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Theta actuation and pivot update

A project log for GimbalBot

Gimbaled thrusters, aerospace-grade adhesives, carbon-fiber-reinforced polymers, and inertial measurement units. This is a space project!

zakqwyzakqwy 06/17/2014 at 04:002 Comments

Quick update on v07. I modified the rotating thrust frame a bit so it's supported by a pair of rod ends; this is lighter, cheaper, and easier to align than the previous design that just showed a few holes through the CFRP square tube. I also started testing different servo mounting ideas; since I'm not as worried about servo weight or width (although both are important), I swapped out the slim servo from v06 for a standard 20x40 model. The unit I specified is insanely fast and powerful, and I included two in the model; again, I need to do some torque calculations to see if I can get away with a single unit (although they are only 60 grams).

Notably missing is the threaded rod that connects the two Heim joints. I've constrained them to stay aligned but haven't modeled up a longer rod yet. Also, I've added a split shaft collar on either side (visible between the stainless rod end and the flange mounted bearing here) to secure each shaft laterally. The split design should make this relatively easy to take apart.

On another note, Cubify has started to slow down. I'm using less than 25% of memory and CPU and my graphics card shouldn't be anywhere near maxed out, but I think the program isn't a fan of having so many individual parts and constraints in the assembly. I'm less worried about the slow speed than I am about the fact that it seems to have dropped a few assembly constraints; sometimes when I grab something that should rotate (such as the theta frame), it decides to drop an axle and move around a bit outside its intended range of motion. I might have just forgotten to constrain the model adequately; either way, I'm going to dig back in to doing nested subassemblies to reduce the complexity of the finished assembly. Anyone that's done this with Cubify Design--I'd love some advice. How do you structure your complex assembly trees?

ALSO, PARTS! Yup, more parts are on the way. Rod ends, split shaft collars, shafts, bushings (for the slip ring) and flange bearings should arrive later this week; I'm hoping the Rho brushless gimbal motor arrives around this time too (although it's got a much longer journey). I've also been bugging vendors about the GE power converter, so hopefully I can lock down a lead time for that unit soon. I'm anxious to finalize and construct the mechanical systems so I can move on to instrumentation and control algorithms!

Discussions

Peter McCloud wrote 06/19/2014 at 01:16 point
I have Cubify as well and I'm in the process of creating the assemblies and was curious as to how you had done it so I just download what you had and looked through it. Create job with the CAD! ( At work I create a lot of meshes from CAD files and most of them that I get really bad ) I have noticed it gets bogged down when you add lots of features and the constraints do sometimes act a little flaky. I think the nested sub assemblies will help you out. Great progress so far!

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zakqwy wrote 06/21/2014 at 02:32 point
Thanks for the kind words! I'm going to try subassemblies again for the next revision (or maybe for v07); I think the key is that Cubify assembly parts need to be updated correctly, so presumably the subassembly parts need to be updated correctly too. For instance, if you have a complex assembly and you change the length of a part, you have to make sure that you hit 'generate to last feature' on the part before saving it. Then you have to close and re-open the assembly. I noticed that when my assembly kept losing fillets; since they're usually at the bottom of a part's tree, they tend to get dropped.

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