Push Car

I have had an idea to make a pedal car for around 4 years now(!) and I have finally got around to building one.(Well, almost, I had some problems so it's a push car now)

So I used Sketchup to design my car. It's loosely based on an MG J2.

So my major problem is the wheels. The car is being built for a 4 year old to drive so after the design the wheels come in at around 30cm (12 inches) in diameter. I tried to source a wheels for the project. I tried to get hold of a small kids bike, but there weren't any locally within the price range (I budgeted $40 for 4 wheels), ordering some from China (through Alibaba.com) was made prohibitively expensive because of the shipping ($25 for the wheel and $90 for the shipping was the quote I got) and then I discovered prams.

PRAM 1:

I managed to source a Valco Matrix 3-wheel-pram (broken) ($1 on eBay).

Now there are a couple of good things about these three wheeled prams that make them useful for this project.

Firstly the wheels come off easily. For this pram, if you push in the center of the rear wheels it releases a spring mechanism and the wheel pops off. For the front wheel, this pram has a quick release like a bicycle wheel.

The rear wheels are the really useful ones, for a number of reasons. The whole rear wheel section is removable so I can get the whole rear axle unit off in one piece. This give me not only the wheels, but custom made axles and the potential to do a bit of chopping and fitting and have my front and rear wheel mounts as well.

PRAM 2:

I bought a Swallow Beema Q pram also for $1 on ebay.

The wheels from this pram are for the rear of the vehicle. These wheels differ in two significant ways to the Valco wheels. (1) The axle is a little thicker, around 13mm as opposed to 10mm (2) The axle for these wheels is fixed to the wheel itself and the axle stub fixes to the frame - this is the reverse of the Valco wheels, where the wheel held to the axle which was off the frame.

Basically it means that for the wheels from Pram 2 different design methods will need to be used to attach them to the vehicle.

Materials:

600mm x 900mm plywood panels

Print outs of design.

Spray Adhesive.

Taking the shell off the design I am left with the frame. In order to get this is a useable form for cutting out I rotated all the pieces to lay them flat and within the bound of a 600mm x 900mm piece of paper (actually 590mm x 890mm because you need to allow a little bit of space on the edges in case the panel is slightly small - mine was short 5mm in both directions).

Now I wrote my own plugin for Sketchup which generates a .ps file for all the layouts and I can them convert this to a .pdf file for printing.

The print outs for this design I set to be A0 paper (841mm x 1189mm).

Firstly I printed out the sheets spread across A3 paper with edge overlaps to stick the pieces down like a jigsaw. An hour and half later I threw that idea in, no matter how I try I cannot get all the pieces to line up properly. So I needed another solution and I found one. I discovered the local print shop does basic A0 prints for $4 each, so I went there and had the plans printed out on one piece on paper.

I then took this paper, cut out the plans and stuck them down on my ply wood, ready for cutting.

To stick the paper to the wood I used spray adhesive.

To cut out the frame I used my scroll saw. Firstly I cut up all the pieces roughly (to make each one easier to handle), then used some sticky tape around the edges of the paper pieces (as the the glue was coming a bit loose in some areas) and then cut each of these pieces out more slowly and carefully along the edges of my layout.

It was during this process that I discovered that the plywood had split for two of the pieces of the cutout. Luckily I had a small piece of plywood left from a previous project that adequately fit the two pieces.

At the end I had whole heap of wooden cut outs for the frame that slotted together.

Having done most of the work on the frame I wanted to have a look at how things were progressing so I put it together.

This was mostly a slot together job (and therefore fairly quick). I did not fix the pieces in place (so they could be disassembled later)

I did have to sand/file to widen some of the joints a fraction to make it slot together nicely but this didn't take very long.

For the main frame I stuck the three of the four base pieces down using PVA glue and then nailed them into place the next day. It would have been too hard to make everything balance nicely otherwise.

Some of the longer pieces of plywood that I needed to stick to chassis frame had warped a little and so needed heavy weights/clamps to hold them in place while the glue set.

Having completed the majority of the frame, it was now time to tackle the front wheels.

Remember Pram 1 from earlier? Well, this is where it comes into the build. The plan was to turn the back wheels of the pram into the front wheels of the pedal car.

To do this I needed a number of things:

2 x rear wheels and fittings from the pram

2 x 15mm Pipe Tees

4 x 15mm to 10mm Pipe adapters

2 x 1/2 inch nuts (because the inner diameter of the threads is a tiny bit bigger than 10mm)

3mm drill bit

10mm drill bit

drill press

The pram rear wheel adapter is the key to make this step not too challenging. This is because it supplies a solid metal rod with a custom made groove in it to attach the wheel.

To build the fitting for the front wheel I had to drill a pilot hole across the pipe-tees, then enlarge these to 10mm (being the diameter of the solid metal axle. Once this was done I was able to remove the axles from the pram rear fitting by simply pulling off one of the washers and sliding it out the other side. I then inserted this rod through the hole in the pipe-tee and fitted the washer back on the other side.

Now, the width of the pram rear fitting was 36.4mm and the width of my pipe is 24.8mm, so I needed to add around 12mm worth of buffering to the metal bar to ensure that the pipe and original fitting were the same width to ensure a tight fit for the wheels. I used 1/2 inch nuts as the buffer because the inner diameter of space between the threads is a touch over 10mm and the width of the nut was around 11mm.

