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YOU CAN TURN A CHEAP SPIN BIKE INTO A SMART TRAINER IN ABOUT AN HOUR

A 3D printed clamp that motorises your spin bike's resistance knob, turning a £200 bike into something that follows Zwift hills and holds ERG power.

by doudar

FULL CAD BOM FIRMWARE DOCS

HomeHealth

difficulty
●●●○○
time
an evening
license
GPL-2.0
repo
repo ACTIVE277 stars

WHAT YOU’LL NEED

  • 3D printer + filament — printable parts — files are in the repo
  • Electronic parts — full list with part numbers in the repo BOM
  • Dev board / microcontroller — runs the project firmware

Partner

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1

COMPAREE VERDICT

SmartSpin2k does one thing: it turns the resistance knob on a spin bike so you do not have to. You print a clamp, solder an ESP32 and stepper driver onto a small PCB, mount it to your bike frame and pair it to Zwift or TrainerRoad over Bluetooth. When the road tilts in the app, the motor turns the knob. When you are in ERG mode, it holds you at a set wattage by adjusting resistance continuously as you tire. It also lets you calibrate the power figure your bike reports, because cheap bikes with magnetic resistance often lie by 30% or more. The repository is complete: printable parts, board files, a BOM, firmware and an assembly PDF. The licences are permissive. The Discord is active. The build is not complex, but it is fiddly — the knob coupling has to grip without slipping, the stepper has to be strong enough for your bike's resistance spring, and if your bike model is not already calibrated by the community, you will need a separate power meter to do it yourself. The one thing most likely to go wrong is mechanical fit: not every resistance knob is round, and if yours is oval or recessed, you will be adapting parts before you ride. If you already own a spin bike and want it to follow virtual routes without buying a £900 smart trainer, this is the most proven open-source way to do it. If you were planning to buy a bike anyway, a second-hand smart trainer will save you the weekend.

NOT IN THE REPO

  • —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 kit shop run by the project; the page does not link to it and the instructions assume 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 Discord is still answering questions.
  • —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.

Can I build this?

PrintMain housing, knob coupler, motor mount and a small PCB enclosure — around 12 hours print time total on a standard FDM printer.
BuyESP32 dev board, stepper motor (NEMA 17 or similar), stepper driver (TMC2208 or A4988), small 12V power supply, assorted M3 hardware and a USB cable. The project BOM puts it around £50-70 if you source from AliExpress.
ToolsSoldering iron and solder, 3D printer, basic hand tools (screwdrivers, Allen keys), and a laptop to flash the firmware. You will also need a way to calibrate power if your bike model is not already in the community database — a second power meter or a friend with one.
SkillsBasic soldering (through-hole and a few header pins), 3D printing with support material, and enough comfort with a terminal to flash ESP32 firmware. No PCB design or C++ required — the firmware is pre-compiled. If you have built a 3D printer kit before, this is easier.
TimeThe project says under an hour. Realistic first build: 2-3 hours assembly, another hour for firmware and pairing, and potentially another evening if the knob coupling does not grip and you have to sand or reprint it.
Cost$$ — parts around £50-70, dominated by the stepper motor and ESP32. The 3D prints are cheap. If you already have a spare ESP32 and stepper from another project, closer to £30.
Safety12V DC only, no mains voltage in the device itself. The power supply is a wall adapter. The stepper motor can pinch fingers if you reach into the mechanism while it is running — mount it where you will not brush it mid-ride. No other real hazards.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Gallery

https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k
https://github.com/doudar/SmartSpin2k

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the assembly PDF in the docs folder to see if your bike's resistance knob will fit the standard coupler.(If your knob is oval or recessed, you will need to adapt the printed coupler before ordering parts.)
  2. 2.Print the parts from the STL folder — main housing, knob coupler, motor mount.(PETG or ABS recommended for the motor mount; PLA works for the rest.)
  3. 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. 4.Solder the PCB following the assembly guide, flash the firmware, then mount and pair.(Firmware flashing is via USB and the web-based ESPHome flasher — no command line required.)

KNOWN ISSUES

  • Not every resistance knob is round. If yours is oval, D-shaped or recessed into the bike frame, the standard coupler will not grip and you will be redesigning parts before you start. Measure the knob diameter and check the fit notes in the assembly PDF before ordering anything.
  • The stepper motor has to overcome the spring tension in your bike's resistance mechanism. If you buy a weak motor (holding torque under 4 kg·cm), it will skip steps on high resistance. The BOM specifies NEMA 17 with at least 4.5 kg·cm.
  • Calibration data is crowd-sourced. If your bike model is not in the community list, the power readings will be uncalibrated until you test it against a known power meter. Cheap spin bikes can be off by 30-50%, so 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.
  • The project repository is active but the paid kit shop (smartspin2k.com) is the main revenue source. The open-source instructions are complete, but some of the newer features and calibration profiles appear in the shop version first. Everything you need is in the repo; just know that the kit exists and some users will reference it in forums.
  • If you are using Zwift on iOS, the Bluetooth pairing can be flaky depending on your iPad model and how many other devices are connected. The Discord has workarounds but it is the single most common setup issue.

Will this work on my bike?

If your bike has a round resistance knob that you turn by hand, probably. If the knob is electronic, magnetic-only with no knob, or recessed into the frame, you will need to adapt the design. The assembly PDF has a fit guide.

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?

Only as accurate as your bike's internal power calculation, unless you calibrate it. Cheap spin bikes often overreport by 30% or more. SmartSpin2k lets you apply a calibration curve, but you need a separate power meter to generate it.

Does this work with Peloton bikes?

No. Peloton bikes do not have a manual resistance knob — the resistance is controlled electronically and the protocol is proprietary.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

287 stars, a Discord that still answers questions, and the whole thing is about not replacing a bike you already own. What resistance knob shape is stopping you?

CompareeTEAM13d ago

Practical notes from our verification: the repository is under the doudar account and active as of last week, the hardware moved to a separate repo (doudar/SS2k-Hardware) for Gerbers and is linked from the main README, and there is no official YouTube channel — the walkthroughs are community-made. The single biggest variable is mechanical fit: measure your resistance knob diameter before printing, because an oval or recessed knob will cost you an evening of CAD. The project claims under an hour for assembly; that is realistic only if the prints fit first try and you have soldered ESP32 boards before. Budget two evenings for a first build.

doudar

Created SmartSpin2k to retrofit an existing spin bike rather than replace it, then open-sourced the design when others wanted to build it. The project now has a community Discord and a paid kit option for people who do not want to source parts.

GitHub

Star the project on GitHub

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