THE SHOLLEY PROJECT
I have a shopping trolley. It is made in Germany and quite good, it has lasted me several years of weekly shopping trips during which I would push it to the mall and shop and then push it home full - and over that time I learned that there are problems with the design – and since I could, I started designing my own to replace it.
Original model weaknesses
Front wheels are too small. Even a small ditch can stop the cart.
Bendy. Some would call it a feature but the plastic frame bends a little on uneven ground. I want something a bit stronger. I am concerned that this will eventually result in it breaking.
Folding. The current model has a lot of complexity and parts because it folds flat while I don't need that. Yes, it is nice but unnecessary.
Low ground clearance. When I take it up steps the bottom gets scraped.
Basic Dimensions in cm:
length minus handle 64
width 54
height 84
ground clearance 8
main wheels 17
front wheels 9
upper bench height 57
handle overhang 23
Handle height 104
Bin internal 50 x 34 x 26
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DESIGN QUESTIONS
ONE: To fold or not to fold?
This is the big one: a solid frame is a lot simpler to make but not as useful.
I have designed a number of folding models but the existing model has almost never been folded. This, however, does not mean it will continue this way: I could in future move to a smaller place that makes folding necessary – but the complexity also brings weakness.
TWO: Stair Climbing
This means putting tri-wheels on the back - I would need to take these off an existing hand trolley. A useful feature as there are a lot of places where even a small step can cause a lot of trouble. The plastic trolley has its bottom gouged from these – the tri-wheels would not solve this but an aluminium frame will. Better ground clearance will help too.
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DESIGN VERSIONS
Version 10
This is based on the mostly plastic folding trolley I already have.
Version 30
Trying to make the lower tray accessible I split the tray. Not bad but I would need to find or probably make the split trays, not easy.
Version 40
Shifted the main wheels back to allow sliding the lower tray out sideways . This not ideal engineering wise however.
Version 63
This is the peak of folding designs – I even worked out a locking system for the front and back verticals. The down side? First, the complexity, second, the bottom tray has no protection against getting hit upward on bumps or steps. This was directly because I was trying to make it fold small and keep it light.
Version 67
At this point I was still thinking of folding it up and loading on the back of my bike so I put the folded design onto a virtual bike to see what it looked like and it looked bad. Clumsy and heavy.
From version 70 or so I decided to simplify and drop the folding aspect as it made things too complex. I also decided to add triwheels to make it easier to get up stairs and on and off public transport.
Version 74
The triwheels have arrived so here is the latest design with them as well as a solid (non-folding) frame.
This will make construction a lot easier and stronger but there is one down side: you can’t easily put brakes on triwheels. Still, this is looking the best yet. It is probably wildly overbuilt but as I don’t have FEA software I don’t care. It is made mostly of rectangle section alu with stainless steel bolts and nylock nuts. Brakes? Who needs them ! All of the parts are easily available and cheap enough - and now in my garage. all that I need do now is get time and space to actually put it together. Hopefully this will happen over the holidays.
