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Stuff and Things

Printing big with carbon fibre-reinforced nylon and PETG, Robox 3D printers with the Olsson Ruby nozzle are helping a leading materials handling equipment manufacturer stay ahead of the competition

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“Big Dave and his little brother make parts in days that would otherwise take weeks or even months to prototype or manufacture conventionally. With cost savings of over £40k achieved in the last year alone, our Robox 3D printers have become an integral part of our business and we’re pleased to call CEL our partners.”
BIL Group Ltd

Our RoboxPRO and RoboxDual 3D printers, “Big Dave” and “Little Dave”, have enabled us to make durable, accurate and cost-effective prototypes quickly with a number of design iterations we simply couldn’t achieve with traditional processes.

Tim Murrow commented: "As a leading manufacturer of castors, wheels and materials handling equipment, being able to create high quality prototype parts and tooling quickly is essential in helping us win business and stay one step ahead of our competitors."

With the new SingleX head, we are now able to use engineering materials such as nylon infused with carbon fibre. The Olsson Ruby nozzle included in the head is incredibly hard-wearing and works with the toughest, most abrasive materials. Using RoboxPRO, we can now produce very large, robust parts that look great and are suitable for trialling on real sack trucks in the field.

Matt Walker added: "We considered other 3D printers but settled on RoboxPRO as it not only meets our demanding needs at an affordable price, but also comes with fantastic support. The technical support team at CEL are friendly and always happy to help us get the most of our 3D printers."

Big Dave and his little brother make parts in days that would otherwise take weeks or even months to prototype or manufacture conventionally. With cost savings of over £40k achieved in the last year alone, our Robox 3D printers have become an integral part of our business and we’re pleased to call CEL our partners.

BIL Group are suppliers to major UK supermarket chains, motor manufacturing plants, airports, MOD, supply chain logistics and many more. Contact us for more information on our leading castors, wheels and materials handling equipment.

Web: www.bilgroup.co.uk
Tel: +44 (0) 1249 822 222

BIL Group Ltd

Dieselpunk Crawler, Part 2

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After getting off to a rapid start my Dieselpunk inspired crawler ground to a standstill while I waited for parts, now that they have arrived everything is up and running. Sometimes when the design and printing go well they are the quickest part of the project!

All of the parts fit in the RoboxDual, you can find them here for download. I printed the vast majority of the project in ABS, but PETG will do just as well.

Since sculpting is not my strong suite I called in the assistance of my talented friend Fotis Mint who was kind enough to model a cool head for the driver. There is nothing quite like 3D printing and the internet to make a collaboration across thousands of miles seem like you are working in the same studio.

The torso and all of the joints were modeled in Fusion360 after which I sent the torso and neck piece to Fotis Mint who sculpted on those in ZBrush.

From the perspective of design for printing however the most interesting part of the project are probably the various arm joints on the driver figure.  I needed a lot of freedom of movement, so that the steering wheel servo could make the arms move, without putting much strain on it. I also wanted to avoid fiddly assembly and printing with supports, so I came up with a three piece design that results in 5 axes of movement. Two of the joints are simple pivots using 1.75mm filament off-cuts as hings, but the others print in place, as shown below. These are the sorts of things that would be impossible to do with other manufacturing methods.

The assembly of these joints can be seen at the 7 minute mark of the video below.

 

 

 

Dieselpunk Crawler, Part 1

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One of the best things about 3D printing is that it lets me work fast enough that I can get an impulse project from concept to reality before I lose the inspiration.

I have had the idea to build a small tracked RC vehicle for ages, but when I came across the Tiny Trak it just wouldn’t get out of my head.

Usually when an idea gets stuck in my head I am forced to scribble it in my notebook to make it go away, but this time that didn’t work and the sketch quickly turned into a CAD model and two weeks later was a printed design sitting on my desk.

This little beastie is 200mm long, powered by two continuous rotation servos, and will have an FPV camera in place of the driver’s head, allowing us to pilot it from the driver’s seat. I’ve designed it to be easy to print and assemble and its small size and low price should make for a fun weekend project.

The project is now waiting on some electronics, and a design for the driver, stay tuned for updates, and files once they are tested!

Ossum Racer, Part 4: Rear Axle Continued

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In the last post we got a working differential together, since then I have been designing the axle tubes, axle shafts and the drive shaft.

Axle Tubes

I have mentioned from the beginning that I am trying to keep the complex mechanical components compatible in size with off-the-shelf RC components, so I have made the width of the axle and the mounting points exactly the same as the Boom Racing SCX10 axle that I used on my rat rod build.

