2363 tote stacker prototype

[ToddF]

FRC 2363 Triple Helix got our first tote stacker prototype working today. Now to start refining...



Video here.

[1629GaCo]

Great job guys, hopefully we will get to see it in action!!!

[wilsonmw04]

dude!!
Really, nice. I have a few thoughts.
1. Wicked use of a bike break.
2. really nice 2nd week prototype
3. Looks like alignment is going to be tricky for you to make this work well. What thoughts have you given to that?

[ToddF]

Originally Posted by wilsonmw04

dude!!
3. Looks like alignment is going to be tricky for you to make this work well. What thoughts have you given to that?

Lots of ideas floating around, both active and passive. Goal is to make it completely auto aligning

[Christopher149]

Where/how did you acquire the disc brake? Bought, donation?

[ToddF]

Originally Posted by Christopher149

Where/how did you acquire the disc brake? Bought, donation?

Bought at the local bike shop for prototyping. Much cheaper from Amazon.

[xXhunter47Xx]

Mechanical disc brakes are cheap to come by, you can find cheap Shimmy Shammy Shimano ones on Amazon. But I wouldn't be surprised if someone just ripped it off of an old MTB

[asid61]

Looks pretty good, however, I noticed that it tilts forward a little. might make it hard to stop when holding cans without toppling.

EDIT: how did you mount the bike brake? Can you get a closeup of it?

[ToddF]

Originally Posted by asid61

I noticed that it tilts forward a little. might make it hard to stop when holding cans without toppling.

Yep. Our prototypes are fast and dirty, with parts made with hand measurements and holes drilled by center punching then drilling by hand drill or drill press. We are just precise enough to prove a concept will work. Then we go back and refine and redesign. Final parts are made on the milling machine or other more precise methods. To take out the play in the elevator, we'll either make it more precisely, or redesign it so it can be adjusted level. (or both) If you take a look at our prototype videos from last year, and compare to the competition bot, you'll notice that weeks of refining may leave the final mechanisms quite different than initial prototypes.

[AdamHeard]

I like it.

[thatprogrammer]

What is the disk break doing in this mechanism? I understand it stops the load from falling due to gravity, but I'm slightly confused on how it's being used here. A picture from an angle showing how it works would help.

[ToddF]

Originally Posted by thatprogrammer

What is the disk break doing in this mechanism?

Brakes in a mechanism such as this are used to conserve energy and reduce the power consumption to the motor. If you use position feedback on the elevator, such as an encoder, you can use a PID control loop to hold position. Some of the approved motor controllers have microprocessors that can do the PID control right in the motor controller. Or, if you want, you can have the PID control loop happen onboard the robot RIO. Running the control loop on the motor controller offloads that computing power from the RIO.

The control loop applies current to the motor to drive the position of the elevator to the commanded position. If the elevator is very lightly loaded, it takes very little current to hold the elevator in position. The new interface tools to the robotRIO allow you to monitor the current the motor is drawing. As the load on the elevator increases, it takes more and more current to hold the elevator in position. With a full stack of totes, this could drain your battery more quickly, and can also cause your motor to heat up. If you have a mechanical brake on your system, you use the PID controller to quickly drive the elevator to the desired position. Then, you engage the brake and disable the PID loop. Now there is no current being sent to the motor. When you want to make a new move, you disengage the brake, make the move with the motor, and then re-engage the brake.

An alternative to using a brake is to choose a drivetrain which has lots of friction when backdriven. This could be a wormdrive gearbox, or just a very high reduction planetary gearbox/chain drive/belt drive combination. The high reduction maintains position even under high external loading. The tradeoff is that the higher the reduction, the slower the motion will be with a given motor. Also, the higher the reduction, the lower the mechanical efficiency of the system. In an industrial application, you might compare the energy lost by a less efficient drivetrain to the energy necessary to actuate the brake.

[thatprogrammer]

Originally Posted by ToddF

snip.

Thanks! My question was more " what is the brake gripping " though. Nice to hear the rational straight from the source though!

[notmattlythgoe]

Originally Posted by thatprogrammer

Thanks! My question was more " what is the brake gripping " though. Nice to hear the rational straight from the source though!

It is gripping a bike brake caliper.

[otherguy]

Originally Posted by notmattlythgoe

It is gripping a bike brake caliper.

...which is fixed to the hex shaft, which is coupled to the arms through chain.

Stopping the hex shaft from rotating prevents vertical motion of the arms.