Once this was done I simply screwed in the 15mm-10mm pipe adapters to both end of the pipe-tees, ensuring the the length between the outside of the joints in the middle of these adapters was a 70mm (being the height of the chassis main frame) See diagram for see what I mean by this visually.

Now that the adapters were built I was (finally) able to put together the cross beam supports for the front wheels.

These were made from 19mm pine. Once I worked out the right length so the wheels would be far enough out from the chassis to give a decent turning circle, I cut the pine to length, drilled a 16mm hole and then slowly sanded this hole to make it just big enough so the end of the wheel adapters would fit in and turn smoothly without catching or squeaking.

Once this was completed, I put the front wheels together to check it all worked.

It did, so I attached the cross beams to the chassis (I screwed these in as though I am pretty sure the metal won't wear the wood too much or too quickly, I want to be bale to remove them and replace in future if need be).

I then attached the wheels (temporarily) to see how it looked together. Here I discovered that one of the sides did squeak a little, but tightening the pipe fitting a fraction removed this problem.

Now to attach the rear wheels.

For this set I had to make some extra pieces to add to the frame. This is because the vehicle chassis is constructed to taper inwards towards the front. I did this so I would have a bit more steerage at the front when completed.

To achieve this I cut out two angled pieces which I centered, glued and finally drilled into the rear of the frame. These were shaped so that the wheels (which are to slot into them) would have their axles parallel and lined up.

Once these were in position and bolted, I proceed to drill a 12mm hole through either side after careful measuring. This completed, I needed to get out a small file and work the insides of the axle holes until they were large enough to easily house a 1/2 inch axles (12.7mm).

This completed, I could finally pop all the wheels on and have a look.

Now for one of the more difficult steps of the build. In fact, I spent a lot of time on it... and all for nothing.

A couple of things happened here.

I measured out the distance between the axles and built a wooden crankshaft using copper pipe fittings as the corners.

Looked good, felt strong.

Joining it the axles proved a slight problem, I needed a bit more axle access, so I cut out small section of the chassis to make a gap so I could make the crankshaft-axle linkage.

I attached it in place and started to turn it and it broke. Basically it may have being rigid, but the wood couldn't take the torsional (turning) strain and the fibers of the wood ripped apart as it twisted.

As part of this I has drilled a hole through one the wheels and secured it with a small bolt to lock the wheel to the axle, so it's turn would be locked to the axle rotation.

I then tried to make a similar crankshaft out of metal. I managed to bend a few pieces of pipe but had no success.

In the end, I have a metal shaft that holds both axles together and it rolls well.

I will have to find another drive mechanism.

After the struggle of the crankshaft I hoped this would be easier.

Supplies:

2 x 1/4 inch threaded rod.

1 x 20mm diameter, 30cm long galvanized pipe with threads at both ends

1 x bracket

Firstly, to make the connection at the king-pin for the front wheels. For this I used the galvanized pipe. At the shop there were all sorts of lengths, from 6cm to 1m. I went with the 30cm because I knew I would need a little bit, but not quite how much.

With the pipe, I screwed it into the king-pin assembly and then made it position at right angles to the front wheel cross beams. That is, Aligned it how it would be if the vehicle were traveling forwards in a straight line, with the pipe pointing at the rear of the vehicle. I then marked the pipe where it's length would line up withe top front wheel supports. (This is illustrated in the image of the king-pin with the white paper in it)

I then unscrewed the pipe and added about 4cm to this length and cut the pipe there.

I then progressively inserted the pipe, checked how much turn I got, shortened the pipe again (by a little) until I had as much turn as I wanted, while still leaving enough room to add a vertical shaft out of its end to to connect it to the steering wheel.

In the end, my length was about 2cm from the original line I drew.

Having cut my second pipe section using the first as a I guide I moved on.

I then drilled a 6mm hole (leaving about 5mm gap at the end of the pipe section) through the pipe fittings, and filed it out just a touch where needed so the 1/4 metal rod could slide right through and twist easily.

I then attached the pipe fitting back on the king pin and twisted them in. I used the 1/4 inch threaded rod as a lever to turn the fittings that last half turn so the holes I drilled were straight up and down.

The steering rods were next. For this I took the 1/4 inch threaded rods and bent them on one end, at right angles 10cm from each end. Do this slowly and a little at a time or they snap.

I then mounted them to the bracket that I bought (I choose one with holes already so it would be easier for me to get things aligned properly.

There was a big delay as I got busy with work for a while and was only able to do snippets so my log of the project became a little vague.

Anyway, I got a working design of the steering going and then cut out the side panels.

Now all the pieces were cut out it was time to take them all home, one at a time, on the bus.

Construction was really quick. It took about 3 days to put together with the help of my children.

Everything slotted together fairly well and there was lots of drilling and glueing to get it all to hold fast.

We went with a three colour scheme. Post box red, cream and umber.

There was one final alteration to the base model that took a couple of weeks to come up with.

Since the vehicle was no longer a pedal car, I was the engine and leaning over to push was a pain in the back - literally,

But i came up with a solution.

I took a broom handle an screwed an eye bolt into the end of it. At the rear of the vehicle I attached a U-bolt.I then got a padlock and locked the eyebolt and the U-bolt together to create a strong but flexible joint with a long handle that I can push.