Printable rear axle with differential compared to Boom Racing SCX10 axle for size

The housing of the differential has been redesigned so that all of the tolerances are contained within one part, and the cover simply screws down on top, holding the two largest bearings in place. Nothing has an overhang more than 45 degrees, so it is all printable without support.

Inside the axle tubes there are two bearings which support the printable axles shafts. The axles shafts have provision for an M4 rod down the middle, which provides both strength and the opportunity to use standard RC wheels if desired.

Printed Prototypes

I printed and assembled prototypes based on this design and it went together well. My plans to test immediately were delayed due to some mistakes I made in the sizing of my driveshaft, but the assembly feels satisfactory when turned by hand, I have high hopes for the first test!

The assembly, printed in ABS filament

Next Step

Stay tuned for the assembly and test video of the rest of the axle shortly, as well as work on the drive shaft and universal joints.

Ossum Racer, Part 3: Designing the Rear Differential

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Over the past few weeks, with a brief hiatus due to international travel for my day job (I’m an Electrical Engineer in the telecoms industry), I have been plugging away at the design of the rear differential.

I have a few design goals for the rear axle

  • Approximately the same size as a “standard” 1:10 crawler axle (both to make this re-usable in other applications and to make it possible to use a commercial axle on this build)
  • Functional open differential
  • Accept standard RC wheels with a 12mm hex drive
  • Rugged enough gears to handle, at least, a “silver can” 540 motor
  • Look fairly realistic (not too important in this build since it will probably be hidden)
  • Preferably printable without support

Of course the rear axle can be made significantly smaller (or stronger, in the same envelope) if we go from a open differential to a spool, which will be a suitable modification if it is to be used on a rock crawler.

Design Approach

I first attempted to design from the outside inwards, starting with my goal diameter for the differential and designing gears to fit inside it. This turned out to be a bad idea, causing endless redesign, it was much more sensible to design the gears and build the casing around it.

There are other aspects to keep in mind, almost all of them relating to tolerances. For example, if a bearing recess is part of the face that contacts the printer bed then the slight bulging can prevent the bearings from fitting.

Designing Bevel Gears

Unfortunately Fusion360 doesn’t have a decent tool to create parametric bevel gears and designing them properly yourself is no mean feat. This is a real nuisance because we have to import gears from elsewhere and then design around them.

Fortunately there is a very nice script written for OnShape which you can find here and it is not too much trouble to set them up as you like, export as STEP files and import into Fusion360.

In order to keep my design “semi parametric” I positioned all of the gears sensibly with respect to the origin, and then defined variables which correspond to the gears dimensions. So long as all of the dimensions of the housing correspond to these variables and aren’t referenced to the gear objects themselves it is fairly easy to swap the gears out with others.

This iteration of the design provides another approximately 2:1 reduction, which means that we should be able to shrink the transmission that was designed in the last post.

Rapid Prototyping – Use It!

This is more of a personal lesson, but perhaps it is worth reminding. If you are like me then you design something to 85% and then realize that you could have designed it better, then you repeat the process, without ever printing anything. With something that takes 100’s of hours to print that may make sense, but for tiny parts like this it is just foolishness. There is a lot to be learned by just printing the item, and trying it out as is.

These are pictures of the first functional assemblies, hastily printed in ABS (not printed on a Robox, I look forward to seeing how well it handles the small pieces though!).

Video: Assembly and Test

Some things are best expressed in video, and assembly is one of those things, so here we go!

 

Low-Volume Production of Formula 1 Parts with Robox

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For a great deal of parts such as the steering wheel plate and the brake pot hanger, the only alternative to Robox would have been folded aluminium. Not only does this increase the chance of the parts being incorrect, but it would have cost around £150-£175 for the steering wheel plate, and £75-£100 for the brake pot hanger, both with a 2-week minimum lead time.

Contrasting with Robox, the steering wheel plate cost £2.66 and was ready to fit in just over 3 hours. The brake pot hanger cost £14 and took 10 hours to print, which again is much cheaper and faster than any alternative.

Additionally, we find that in many cases, 3D printed ABS parts are also more aesthetically pleasing than folded aluminium, and seem to suit the nature of our cars. For example, the switch box design would not have been possible in aluminium; it would have simply been a folded sheet with wires protruding out the back. Not only is there a safety aspect involved, but the ability to create a sealed box with all wires and connections hidden looks much better than a folded metal sheet. Again, this is achieved with costs being reduced from around £60 to £5.37.

