Redesign of Weapon Motor Mount

Due to poor design on my part, I've had to do a redesign of the weapon motor mount. I didn't have proper clearance around the weapon motor shaft and it was unable to spin up. I have since ordered some Aluminum Motor Mounts and plan on mounting them inside the chassis with this new piece that I designed.

Overall, I think this new piece should solve the issues. Potential issues with this part is it failing due to the force the motor exerts on it, however It has been designed to withstand a lot of force from the top plane inwards towards the center without having to rely too heavily on the screws that attach it to the chassis.

Parts Have Finished Being Fabricated

Pictured is a few of the pieces I had fabricated, everything else that was fabricated are just duplicates of the pieces already pictured. Top left is the drum pieces, top right are the side plates that mount the majority of the electronics, bottom left is the top plate, bottom right is the bottom plate.

I received the pieces back from TruFab on Tuesday. The parts came out beautifully all within the necessary tolerances for the other parts to press fit together with only some minor grinding. Currently doing a rough fitting of all the pieces and plan on rewiring once I see how much space I have to work with inside the bot.

When testing the weapon motor mount inside the bot, the component suffered failure in one of the mounting sockets, currently working on a redesign of the weapon motor mount and considering switching to this pre-made mount from Hobby King. However, this would require a redesign of some of the internal structures.

Final Fabrication Update

Side plates (left), drum pieces (top right), and the remains of the 4140 steel plate that the drum pieces were cut from (right)

I received an update email from TruFab this morning and attached was the image shown above. The side plates and drum pieces have been cut out.

It appears that what they have left is the side armor and top and bottom plates which will all be water-jet cut out of the 1/16" poly-carbonate, and the counter sinks in the side plates. Their machinist is out for the holiday so the counter sink work won't happen till either Friday or next week and the entire job is expected to be finished by mid next week. Super excited to get the parts and start the final build. There are some small adjustments that I will have to make in concerns to weight as the weight changed slightly due to the material change for the drum pieces. Possibly might have to go to 4 drum pieces instead of 5, additionally I want to design a front wedge/scoop using the Lexan to attach where the side armor will be attaching on the side plates to allow the bot to win battle for the low ground.

Final Fabrication

After doing some asking around, I ended up finding a local sponsor. Big thanks to TruFab Stainless here in Bloomington, Indiana. They have generously offered to donate their time to fabricate all parts that are needed for the robot.

I made my way up to Indianapolis the morning of 6/26/2019 to visit a couple stock metal and plastic businesses that I have been talking to. Ended up getting my 6061 Aluminum and 4140 Steel from Metal Supermarkets Indianapolis, and my 1/16" poly-carbonate sheet from Auburn Plastics & Rubber. Both of the supplier businesses had fantastic customer service and were very nice, would highly recommend either one for low volume orders of stock supplies.

After I finished picking up all of the stock I made my way back down to TruFab back in Bloomington. I got a chance to meet the staff and everyone was super friendly and taking in interest in the team, as promised I will make my way back over once I have the bot all finished to show them what's been going on. Once again, many thanks TruFab for their donation to the team.

Final Weight Estimation

With the CAD model completely finished, we were able to do a final estimated weigh in. All of the electronics have been wired and soldered, and could do with significant wire length shortening to cut even further weight. All weight is accounted for except for the spacers that will be used between each weapon tooth. Additionally, we counted out all of the hardware that will be needed to assemble the chassis and also added that to the weight. Currently, based on the current estimate the bot is 1.3 grams over weight, but we believe we can more than cut that with the re-wiring that will take place after fabrication. If absolutely needed we can go down to 4 weapon teeth instead of 5 which would cut 30 grams. Currently the weapon assembly makes up 20% of the weight, and will be able to spin up to ~8-10k rpm. We plan on probably not running weapon at full speed just because it's usually more effective to have a bigger bite.

This is the final bill of parts and their expected weights. Parts that do not have a volume and only a weight we weighed on a gram scale to get an accurate weight of the part with all of the wiring that is currently attached to them. We think we can significantly cut weight though as currently there is an excess of wires inside of the chassis.

