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YOU CAN RUN AN E-BIKE ON YOUR DRILL BATTERIES

Two Ryobi 40V drill batteries slide into 3D printed holders and power a 500 W mid-drive e-bike. The team estimates about 21 miles with pedal assist.

by Maya Roman, Peter DeNicola, John Rozzo and Nick Bohn

FULL CAD BOM FIRMWARE DOCS

AutomationWorkshop

Built with3D printing

difficulty
●●●●○
time
a weekend
license
CC-BY-NC-SA-4.0
repo
repo ACTIVE28 stars

WHAT YOU’LL NEED

Videos
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COMPAREE VERDICT

This is a university student project that puts power tool batteries on an e-bike. Two RYOBI 40V 4Ah packs give you 320 Wh, which the team calculated as about 21 miles with pedal assist or about 13 miles on throttle only, at 20 mph on flat ground. The batteries slide out, so they can go back to your tools. The written guide in the repo has a full parts list with 2021 prices, wire sizing, step-by-step instructions for the wiring harnesses and the install, plus Fusion 360 and STL files. The motor kit is not part of the guide. You buy a Bafang 500 W mid-drive kit and fit it to your bike yourself. The biggest catch is legal: 500 W is above the 250 W e-bike limit in the EU, so check your local laws before you ride. Money-wise, the 2021 parts list came to 759.25 dollars, with 404 dollars for the motor kit and 288 dollars for the two batteries. The bike was donated, so it is not in that total.

GOOD TO KNOW

  • —Fusion 360 files and STL files (thick and thin mount base, plus a lid) are in the repository, along with a critical dimensions drawing PDF.
  • —The written documentation PDF has a full parts list with 2021 prices: $759.25 total, $404 for the Bafang kit, $288 for two RYOBI 40V 4Ah batteries.
  • —The PDF has step-by-step instructions for the internal harness, the Y-harness and installing the mounts on the bike, plus a how-to video.
  • —The license is CC BY-NC-SA 4.0: you can share and adapt it, but not for commercial use.
  • —The repository was last updated in May 2021. It is a finished student project.
  • —You buy the Bafang mid-drive kit separately, and the donor bike is not in the parts list.

Parts to buy

11 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Bafang 500 W mid-drive kitFind
  • Two RYOBI 40V 4Ah batteriesFind
  • 12 AWG stranded wireFind
  • XT60 connectorsFind
  • Power timer contactsFind
  • M5 and 6-32 boltsFind
  • Heat-set insertsFind
  • Heat shrinkFind
  • SolderFind
  • PLA filamentFind
  • Donor bikeFind

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Can I build this?

PrintTwo mounts and two lids in PLA (the team used 20% infill and 0.2 mm layers on Ender 3 printers), about 59 m of filament
BuyBafang 500 W mid-drive kit, two RYOBI 40V 4Ah batteries, 12 AWG stranded wire, XT60 connectors, power timer contacts, M5 and 6-32 bolts, heat-set inserts, heat shrink, solder, PLA filament, and a donor bike
Tools3D printer, soldering iron (also used to set the threaded inserts), knife, pliers, heat shrink, tools to install the motor kit, and Fusion 360 if you change the design
Skills3D printing, soldering and wiring, fitting a mid-drive motor kit to a bike, and checking your local e-bike rules
TimeA weekend: the team's goal was a conversion you can do within a weekend
Cost$$$: the 2021 parts list totalled $759.25, of which $404 was the Bafang kit and $288 the two batteries; the bike is not included
SafetyLithium-ion packs and a 25 A motor controller: use properly rated wire (the team used 12 AWG), get polarity right and avoid shorts, or wires can melt. 500 W is above the 250 W e-bike limit in the EU, so check your local laws before riding. License is CC BY-NC-SA 4.0, non-commercial only.

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

Videos

DIY EBike Battery System6:50

The team's how-to video, posted May 2021 on Maya Roman's channel: how they made the battery system with 3D printed parts and two RYOBI 40V batteries.

