I may as well design the retaining ring for the planets. gear teeth are 3.14 mm apart): Retaining Ring Still using a first Diametral Pitch of 1.0 (i.e. I had a play and I came up with a five planet design (25/20/65 and 20/60). It is possible to add more planetary gears by changing the outer gear ratios. If the MDF version work out okay I may look at an acrylic version. I suspect there a different grades of acrylic and the stress fracturing is a feature of the cheaper grades. It not very stiff and it stress fractures over time.It is assumed the retainer axles are not concealed.Īt this point of time I don't really thick they are needed in this application.Īcrylic (perspex) is nice looking material but has some undesirable properties. It is possible to add a 6 mm thick planetary gear retainer in the upper layer or a 3 mm thick retainer in the hub layer. If I did not have to make allowance for the stepper motor mounting bolts, the drop down into the layer with the hub, reducing the elbow thickness by two layers.White, red and green are the inner gears.The blue outline is a Nema16/17 stepper motor and mounting hub.The "gaps" in the layers are provision for mounting bolts.The yellow layers are the left arm and the cyan the right arm.The lower layer is optional but is designed to increase the joint stiffness: LibreCAD's polyline offset does not work so I will have to make this adjustment in the gear code. Given the gear teeth are quite small, an allowance for this probably should be made. The cut quality varies, sometimes he cuts too slow, sometimes his machine is out of alignment. The laser cut diameter for the guy I use is about 0.1 mm. Other bearing types (teflon?) may be considered later. However a paper spacer most likely will be required to give some bearing clearance. Where disassembly is required M3 bolts will be used to hold the pieces together.īearing surfaces need to be lubricated with wax or silicon spray. The final design will have 1 mm alignment holes and glued in most cases. The thickness need to be at least doubled. A single layer was no really good enough for the SCARA Prototype. The design is built up in layers using 6mm thick MDF. To calculate the Diamteral Pitch ratio use (57-21)/(60-21). This reduces the size of the gear set to ~75 mm diameter. I also increased the Diametral Pitch to 1.0 and 0.928571429. I am now using 24/18/57 and 18/57 gear ratios. Rather than increase the overall gear set size, I have changed the gear ratios to make the Sun gear larger (and the Planetary gears smaller) without chaning the outer diameter. I want make the elbow as compact as practical but the current Sun gear is too small for the stepper motor hub. (Well I could use VM VirtualBox and Windows with DeltaCAD!) Can't expect everything for free!Īs I have to run DeltaCad under Wine, losing the macro language and the fact it does not support PolyLine (only lwPoyLine), I have to migrate. Other issues are that some of the commands are not functional are rather primitive, "Polyline Equidistant" is an example. If you use CAD all day you will appreciate keyboard short-cuts (avoiding menu mouse movements) and minimal steps. LibreCAD is slower to use as most things need more steps. I should point out that DeltaCAD is not an AutoCAD clone. The DeltraCAD user interface is much better than LibreCAD from the point of view of minimum mouse/hand movements and less steps to do things. I am migrating from DeltaCAD to LibreCAD.
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