Gear Reductions for a Robotic Arm Using Fusion360
Introduction: Gear Reductions for a Robotic Arm Using Fusion360
My name is <PERSON> and I'm currently in a senior Queens College located in NYC, many of my students have uploaded projects for the Fusion360 contest, so may the best man win (or qualify)
This is my Instructables for how I used Fuion360 to model and print two different types of gear reductions for a robotic arm I'm working on. this Instuctables focuses on two types of gear reductions, Planetary and Strain wave (otherwise known as harmonic drive)
Ill discuss why I chose the gear reductions I did, as well as the steps I took to make them using Fusion360.
This project was heavily inspired by a video by 3DPrintedLife, who at uploaded a video right at the time I started brainstorming for this project. his design was perfect, but not suited for the type of machine I wanted to build. So they look similar, but the design is completely designed by me in Fusion360.
This arm will run on an Arduino UNO using a CNC Shield. I currently use GRBL to control it for testing
Supplies
Supplies needed
1) Laptop
2) Fusion360
3) 3D Printer
4) LOTS and LOTS of time
5) some various bearings
6) various screws
7) MORE TIME
8) The ability to cope with a lot of failure
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Step 1: STEP 1: Why Use a Gear Reduction?
Gear reductions are necessary for almost all motion using a motor, almost every dc motor uses some type of gear reduction, most commonly a spur gear reduction. It causes the motor to spin slower, but exponentially increases the torque output. The larger the reduction, the slower the motor will spin, but the stronger the motor will be. Most of it comes down to the kinetic energy put into a system.
So why do I need a gear reduction? I planed on using the readily available (and cheap) NEMA 17 stepper motors for my arm. the issue with this is that the motors are super weak. they really don't have much of a holding torque. and in order for my arm to be able to hold anything, it needs some decent holding torque, specifically at its base joint.
So it was settled, I need some kind of gear reduction, the question was... Which one?
Step 2: STEP 2: Which Gears Are Best?
Now, I'm not going to get into an argument as to which gear reduction is best, obviously each scenario requires different mechanical systems. In my case I needed 3 specific characteristics. I needed it to be a REALLY good gear reduction. I was hoping for a 30-1 reduction, meaning that when the motor spins 30 times, the output will only spin once. 949
I also needed it to be in a small package (bye bye spur reduction). Since I wanted this to be a desktop robotic arm, everything had to be in a small package. The last characteristic is that it needs to be CHEAP. I cant spend hundreds of dollars on bearings and spacers and screws... you get the point. Most of the parts need to be 3d printable, and I wanted the cost to be below 30 dollars per gear reduction, of which, 2/3 of it will be going to bearings anyway.
Because of these "limitations" I only had 2 options, planetary, or strain wave. Unfortunately the cycloidal gear reduction would've been too expensive bearing wise so I had to forget about using those. the question now is... what are those gear reductions?
Step 3: STEP 3: Planetary Gears
Planetary gears look amazing. their gear reductions are fairly simplistic. you have an outer ring gear, an inner "sun" gear, and the smaller planet gears. there's a lot of math involved in designing these, so I just used a planetary gear calculator on google to determine the tooth count. these gear reductions are back-drivable, and stackable allowing you to get some insane gear reductions in decently small packages. for example, you everyday drill have a stacked planetary gearbox to gear the speed of the motor down and to give it enough torque.
This is the planetary gear simulator i used to determine the tooth count and overall reduction for my first attempts
http://www.thecatalystis.com/gears/
Step 4: STEP 4: Designing a Planetary Gearbox in Fusion360
Since i had no idea how to design anything gear related in fusion360 I took to YouTube to offer me some guidance. There's an amazing series on gears by Antalz, https://www.youtube.com/channel/UC9_6o_CDwuqoVZ5H0...
and I highly recommend you check his channel out.
To skip over the bring math bits, I first used the Fusion360 plug in for Spur Gears. 737