Event Horizon Beetle Weight Combat Robot Part 1: Design

Some Background:

My interest in combat robotics goes back many years. When I was in middle school, my father brought home a few books on the subject and I was enthralled. I thought up a few ideas, and had some vague plans to some day build a robot. And then I joined FRC 3467 and my combat robotics ambitions were superseded by FRC. A little over a year ago, after becoming frustrated with the state of the FRC team, I began looking for alternative robotics competitions. At some point, I started designing combat robots again (probably had something to do with the renew of Battlebots). Originally, my robot was supposed to be a 30 pounder, but as I started filling out those designs, I realized that it would be too expensive for my limited budget. Eventually I settled on a UHMW unibody 3 lb. drum spinner and created the first iterations of Event Horizon (EH). Since then, EH has gone through numerous revisions and two of those revisions have reached the point of being made.

CAD of the entire EH line may be found in this GrabCad folder: https://workbench.grabcad.com/workbench/projects/gcvuOsckFDIWLJdoowpnEofy4OMchZ2VH8DeKmusFdmL7P#/space/gcvl1rrfAIgrpm1Xv3alz6UXAZ9_w34lScfgpi5XAR6gS5
(Note: I re-arranged my GrabCAD projects and this link is broken now. I'll update it when it's fixed)

Event Horizon V1:

I quickly abandoned the unibody aspect of EH after concluding that my manual milling skills were not sufficient to actually make the frame. The design progressed to finger-jointed UHMW plates. After a fairly lengthy design process, I finally bought parts and machined EH 1 over winter break last year.

The frame of EH 1

Here is the completed frame of EH 1. The large chunk missing from the front of the right side plate was a milling mistake on my part. I can only imagine how horrible the results would have been had I tried the unibody.

Here is EH 1 fully wired and functional. I added wheel guards on at some point after these pictures were taken.

This is about as far as the EH 1 design got. I intended to compete with it at Motorama 2016 but Motorama 2016 fell on the last weekend of the 2016 FRC build season and as the design lead, I could not justify being gone at such a critical point in the season. EH 1 floated around my room waiting for me to find it a competition. But that didn't happen before I decided to re-design it.

Event Horizon V2/2.1:

Once the FRC season ended, several things had changed: 1) My father bought a CNC router, 2) I had spent a lot more time using the Bridgeport, 3) I had an internship at Foxx Life Sciences. These factors meant that I now had vastly expanded machining resources and money to throw at expensive robotics projects, which obviously meant that I was going to take on another robotics project.

After completing and testing EH 1, I was immediately somewhat dissatisfied with it. The weapon did not store enough energy. It was light, small diameter, and low speed. And so, a new robotics adventure began: make a robot with a really big weapon.

EH 2 began as a completely separate design from EH 1 and heavily utilized the CNC router. It used a strange drive train setup involving offset wheels for the ability to drive upside-down. It also used inverted motors, which I eventually deemed too space inefficient and changed. The front was a wedge, which was primarily designed for fighting wedge bots. (This is the Event Horizon v2 and Event Horizon v2.1 folders in GrabCad) I was about to order parts for EH 2.1 when I started having second thoughts. The odd wheel configuration was a liability as a spinner could easily take off the belts, the wedge probably did not have sufficient down force because of the wheel position, and the weapon motor was exposed and asking to be forcibly removed. Instead of buying parts for EH 2.1, I briefly tried to remedy the issues in EH v2.2, then scrapped the design and started over.

Event Horizon V2.3:

Frame:

For the next version of the Event Horizon design, I started with a more conventional wheel setup, using four 1 5/8" Bane Bots wheels, two on each side of the bot. The back set is direct driven off of two KitBots 1000 rpm gear motors (leftover from EH 1). The front set is driven via pulleys off of the back set. The smaller wheels and four wheel setup should make EH 2.3 slightly slower and easier to control than EH 1. Unlike EH 2.1, 2.3 has angled 7075 aluminum side armor, which is supported by UHMW blocks, and a UHMW plate in the front section to absorb spinner hits. The frame also has two ears at the top to prevent the drum from touching the ground should the bot be flipped over. Rather than the offset wheel arrangement of EH 2.1, 2.3 has an angled section on its top plate that exposes the wheels when the robot is flipped over. The front of the EH 2.3 frame is flat, which is not good for wedges. If I have weight left over after everything is assembled, I will add removable wedgelets of some sort to the front and may also make a set of removable ablative armor blocks for spinners.

Weapon:

For this version, I finally put the weapon motor inside of the drum (a result of getting the Hendey Lathe). Originally, I was going to disassemble the motor and machine a new housing for it to interface with the drum, but after receiving the motor, I realized that it would be easier to simply mount the entire motor  inside of the drum without modification. This has the additional benefit that it will make the motor much easier to replace if I manage to break it. The motor has a free speed of around 15,000 rpm at 11.1 V, which is fast enough that I don't yet feel the need to re-wind it (a boost converter may happen at some point, though). Initially, the drum had a titanium shaft running through it. This change in motor setup makes a through-shaft impossible and forced me to use separate hubs on each side of the drum. Hopefully this will not cause the frame to bend in after repeated hits. If it does, I will have to switch back to the original design.

When I first designed EH 2.3, it used a steel drum with steel bars welded on as teeth. I actually ordered the stock for this design, but since I don't know how to weld, I switched to an aluminum drum with flat head screws as teeth. I may go back to the welded steel drum at some point in the future, but for now, I want to get the bot up and running. You can see the various drum and motor designs in the EH 2.3 GrabCad folder. Common to all of the drum designs is an inset hub on each side of the frame. This is because the frame is made from UHMW, which is very soft. Repeated impacts on a small shaft would likely dent in the UHMW and cause issues over time. 

To protect the drive base, the frame pieces have some nubs on the bottom, which should bottom out as the wheels compress during a hard hit.

That's it for my summary of the Event Horizon design process. EH 2.3 is now in its final stages of machining. I will post a writeup of that when it is completed.