Soap Box Build - Team Ecurious Ecosse

[Ferg]

There's not a huge amount of visibility of what people are doing for the Royal Deeside Speed Festival whether intentional or not. I'm not precious about designs or embarrassed about how bad some of what we might do might be ( the answer is quite bad ) or how many corners we cut ( plenty but none in the actual course) so I'm going to post up what we've been doing or not doing as is often the case.

This is the first soap box I've built with the intention of competing. I have a young keen driver of 8 years old who's going to pilot and approval from the Mrs so it's go for the project.

Design was of concern. I saw a basic design using bmx forks which allows incorporated brakes so decided that was the approach to take. After much sketching in napkins and the like the following is pretty much where I got to.



The design and parts acquisition stage or 'procrastination' stage has taken its time. So with only three weeks to go I thought we better get started.

On Monday I laid out the parts roughly where I wanted them to go.



An acquired school seat is the best scrounge but I gave up finding 4 matching wheels and admittedly bought new wheels. Very cheap they were.

[Ferg]

On Wednesday we actually got moving after some encouragement.

Kids looking much more helpful than they maybe were but all good fun.



The main issue with the BMX forks approach is the turning force around the head tube. Hence I've gone for an over engineered centre bar onto which they attach. That was completed Wednesdsy Morning. All going well.



And then in the afternoon making a load of mess...


We had the first pass at the chassis done. Nothing permenantly fixed just laid out but much better to see it materialise. Note the the 13Degree backward slant on the front so that caster angle is automatically added to the geometry at the front of the cart.


And because the kids always want to out the seat on it...



Next step is to get the cross member glued and drilled and attach the forks as I can't make a call on the king pin angle until I've done so. Going in the right direction so far though.

[Ferg]

So was going to glue and screw the rear today where I read the pack that came through from Tony. I'd made a mistake in the width and had thought the width was a guideline so had been building to Scottish cartie regulations. Instructions showed that there was a max width of 750mm. My chassis was 800 mm wide in order to meet the minimum track width of 700mm from the Scottish Cartie Association rules. Doh! Thankfully nothing was glued yet but I still damaged a fair bit and made poorer cuts in the adjustment. I also split some of the wood so strength now a concern.



Now a compliant 750mm wide.

[Corranga]

Looks like great fun,I love seeing something come together from plans to completion

[Kinger]

Looks brilliant Ferg,

Looking forward to seeing the build of the steering mechanism etc. Keep the posts coming

Now need to come along and see it in action on the big day

[C7Steve]

Steve.

[pete]

That's literally the best thing I have seen today.

Wish i was entering.

[hendeg]

Love it

[Dominic]

Great effort! Nice design too

[campbell]

We are very impressed here. And now feeling the pressure =8-o

[mwmackenzie]

Great work Ferg! Looks great

[Ferg]

Got some time at it yesterday.

The BMX forks were meant to save time but securing them was a question.
I had wanted to do a saddle clamp originally but couldn't find something appropriate off the shelf. Not saying it's not out there and I may have been looking in the wrong place. So decision was made to bolt through the head tubes.

Problem is then that I was worried about compromising the strength of the tube and also squishing it inadvertently with the bolts. So we made some steel inserts for the tube. It will stop the squish and hopefully ( no actual proof though) this will prevent bending of the tube round the holes.



I didn't have a vertical drill big enough so had to drill the guide channels by eye. Result was mixed but once adjusted it holds the fork straight.





And today:

With the jumps on the course there is going to need to be some give somewhere. I got some door stops but they turned out to not be solid. Modern efficiency :rolleyes I've left them in for now but will find some bush rubber. I wasn't prepared to chop up the Elise roll at bushes I had in the garage.



Had an unexpected issue. The fork drop outs were too small for the 14mm axles. Some application of Dremmel later and they fit.
Rear module getting there.



And finally for today I affixed the main chassis legs. These go over the central section and in an effort to never look like it's under engineered, and more because the glue and screw didn't look sufficient for containing the force from the rear, I added a re enforcing plate of ply underneath.



Chassis coming together. Hopefully start on front assembly tomorrow.

[BigD]

Looks great Ferg. Good skills there.

[campbell]

No pics here yet but hopefully some tomorrow. Rear subframe assembly, steering axle design & build, and poss first rolling test tomorrow.

[Ferg]

So....steering.

The aim is to have a steering wheel type. This will need a column etc but the immediate challenge is sorting the front uprights. Having looked through various sources for geometry for carts I wanted to deliver as near as I could to a setup that follows convention. This basically means producing uprights that introduce appropriate king pin angle, castor and follow Ackerman geometry. I've built the castor into the chassis to simplify it. King pin angle is going to be rough as we're not designing this to a tight tolerance. But hopefully get approximately the right thing. Ackerman is more to do with steering actuation so we'll leave that till later.

I'm lucky to have access to a basic milling machine so with Assistance from my Dad as owner and operator of said machine, we thought we'd try and make something interesting to address the requirement. It's going to be basic but it's part of the fun. A full family effort.

Initial sketches again:


Getting more serious. Have small blocks of metal. Stuff gets expensive as it gets bigger so we're going to produce something with the smallest block we can.

Sketching out the wheel dimensions to find king pin angle. Neutral steering is exactly lined through the point of contact of the tyre. But most things I read suggested having the line a little inside the contact point to put some resistance into the steering.


Worth noting that most of this is just based on reading a few internet articles and then sketching out on scraps of paper. Not pretending to be knowledgeable in any of these areas. The Scottish Cartie Association website has provided most of the links for the geometry stuff.