Build challenges, and some advice (maybe)

[CloakAndDagger]

So, as everybody knows, this years challenge was extremely tough on robots. As a result, many teams suffered breakages throughout the year.

Lucky for us, we didn't suffer many match-affecting failures that we could have prevented(usually faulty parts), and as such, I thought that it might not be a bad idea to share our experiences with other teams.

I'll kick the thread off with our main problem: we are a scaling bot, and our scaler worked excellently throughout the season. However, when we scaled, we weren't always above the low goal(the arm went up and pulled itself along, but the base was still touching the ground) so we used the motor driving the arm to rotate the rest of the robot up, so that we would score. However, this puts tremendous strain upon our hex-shaft axle, and it twists about 80° every 12 matches or so. It doesn't effect how we operate, but we would rather not replace a shaft every 12 matches. Any solutions?

For reference, we use a 300:1 rs550 as our motor and gearbox, and a 3/4" water-hardened steel hex-shaft

P.S. Should this be moved to technical discussion?

[Jonny_Jee]

To the first half, I have always tried to design each part in easily changeable modules. this served 2085 especially well in 2014 when parts broke frequently, but could be quickly and painlessly replaced.

Next, and this is a big one, make the robot as simple as possible. If you can implement a passive mechanism in an actives stead, you're removing complexity. In 2015, we got away with using single motor and no pneumatics to do all manipulating, faring well in competition.

And for the shaft, have you made the gap connecting gearbox to arm as minuscule as possible? or reinforcing the shaft with a broached steel sleeve?

[Knufire]

Based on this, it sounds like you are driving your arm rotation by powering a 3/4" hex shaft off the motor, and having the arm locked to the hex shaft with some sort of hub with the appropriately broached 3/4" hex hole.

For extremely high torque applications such as this, I would advise mounting the arm on a dead axle vs a live axle. A common way to power high torque arms is to directly bolt a 60T #35 chain sprocket to the arm structure, and have the arm supported by bushings or bearings on a rigid shaft attached to the robot frame.

[CloakAndDagger]

First, yes, we shortened the gap as much as possible, and we have a hex broached sleeve on it. We don't have room for a secondary axle.

I was actually posting that more as an example than anything else. We are pleased with our arm as it is, it is simple and we can swap the shaft in 20 minutes or so. However, I love the fact that people were able to offer great ideas so quickly.

What problems have other teams had?