For parts such as the rain light cover, the only alternative to Robox would be injection moulded plastic, or carbon fibre. Again, these options are unfeasible, as both would cost hundreds of pounds. With Robox, the component cost £2.95, and was complete in under 3 hours.

Most of the tooling we manufacture is used to remove wheel bearings, etc. These tools are usually fairly intricate and cost in the region of £300-£400. With a trial piece printed to test fits, usually for under £0.50, we can be sure that these tools will be correct.

Overall, in the past year I would make a conservative estimate that by using Robox, we have saved at least £3,000 and reclaimed around 2 months of lost build time in comparison to alternative methods.

Tour De ForceMatt Scott, Design Engineer

Prototyping F1 Brake Bells

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Before Robox, we had no ability to prototype brake bells. The only option for us was to send them for manufacture, assuming our measurements were correct.

As you can imagine, a few parts came back and didn't fit, costing us hundreds of pounds, and weeks in lost build time.

The other alternative for components like this would be to send one for manufacture, receive it to check the fit, then go ahead with the remaining parts. However, this again is fairly unfeasible due to time constraints, and would still have cost hundreds for the single brake bell to be potentially wrong.

Ultimately, if the whole set of bells were incorrect, it would have cost us something in the region of £2,000. Robox, in comparison, used around £2 of plastic, and reduced prototype time to a single day.

We can realistically say that our Robox printer paid for itself with this one job!

Tour De ForceMatt Scott, Design Engineer

Ossum Racer, Part 2: Motor and Gearbox

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One day we will be able to 3D print functioning combustion engines in 1:10 scale, but for now the car will have to be driven by regular old electric motor, it’s sad but true, I know!

Why Reduction Is Needed

Small electric motors spin incredibly fast, but don’t generate much torque. In order to make them useful we need to gear them down appropriately.

Most RC cars get the majority of the reduction done in the first step, using a very small pinion on the motor, and a very large spur gear, but this is not really suitable for a realistically shaped gearbox, so I will use multiple stages of gears to achieve the desired reduction.

Design Goals

I have the following design goals for this reduction box.

  1. Motor must be low (for centre of gravity)
  2. Fully printable (without support wherever possible)
  3. Strong gears, big teeth, easy to print
  4. All gears to be hidden in a (semi) realistic enclosure
  5. Minimize unique parts

Selecting a Ratio

Although you can get a lot of power out of the “540” sized motors commonly used in RC cars, they still need a lot of gearing down, so it’s time to design a reduction gearbox.

I have done some rough “back of the napkin” calculations which show that a final drive ratio of about 8.5 will be decent starting point. The glory of printing is that we can experiment and revise once the car is working

Theoretical Max Speed Calculation
Example 1 Example 2 Example 3
Motor RPM 17000.00 22000.00 22000.00
Brushless Motor kV equivalent (2S) 2297 2973 2973
Brushless Motor kV equivalent (3S) 1532 1982 1982
Final Drive Ratio 8.50 11.00 8.50
Rear Wheel Diameter (mm) 95.00 95.00 105.00
Distance in One Wheel Revolution (mm) 298.45 298.45 329.87
Distance in One Motor Revolution (mm) 35.11 27.13 38.81
Speed (km/hr) 35.81 35.81 51.23

Gear Design

Although I did not use this tool to generate the gear profiles, I find it very useful for visualising a complete setup, you can follow this link to mess around with it yourself (link).

Gear Generator Screenshot

I decided on a stackable gearbox design, which consists of repeats of the same section, each one accounting for a 11/17 reduction in final drive ratio, resulting in a 5.7:1 ratio at the output.

This leaves room for a further reduction at rear axle (13/21, for example, would result in a final drive of 9.2:1)

Engine Model

Just because we are forced to use an electric motor doesn’t mean we have to look at one, so I began the design of a Merlin V12, scaled to 1:10. This engine will go over the electric motor, and given it’s size, probably also hide some electronics or the steering servo.

There are of course many details to go, but having the rough shape helps me work out the car’s final dimensions.

Gearbox Location

The gearbox can be orientated horizontally or vertically, which I am not yet decided on. I prefer the vertical orientation for aesthetic reasons, but horizontal may be more practical.

Either way, the motor stays at the lowest point, and the output is roughly in line with the rear axle input shaft.

 

Up Next

The next most pressing issue is probably to design the rear axle, and the telescoping driveshaft that will connect it to the gearbox, so stay tuned. In the meantime, I am curious to hear your thoughts!