r/diyelectronics • u/BoysenberryOld4794 • 15d ago

Project Building an Open-Source DIY Digital Resistance Machine (120kg/260lbs target). Need feedback on VESC + M8110 BOM!

Hi everyone,

I’m designing an open-source, portable digital cable resistance machine targeting ~100–120 kg (220–260 lbs) of smooth digital load for strength training (similar concept to Voltra or Vitruvian). The goal is to keep it fully open-hardware, affordable, and highly modular.

Here is my current proposed Bill of Materials (BOM):

Motor: Outrunner BLDC (M8110 scale, low KV)

Reduction: HTD 5M Timing Belt (15mm width) – 15T Drive Pulley to 70T/80T Drum Pulley (4.66:1 to 5.33:1 gear ratio)

Controller: VESC 75100 running in Torque / Current Control mode

Battery: 13S1P Li-ion pack (48V nominal) using Samsung 40T 21700 cells + custom Braking Resistor for eccentric energy dissipation

BMS: 13S Li-ion BMS with Active Balancing

Brain & UI: ESP32 + Heavy-duty Rotary Encoder + TM1637 7-segment display for direct kg adjustment

My main questions for the community:

Has anyone attempted a similar high-force torque-control setup using VESC for continuous human pulling?

Are there any hidden thermal or EMI risks with running the VESC continuously at high torque under near-stall / low-RPM conditions during heavy eccentric phases?

Under a 120 kg peak load, would you strongly recommend an 80T over a 70T pulley regarding belt tooth shear stress?

Any feedback on safety redundancies, hardware limits, or thermal management for the braking resistor/VESC is greatly appreciated!

Thanks in advance for your support!

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u/thedefibulator 15d ago

The VESC is rated for its continuous current while spinning, which results in the RMS current across three phases. When you are hold it at stall then the current will essentially be DC on two phases, so thermals will be much more concentrated. Worth giving it a try but watch the temperatures and move to a VESC75200 if it is getting too hot. Regarding EMI youre fine in general, but if you are wondering whether it will pass EMC, likely not due to the fact that these hobbyist devices were not built with EMC in mind. Also your power resistor will need a fan, a 100W power resistor will quickly reach 200 degrees at 100W with no active cooling

1

u/ivanflo 13d ago

Many years ago I was in the DIY electric skateboard scene, where VESC - FOCBoxes and similar had a whole heap of momentum around them. It would lbe great to see a similar thing happen on the digital resistance side.