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Gallery

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 written documentation PDF in the repository (Parts list, range math, wire sizing, and step-by-step harness and install instructions)
  2. 2.Watch the how-to video (Shows how the team built the mount and wiring)
  3. 3.Check e-bike laws where you live(500 W is above the EU 250 W e-bike limit; check local rules before you buy parts)
  4. 4.Check your bike(Water bottle bosses for each battery, ideally disc brakes front and rear, and a bottom bracket that fits the mid-drive kit)
  5. 5.Print the mounts and test-fit a battery (The team printed in PLA at 20% infill and 0.2 mm layers; the repo has a thick and a thin base, plus a lid)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • Check the law first. 500 W is above the 250 W e-bike limit in the EU, and the team tells you to check your local, state and federal laws before riding a self-made e-bike.
  • All prices are from 2021: $759.25 total, $404 for the Bafang kit and $144 per RYOBI battery at the time. Today's prices may differ, and the bike itself is not included.
  • This is a battery mount, not a full e-bike kit. The guide covers the mount, the wiring harnesses and installing the batteries, but you install the Bafang mid-drive kit yourself.
  • Your bike needs water bottle bosses, one set per battery. The team also recommends disc brakes front and rear, and you should check that your bottom bracket fits the mid-drive kit.
  • Wiring matters. The motor controller is rated for up to 25 A, so the team used 12 AWG wire. Loose connections, too much current or a short circuit can melt wires. Get the polarity of every XT60 connector right.
  • The range numbers are the team's math at 20 mph on flat ground. Your weight, wind, hills and road surface will change them.

Can I use a different brand of power tool battery?

The mount is designed for the RYOBI 40V battery. The team lists versions for other battery brands as a future idea, so for another brand you would need to change the battery mating shape in the Fusion 360 model yourself.

Is 500 W legal where I live?

It depends on where you live. In the EU the e-bike limit is 250 W, so this 500 W build is above it. The team also says to check your local, state and federal laws before riding. In their test the bike hit 24.8 mph on flat ground on motor power alone.

Which battery and how many?

The team used two RYOBI 40V 4Ah batteries wired in parallel with a Y-harness. Each set of water bottle bosses on your frame holds one battery, so for two batteries you want bosses on both the down tube and the seat tube.

What is the real range?

The team calculated 320 Wh total (40 V x 4 Ah x 2). At 20 mph on flat ground that is about 21.3 miles with pedal assist and about 12.8 miles on throttle only. They say to use this as a guide, not a promise. Weight, wind, hills and road surface change it.

Do I need the exact same parts as the team?

No. The team says the only part you should match exactly is the power timer contacts that touch the battery terminals. The other parts, including where you buy the motor kit, can be what you have or can find. Check that your bottom bracket fits a mid-drive kit.

Community builds

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Discussion1

FROM THE COMPAREE TEAM

The team calculated 320 Wh for about 21 miles with pedal assist. Have you run power tool batteries on an e-bike, and did your range match the math?

CompareeTEAM14h ago

Practical notes from our verification: the written guide in the repo is more complete than most student projects. It has the parts list with 2021 prices, the range math, wire sizing for the 25 A controller, and step-by-step instructions for both wiring harnesses and the install. What it does not cover is installing the Bafang motor kit, so plan for that separately. The repo has not changed since May 2021, which is normal for a finished student project. The license is CC BY-NC-SA 4.0, so personal builds are fine but selling it is not. Check your local e-bike laws first, because 500 W is above the EU 250 W limit.

Maya Roman, Peter DeNicola, John Rozzo and Nick Bohn

This was a Spring 2021 XProject at the University of Pittsburgh's Swanson School of Engineering, built by students Maya Roman, Peter DeNicola, John Rozzo and Nick Bohn. Their sponsor asked for a battery for DIY e-bikes that is cheaper than big proprietary packs and safer than cheap ones. Their answer was to use common power tool batteries that are easy to buy and replace. The bike was donated by Thick Bikes in Pittsburgh.

GitHub

Star the project on GitHub

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.
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