bighak

This is bighak

Due to a desire to go to Newcastle makerfaire, we at Hitchin Hackspace decided to get together and make something as a group. Whilst at the pub chatting things over we decided to build a full sized version of the beloved children's toy, the bigtrak.

An ambitious project, especially with the exhibition deadline being only 3 months away, things got off to a great start. Those that didn't help with the build helped with material sourcing. This way we managed to quickly procure 'honeycomb aluminium', 2 golf kart wheels, wood for bodywork and L-shape steel from an old greenhouse.

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  Happy Dave
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  Test Drive
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  Rob on caffine

Group Build Day

Using A0 plotters to print out 1:1 scale templates, cutting the aluminium sheets with jig-saws as a group cut the build time down significantly. After the first full build day, we quickly split into sub-groups to power through the workload quickly. Combined with the use of Trello to organise and report progress and weekly IRC meetings, the project continued well by working mostly evenings and weekends.

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  Group build day
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  Everyone working together
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  Putting it all together
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  Theres always one "manager"
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  Luke's exquisite cornering
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  Riveting
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  More riveting
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  Even more riveting
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  Axle alignment

Body Work

Attention to detail for the bodywork was paramount. From an early stage it was decided that it had to look good. Something that looked 'kinda like' the bigtrak just wouldn't do. A lot of car body filler was used here coupled with a lot of sanding to give each corner and curve the right effect. The finish was obtained with plastic paint. This would give the final surface it's shiny / glossy coat as well as make the thing look like a plastic toy, only bigger.

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  First nose draft
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  Nose connections
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  Aligning nose
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  Nose fitted
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  Side Pod
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  Sighting Side Pods
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  Test assemble looking at gaps
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  Test assemble looking at wheel positions
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  Nose cone with 'lots' of filler

Chassis and Axles

If the bodywork had to look good, the chassis had to be perfect! Honeycomb aluminium is very strong and light, but as with anything, there is a compromise. It is very susceptible to point loads and de-lamination. Several different styles of joints were tested to make sure we do it right. The biggest fear was structural failure. We had just enough aluminium for one unit. If anything broke, there were no replacement parts available without heavy cost and delay. Being unfamiliar with the material, Luke Clampitts advice and assistance was invaluable in getting the project finished on time and to a high enough quality.

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  Chassis taking shape
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  Use of cardboard templates
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  Centre strut from template
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  Chassis with wheels
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  Motor Axle Bearings
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  Front axle choices

Sanding and Painting

With time at a premium, a lot of elbow grease went into the filling, sanding and painting of the tub and bodywork. As with all the best OCD workers, the sanding team still want to fill and smooth down the surface at least one more time! There were many complex curves on the nose cone as well as the side pods. After the first coat of spray paint the bighak really started to look the part, so much so that everyone was extremely proud of the work done.

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Other Parts

It's always interesting to see where we got some of the components for this build. Here you can see we bought the jeep for it's wheels. The jeep was dismantled to see if any part of it could be re-used. bighak's power comes from two paired wheel chair motors. They came with a motor controller and joystick which is going to be 'hacked' to allow computer control to mimik the keypad control of the original bigtrak.

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  Toy jeep
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  Ripping the jeep apart
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  Wheel chair motors