Monthly Archives

May 2018

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.

AutoMaker Software update 3.01.00

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Robox AutoMaker software update is now live. Start your AutoMaker installation to find the update automatically or download it from here www.cel-robox.com/downloads/.

Your firmware will need to be updated as requested by the software, please note that the Robox will restart when the firmware update completes so be sure it has finished printing before allowing the update.

When you connect a Root or Mote device it will require an update to be able to communicate with AutoMaker, this will be shown as a button in the Network menu in AutoMaker preferences page.

Major changes:

  • Support for RoboxPRO
  • Support for SingleX head
  • Macro improvements across pre and post print along with maintenance functions
  • Major overhaul Root UI and backend to improve connectivity and transfer
  • Lots of functions added to Root
  • New SmartReel profiles and fixes surrounding programming locally and via Root
  • Linux settings page fixed (was blank)
  • Translation UI issue fixed
  • Reprint functions improved
  • Hardware warnings for abrasive materials dependent on head fitted
  • Lots of small changes to improve UX

A big welcome to our new software developers Tony and George, this is the first AutoMaker update they have worked and is just a small step on the path toward a lot of new content.

If you have problems a clean install might help.
https://robox.freshdesk.com/support/solutions/articles/1000155625-clean-install

Please create new posts for any problems you have.

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!

 

“Superb” 3D printing with Robox at King Edward VI Community College

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King Edward VI Community College

Our Robox 3D printers and the CEL UK-based support team have been superb. Students of all ages, from our primary school partners to Post-16 students, have all been able to access and use the Robox software and hardware systems effectively. They have inspired students and led to numerous STEM Big Bang competition wins. Further to this, our work as a community Fab Lab has allowed organisations and individuals to develop ideas on a personal level or commercially.

The Robox technical support team are second to none and offer excellent training materials to ensure systems are kept up and running. CEL are always keen to support users with emerging applications of their machines and illustrate their forward and positive principles.

I would recommend Robox to any educational establishment looking at purchasing 3D printing systems.

David IrishHead of Design & Technology