Honeycomb 3.0

Rough Fitting, Weigh In, and Improvements to Make On Honeycomb 2.0

Rough Fitting

All of the main structural components finished printing on Thursday evening and were available for pickup on Friday morning. In the final design we plan on switching out the bottom, top, and side plates for 6061 aluminium and increasing the infill for the mid and back plate to 100%.

We did a rough fitting, not screwing in all screws, but just checking to see if parts and electronics are lining up the way that they should be and to check the clearance's of the holes.

The electronics look messy, but we plan on cutting down and re-soldering all the wires to appropriate lengths to cut weight and free up some of the clustered space in the internals.

Below is a list of components used in the build

Component	Name
Drive Motors	720 RPM Planetary Gear Motors
Weapon Motor	Turnigy 2836 Brushless 450-Size Heli Motor 3700kv
Drive ESC	Scorpion Mini ESC
Weapon ESC	Hobbywing X-Rotor ESC - 40amp
Battery	Turnigy Graphene 1000mAh 3S 75C Battery Pack

Weigh In

For the weigh in we went into Autodesk inventor and found the volume of all the custom parts (excluding the drum and side armor), then calculated the mass of the parts based on material density and the volume. We also had a scale to weight out all of the components IRL to account for their weight plus the weight of wires and connectors. In total the weight came out 1170 grams, which leaves about 200 grams for drum and side armor which isn't enough. This weight account for the bearings, shaft, gears, and shaft collars that will be used on the weapon assembly leaving the weight for only the drum.

Places to cut weight from:

1. Midplate, instead of a 8 way cross hatch, cut it down to 6 way (diagonals and vertical only). Cut down the material between the holes to mount the top and bottom plate.
2. Sideplate, instead of a 6 way cross hatch, cut it down to 4 way (diagonals only). Maybe, add some holes behind the bearing mount to cut more weight.
3. Backplate, instead of a 8 way cross hatch, cut it down to 6 ways (diagonals and vertical only). Cut down the material between the holes to mount the top and bottom plate.
4. Bottomplate, maybe double the honeycomb design to the bottom plate may present structural issues for mounting ESCs, battery, and radio receiver.
5. Electronics, clean up wire lengths to whats needed. Currently a lot of extra wires present in the build can probably cut 30+ grams.

Out of all the places to consider cutting weight my most hesitant place to cut weight from is the bottomplate and sideplate behind the bearing mounts as this might negatively effect structural integrity. We think the most drastic weight cut will be from the plating since those will be the largest amount of material removal.

We will also weight out all of the potential hardware that will be needed to hold the bot together (screws, nuts, washers, etc.) This weight will probably be even with any weight we cut with electronic's clean up

Improvements/Changes

1. Increase hole size for all 6-32 screws to a .144" clearance holes.
2. Move the centers for the top and bottom plate holes and mounts on the plate to be 5/32" instead of 1/8", idk why I didn't do this to start since a 6-32 nylock nut is 5/16" not 1/8" wide
3. Increase hole size for weapon motor mount to m3 clearance holes
4. Increase hole size for weapon motor shaft to clearance hole for a 3.17mm shaft
5. Increase hole size for drive motor shaft to clearance hole for a 4mm shaft
6. Taper the connection between the plates by 1-2 degrees to allow for easier slotting.
7. Change the tolerance on the shaft connection for the drum so that it is a close slide fit, not a interference fit.
8. Change the tolerance on the bearing mount to be a soft interference fit.
9. Add slot for weapon motor wires to clear to allow flush fit.

Fabrication of Honeycomb 2.0 Prototype

Once again to fabricate we used the IU 3D Print Lab. Currently we have the top, bottom, and side plates printed. The rest of the bot is currenlty on the printer and is set to finish up this Thursday around 8PM if I did my estimate correctly. This time we used the Ultimaker 3s instead of the makerbots, this allowed us to use dual extrusion to print some of the more intricate parts on the build.

This time true to form the top plate is now indeed Honeycomb.

The bottom plate finished up cleanly.

Don't know if you can see it here, but we had some issues with warping on the edges of the side plates. For prototyping this shouldn't really matter, but we wish it looked better :(