert fits your knob, you will need to design or adapt one.
Do I need to buy the kit or can I source parts myself?
You can source everything yourself. The BOM, printable parts and firmware are all in the repository. The kit shop sells a pre-assembled version but it is not required.
How accurate is the power reading?
SmartSpin2k does not measure power itself: it uses the watts your bike reports over Bluetooth or a Bluetooth power meter such as pedals, and it can adjust the bike's reported power if it is off. The creator notes many spin bikes have inaccurate power meters; a heart-rate-based estimate is available but experimental.
Does this work with Peloton bikes?
Yes. The V3 integrated PCB has a serial interface designed specifically for Peloton bikes, the firmware reads Peloton data directly, and the repository includes a Peloton mount and knob insert.
Community builds
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Discussion1
FROM THE COMPAREE TEAM
Around 285 stars, a companion app and a Facebook group — and the whole idea is not replacing a bike you already own. What resistance knob setup is stopping you?
doudar
doudar travels for work and started carrying power meter pedals to ride Zwift on hotel spin bikes, then built SmartSpin2k to add automatic resistance on the hills. The project now has a companion app, a Facebook community and pre-assembled kits for people who do not want to source parts.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM1mo agoedited
Practical notes from our verification: the firmware repository is under the doudar account and active, the hardware files and the Rev 3 building instructions PDF are in a separate repo (doudar/SS2k-Hardware) linked from the README, and there is a companion app for iOS and Android. Community help runs through a Facebook group linked at the top of the README. Pre-assembled kits are sold at smartspin2k.com if you do not want to print and solder. The single biggest variable is mechanical fit on your bike's resistance knob, so check the knob and the available mount files before printing. The project says the build can be done in under an hour; that is realistic only if the prints fit first time and you have soldered before. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.