Prototyping and Build
Shooter Production Prototype
By Aliza G and Lariza S:
After finally finishing doing the last few tests with our last shooter prototype, myself and a few others have just gotten started on constructing the production shooter prototype.I’m really hoping that the third time will be the charm! In the last few meetings, I got the chance to work with the laser cutter. I learned a lot and had a bit of fun with it, and along with that I feel a lot more comfortable using it, even though my hands ended up covered in soot from the MDF we were using. Near the end of that same meeting we started assembly and I can’t wait to see how well this new iteration will do!
We have assembled the majority of the components. That includes the base itself, wheels, rollers, and most motors. For the following week we aim to adjust and tweak minor issues, finish adding the rest of the motors, wire it up, and most importantly: test it! We hope to learn how the shooter will do, how effective it would be, and - most of all - find ways to improve it.
[Brendan: This MDF version of the shooter is intended to verify that we have all the geometry correct before we cut the real thing out of Delrin (or possibly aluminum in a later revision). It’s already shown us a few places where the design needs to be tweaked a bit to eliminate interferences with standoffs and fasteners. MDF is not very strong, so we will limit the number of shots we make before we upgrade materials and take extra precautions so that no one gets hurt when it inevitably breaks.]
Intake Revisions
By Owen D and Grace E:
Over the past week we’ve been assembling [and then disassembling (and then assembling again)] alphabots intake.
Our first iteration included two ~90 degree turns before being fed to the shooter. This mechanism extended 5 inches past the wheels, but we found that the notes would stall unless more force was applied and had much trouble centering.
We made a couple quick “tweaks” to this prototype:
- We floated rubber on to the second set of rollers to give them more grip.
- We added some lubricant (WD-40) to the plates (as a stand in for slippery plastic)which proved to work close to the same.
- We then added a new motor as the original wasn’t in great condition.
This fixed many of the torque problems (starting and stopping when the note is ½ way in).
Another idea we had was that the front roller was doing more harm than good by pinching the note on the ground before it intook. To combat this we added a ⅛ sheet of lexan under the wheels to raise the intake (and the top roller) so that the front roller barely made any contact with the note until it hits the back roller. This proved to work well as the notes became more “touch it own it”.
Centering the note has also been a problem we are trying to solve. The original design with 3D printed wedges at ~45 degrees didn’t work very well for very off-centre Notes. The note either slipped on the rollers, or squeezed out of the chute rather than go around the wedge. This is similar behaviour to what other OA teams like 4561, and 6838 have experienced:
Our first idea was to add 4” wheels on bearings to let the note slide itself into the centre, but this did not work much better than the wedges for very off-centre Notes. Our second idea was to shorten the length of rubber on the very top roller to ~7”, this would allow the note to only move on the grippy part and self centre. but this also did not work, as it was too short and the Note would end up straddling the rubber. When we lengthened the grippy section back to 14”, the same problem as before kept occurring.
While we tested all these solutions, our cad team designed new side plates for the intake. We increased the width of the intake from 5” to 6” in front of the Chassis, which allowed us soften the bends to about ~60 and ~45 degrees instead of two 90 degree turns.
Rev 2 CAD:
Rev 3 CAD:
Once we had those laser cut, we assembled the intake once again and the different was immediately clear, as the notes now go a few feet further from where they went before.
By Brendan:
So we’ve made progress, but we have more design and testing to do before the intake is complete. Some ideas we’ll be trying this week include:
- Using omni or mecanum wheels rather than rubber tubes for the second rollers, before the wedges, such as demonstrated by Joe Johnson.
- Putting the 4” vertical-axis wheels after the second rollers but actively motorizing them like 3467 has shown to work. This will probably work as a last resort, but it’s another powered mechanism which would reduce overall system reliability.
Hopefully we find a solution quickly, as the intake is behind schedule. But it’s great that we’re learning these lessons now, rather than closer to competition!
Climber / Elevator:
By Me:
We have only just started moving the climber from design to production. We found barely enough room for the motors and gearboxes that will be required by forcing the Shooter design team to redesign their motor layout:
On Saturday we laser cut some climber parts from MDF. This week we’ll assemble a climber mockup with some scrap aluminum tube and on old chassis, and test it to verify that our geometry gives us the 18” of lift required for our Trap scoring plan to work, similar to what 3847 has done weeks ago.
