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In Development

Sled.wtf

A regenerative exercise sled that captures your push energy, measures everything, and makes every workout count. Uphill both ways.

What is Sled.wtf?

Sled training is one of the most effective full-body conditioning tools available—low impact, high intensity, and incredibly versatile. Sled.wtf takes the classic prowler and transforms it into a sensing, regenerative machine.

Push the sled and spin an alternator through a two-stage pulley system. Adjust resistance from "Puppy" to "Monster" with a dial. Capture your energy into a battery. Track every metric—torque, RPM, power output, efficiency—in real time.

Key Features

Regenerative Power

A 130-amp alternator driven by a 23:1 two-stage pulley system converts your push energy into electricity, stored in a LiFePO4 battery via supercapacitor buffer.

Adjustable Resistance

ProFET-controlled field current lets you dial resistance from easy to brutal. Same sled works for your kid or an NFL linebacker.

Full Sensor Suite

Strain gauges for axle torque, Hall effect sensors on all 3 shafts for RPM and belt slippage, current sensors, thermistors, and LoRaWAN GPS.

The Tech Stack

Mechanical

  • 12" rear wheels on keyed 1" steel axle
  • Two-stage V-belt pulley system (23:1 ratio)
  • Jackshaft with 10.75" and 18.75" pulleys
  • Denso 130A alternator (salvaged from Lexus RX330)

Electrical

  • ProFET field driver for variable resistance
  • XS Power SB500-48 supercapacitor (4000W buffer)
  • LiFePO4 battery with Victron smart charger
  • Dump resistors + blower fan for excess energy

Sensors & Telemetry

  • ESP32-C3 microcontroller
  • Wheatstone bridge strain gauges (torque measurement)
  • Hall effect RPM sensors on all 3 shafts
  • INA219 field current sensor
  • Allegro ACS770 current sensors (alternator output, dump circuit)
  • NTC thermistors on dump resistors
  • LoRaWAN GPS tracker (Digital Matter Oyster2)

What It Knows

  • Torque — Real-time axle torque via strain gauge bridge
  • Speed — Precise speed from rear axle RPM
  • Power Output — Watts generated per push
  • Alternator Efficiency — Calculated from torque, RPM, and current
  • Belt Slippage — Detected by comparing shaft RPMs across stages
  • Thermal Status — Dump resistor temperature monitoring
  • Location — GPS via LoRaWAN (where's my sled?)

Follow the Build

The entire build is documented on the sled.wtf blog. Watch the design evolve, see the mistakes, and learn alongside the project.

Read the BlogContact Us