Volt-Crane-O

Volt-Crane-O
Built By	Chris Stubbs
Theme	Liebherr Mobile Crane
First Race	EMF 2024
Current Status	Active
Motor	6x Hoverboard 6.5″ Hub Motors
ESC	3x Hoverboard PCB
Battery	48V 12S3P Li-Ion/LiPo (2x 6S)
Transmission
Contact	@emfroamer
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Background

Volt-Crane-O is a scratch built, 6 wheel drive, 4 wheel steer, fully functional miniature crane.

The theme is based around a Liebherr 6 wheel mobile crane.

Construction

The chassis is constructed from wood, mostly 2x4. Fixings are mostly wood screws, except the use of M8 bolts where additional strength or rules compliance is needed.

The body is also constructed from a lightweight wooden frame, panelled with thin plywood.

Steering uses two M8 threaded tie rods to connect the pitman arm to the trailing spindle arms. The steering column is 25mm bed frame offcut with socket set articulating joint. There is a second pitman arm on the steering column at 90 degrees to produce a back and forth steering linkage to the rear axle, which is then translated 90 degrees again using a pivot to drive the rear tie rods. The steering angle of the rear axle is approximately 1/3rd of the front steering angle, because the rear/mid wheelbase is approximately 1/3 the front/mid wheelbase. No real thoughts were given to steering geometry and the handling is somehow "fine".

Powertrain

Volt-Crane-O utilises 6x 6.5″ 350W hoverboard motors, fitted with 4.10/3.50-5 tyres. Regenerative braking is extremely effective if configured correctly, however one motor has been fitted with a mechanical brake from a Xiaomi M365 scooter to comply with the rules.

Power is delivered to the motors using 3x original hoverboard PCBs running a fork of EFeru’s FOC firmware (links at the bottom). A higher current limit is applied to the rear motors to aid traction given the awful weight distribution. Throttle is applied in torque mode, controlled from aliexpress hall effect pedals via an Arduino.

Traction power is supplied by either 2x custom 6S3P Samsung 30T 21700 Li-Ion battery packs, producing 48V total. Each pack contains a 60A DALY BMS, or 2X 6S 9500mAH CHNL Lipos. Another 6S4P Li-Ion set using reclaimed hoverboard 18650’s also exists for testing and running around, but does not perform well enough for racing.

Other Features

A fold up trolley makes an effective trailer for running gear from the car park to the track!

(crane)

The Arduino logs all hoverboard and arduino telemetry locally via SD card.

Awards

• EMF 2024
  • 3rd place overall.
  • 1st place Moxie.

BOM

coming soon

Limitations

Steering wheel snapped off.

Sluggish on mud/grass.

Heavy (100kg).

Happily pops 30A fuse if accelerating too hard/long.

Resources

Twitter Account @EmfFRoamer

The Hoverboard firmware, Arduino code, and CAD on GitHub

Remote control Pi code on GitHub

Chris’ website

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