Miniature belt drive

These days I have been working on the designing the final drive assembly for the custom chopper scale model. Initially I planned to use a miniature chain drive, by using a kit from Top Studio (see details in an older post). But while working on Tamiya's Yamaha Roadstar kit, I found out that you can buy miniature belts in various sizes, the smallest one being 3 mm width with 1 mm pitch. They are designed mainly for robotics but would look good on the scale models as well. Check out at SDP-SI for their belts offering.

So with this idea in mind, I changed the CAD project to use a belt final drive. I am going to use the 3 mm width x 1 mm pitch belt and will design the pulleys so the belt length matches the models sold by SDP-SI.

One issue that surfaced when I added the belt and pulleys in the assembly was the clearance between frame and tire; the belt and pulley was rubbing both the frame and tire. I had to widen the frame rear to accommodate the new final drive assembly. It doesn't look so sleek as before but is not bad either. The rear fender will have a cut-off for clearing the belt, but I will not model it in Inventor.

One of the advantages of designing the scale model in a CAD software is that you can find such problems early. When working with metal you need to be precise because unlike plastic, once a part is cut it cannot be adjusted too much.

Brake disks for the Yamaha Roadstar project - Part 2

Finally, the brake disks for the Roadstar are completed. It took me two attempts to do them, since I broke a 0.6 mm drill in and couldn't get it out, so I had to scrap the part and start again. The process of making them was as following:

• Installed some aluminum bar stock on the lathe and turned down few mm, to get to the 25 mm required diameter. The plan was to make both disks at once, so I took into account the desired brake disk's and the cut-off blade's thickness
• After that I removed the chuck from the lathe, with the bar stock still in, and mounted it on the rotary table, on the mill. Careful adjustments have to be made to align the spindle to the center of the brake disk. Then I started drilling the holes. I chose a simple pattern only with holes, in order to make it easier to fabricate. Basically there are five 4 mm radial holes, one 4 mm center hole (for the hub), five 0.5 mm radial holes for the bolts and forty-eight 0.6 mm cooling holes. Drilling the micro holes is tricky as the drills can easily break (which happened once) so I had to take my time. Also to make both disks at once, I had to drill deeper holes (around 2-3 mm), which is not really possible with such small drills (they snap easily). So in the end I had to do the disks separately
• After the holes were drilled, I mounted the chuck back on the lathe and cut a 0.8 mm "slice" from the bar. The 0.1 mm extra is needed for the finishing job, since the cut-off will leave a rough surface
• I then mounted the disk on the Dremel and polished the disk with 180 grit sandpaper, reducing the thickness to 0.7 mm

The disks should attach to the wheel hubs with 0.5 mm micro bolts; I intend to buy some from Scale Hardware.

All in all I am content how they turned out. Some photos below.

Brake disks for the Yamaha Roadstar project

I spent most of the past month designing a custom rear view mirror for my real motorcycle. Unfortunately I realized that the parts would be too big for the footprint of my Sherline mill so I put that project aside.

Now I am back to the Yamaha Roadstar project bike I introduced on the last post. Last evening I have started to turn the brake disks. Unlike the real bike, which has two front disks, mine will have only one upfront and one on the rear and it should look like this.

It has 25 mm in diameter (the same as the part in the kit) and 0.5 mm thickness (the kit part has 0.8 mm but looks too thick to me). It will be turned in 6061 aluminum. As you see, the patterns require drilling a lot of holes of various diameters. I am trying to make both disks at the same time and then just cut each one, like a slice of bread :) Might not work though as the tiniest holes are only 0.5 mm and cannot go deep enough (around 2 mm).

Below the stock aluminum bar reduced to 25 mm on the mill. All there is left is to drill the cooling holes, a lot of them...

Another side project

Today, I would like to show you another project I've been working for some time. It is based on 1/12th scale Yamaha Road Star 1600 kit from Tamiya.

The plan is to slam the rear and make add custom wheels and brake discs. I already made the wheels in 6061 aluminum and they are inspired by Harley's Fatboy ones. Think they turned out pretty cool and hopefully they will look even better once I will polish them.

In order to slam the rear I had to make a longer rear shock. I reused some plastic parts from the kit part but had to make most of the parts in metal (aluminum, brass and stainless).

Back to work

Now that I am back from vacation I continued working on the miniature tube bending device. To remind you, this is the device I will be use to bend the brass tubing for the bike's frame (3 mm) and exhaust (4 mm).

Parts are from aluminum and brass. Below a couple of pictures.

Summer break

For the last two months I have been in business trips and in between had the summer vacation. Haven't had the time to work on the project but I will be back at the beginning of September.

Enjoy the summer holidays.

