[BW] GR-01 Build Diary

[J.A.G]

Look ace
can`t Wight to see some vids

[harry hills]

You will need to drive all the wheels. Your drum supports look lacking in material. Beef them up if possible. Other than that I'm a fan.

[Giles]

Ok I will pursue that wacky invertible plan Expect more detailed cad models soon.
Today I was rather busy, so haven't done a great deal yet. I did manage to model and 3D print some motor mounts however. I printed them in two parts, as I'm not sure if the back support is really necessary.


I'm starting to look at timing belts/pulleys. Is there a specific brand/size/type that people tend to use on beetles? Or does anything go? Also I assume I'm going to want a belt that is able to slip a little for driving the weapon? Or should I just use a timing belt on that too? Whats a typical axle diameter for a beetle too? The wheels I've ordered fit onto a 4mm shaft.

Sorry for all the questions

[Ellis]

As long as the mount doesn't mind the forces (3DP reliability is tricky in robots bigger than really tiny classes) you should be able to just mount from the front.

For timing belts, I strongly recommend HTD-series tooth profile. These can be had in 3mm pitch (search HTD3) which is ideal for beetles. They're extremely tough belts, I use them in bigger classes (5mm pitch) with success.

Weapon belt slippage (seriously you must be doing good research) is important, yes. You can either run the same HTD profile belt onto a non toothed pulley, which given the right tension will spin up fine (the yank from the brushless tensions the belt such that it grips like fury, but can still slip in impacts), or you can use ~4mm round belts in round groove pulleys. Less tough but more compact.

Weapon shaft diameter, I'd go no smaller than 8mm (assuming steel). 10mm feels right. If it's a drum you may need to go with titanium to save weight. For drive stuff, 4-6mm is the right region.

Edit: actually 8mm, assuming the drum bearings are positioned close up to the bulkheads, would probably be fine.

[Giles]

All that sounds good to me. Thanks for the recommendations.

For the 3D printed parts, I'm printing them in fairly brittle PLA plastic right now, but once I have prototype working as intended, I'll reprint them all in carbon fibre, which will hopefully be nice and light and strong. I don't have any other tools for making parts like these really, so its either 3D print, buy parts or send CAD files off to be milled (never done that before, no idea on costs)

[Giles]

More cad doodling. A lot of stuff to figure out with the weapon and chassis still, but I'm starting to like this design. At the moment its using 10 toothed HTD3 pulleys, I've found these in 10mm belt thickness, wondering if 5mm can be obtained somewhere? I've used 5mm ones in the CAD drawing on the secondary wheel drives, but I'm not sure if they exist, couldn't find any myself.

[Ellis]

Looking really good. I use http://www.beltingonline.com/ for all things transmission, they have standard HTD widths but can also cut to any width you want.

[Giles]

Cheers Ellis!
More cad work. I'm about ready to ditch 123D Design and move everything into inventor. Getting frustrated with the limited amount of tools now (especially when wanting to make belts).

Heres a lil more rough design work. Moved the belts inside the frame for safer housing and more compact walls, moved the motors back to directly drive the rear wheels and thought a bit more about the drum mounting. Hopefully when I get everything into Inventor I'll be able to solve design issues faster.

[Mouldy]

like it!

[Max]

Design looks awesome!

If you are limited in terms of manufacturing capabilities you could easily get those side panels laser cut by a company like laser-master depending on material.