Chopper Renderings

Yesterday, I did some refinements of the fuel tank shape and tried my hand on rendering the bike. Didn't have the patience to setup the lighting, just wanted to get it done fast.

Some updates

Due to a long business trip, the progress on the bike was slow. But since the last update I still managed to design the front brake caliper, headlight, handlebars and the fuel tank.

Thinking how I will make these parts, I suppose the tank can be made easier with modeling putty or even 3D printing, the headlight on the lathe (or use the plastic part from a Revell kit) and brake caliper again using 3D printing.

Still have to design the mounts for the fuel tank and the gas cap.

Rolling Chassis and bending miniature tubes

Today I am going back in time with the chopper project and I want to show you the 3D model of the rolling chassis and share some thoughts about the fabrication process of the frame.

As you can see in the photos, the rolling chassis is almost ready from design point of view. The remaining things to add is the top motor mount, the forward control mounts and rear brake mounts. The fender was redesigned in Inventor and now it includes mount holes to attach it to the frame. The fender clears the rear wheel at 1 mm and I am planning to use 0.5 x2 mm miniature hex bolts from Scale Hardware to attach it to the frame. The bolt head is only 0.46 mm in height so it should clear the wheel.

Back to the frame, it will be made mainly in 3 mm brass tube and the sections will be silver soldered together. All the bends have a 10 mm radius and to bend the tubes I started building a miniature tube bender. Fortunately, I found a nice CAD plan on the internet and only had to adjust the dimensions, use nuts & bolts I have around and remove some parts that I feel I don't need.

With the Inventor parts exported to CAD format, I went to a local water jet cutting workshop and they cut the basic shapes in no time (it took them 7 mins to cut all the parts). Unfortunately I found that due to the small dimension of the parts, the accuracy of the cut pieces is not that good. The water jet leaves a rough and uneven edge, which has to be milled or filed flat. This will reduce the dimension of the finished part with about 0.2 - 0.3 mm on each edge. So I had to enter the new dimensions in the Inventor solid model to get the actual size. So do take into account this aspect if you plan to use water jet cutting on small parts - you may need to rescale the parts a bit. However, the benefit in time is worth it.

Now it's time to finish the parts...

Chain drive design

It's time for the final drive design. For this project, I decided to use a roller chain instead of the "traditional" belt drive. I intend to use a 1/12 scale chain & sprockets kit from Top Studio, even though they are designed for Moto GP bike kits from Tamiya or Fujimi. But before ordering such a kit I need to design a sort of a mock chain and sprockets, just to assess the frame width and wheel/fender clearances.

After few days of gathering information and learning about chains mathematics (e.g. calculate the number of teeths, sprocket diameters), I finally managed to finalize the design and dimensions. I don't intend to have accurate sprocket ratio or pitch, just to have something to help getting the clearances right.

Just to give you an idea of the scale, here are the chain and sprockets data I came up with:
Pitch = 0.955 mm
Roller diameter = 0.5 mm
Roller width = 0.6 mm
Sprockets thickness = 0.5 mm
Driver sprocket outside diameter = 6 mm
Number of teeth on the transmission side sprocket = 18
Driven sprocket outside diameter = 18.843 mm
Number of teeth on the wheel side sprocket = 60

Of course these will change once I get the Top Studio chain kit, but it was a good learning exercise on how to design a chain and sprockets in Inventor. Plus that due to this exercise I discovered that the primary transmission plate has to be adjusted a bit to clear the chain. Also the oil tank's diameter had to be reduced from 13 mm to 12 mm, to clear the transmission plate. The rear fender will have a cut off on the left side, but I will not model that on the virtual model but do it directly on the fender part.

Later I will have to decide how to attach the sprocket on the transmission axle - I would like to be able to turn the rear wheel and both sprockets on the final/real scale model.

Here are some photos:

An introduction to the current project

The main project I am working currently is to design and build a 1/12 scale custom chopper motorcycle. I intend to build almost all the parts, with few exceptions being the tires, which are taken from a Revell motorcycle kit. The engine and gearbox will probably be 3D printed as is too intricate and complex to use conventional methods like milling. The 3D printed part will be used as a master pattern and they will be cast in resin. All the other parts will be made in metal, mainly brass and aluminum.

I have started this project approximately one year ago, working slowly on the design. Since it's an ambitious and complex project, I decided I will do the design in a CAD tool first and only then start building the physical parts. So I started learning various CAD tools and designing the bike in parallel. Actually the bike was the main motivator to learn the CAD tools as they are quite complex and have had no previous training in this domain.

Here are some photos of the current design

Welcome to my new blog

Welcome to my new blog, dedicated to scale model cars, motorcycles and connected hobbies. I started this blog so my hobbyist friends can follow my model builds easier.