Portable Apocalypse V2 – Motorama 2020 Upgrades

Since I have finally gotten registered for Motorama 2020, now is a good time to go over the intended upgrades to Portable Apocalypse. The overall design is remaining the same, but I am making significant changes to just about everything except the weapon disk setup.

Construction

The overall shape of the frame is remaining unchanged, but a lot of the little details are changing.

The top and bottom plates were previously made from 0.08″ grade 5 titanium, but now I am looking to change to 0.1″ 7075 aluminum, and increasing the width of the front weapon mount spars to account for the decrease in material strength. This should help free up some weight to be used in other areas of the bot, as well as decreasing the cost of the parts a bit.

New idea for a split top plate design for easier battery access

Going through a competition with the old frame showed me that having to completely remove the top plate to get the battery out for charging was more annoying than anticipated. Now the top plate design has been split into front and rear plates, with a dovetail design in an attempt to make the electronics compartment more accessible without compromising too much on the strength of the frame. Not needing to completely remove the lid also means that the weapon motor can now be mounted directly to the front top plate instead of needing standoffs/frame going all the way down to the bottom plate for a separate motor mounting plate.

The other problem with the electronics compartment of version 1 was that I apparently failed to leave enough room for all of the wires, leaving me to play a rousing game of spaghetti tetris every time I took the battery in and out. To alleviate this, the height of electronics compartment has been increased by 1/8″ and the length has been increased as well. Combined with some of the electronics choices this should give me plenty of room to fit everything and to hopefully add some padding.

New mounting scheme with square nuts press-fit into the 3D printed frame parts

Version 1 of the design used a combination of heat-set inserts, nutstrip, and actobotics parts attach the wheel guards and drive motors to the frame. After seeing the apparent success of the technique in the Vector kits, I have decided to change to using square nuts press-fit into the 3D printed parts to attach these parts instead. This should again help to make the bot easier to build and maintain without a major impact on durability.

Motors

The brushless drive motor setup that I used before was great for weight and power, but I could only use a fraction of the available speed/power without making it uncontrollable, having to keep the electronics away from the spinning rotor negated most of the space savings, and making the brushless-gearbox sets made spares both more expensive and more time consuming. As a result, now that the frame changes have freed up a little weight I have decided to go back to brushed drive, and I think that I have found some motors that would be good for beetleweight drive while still being cheaper than most of the typical options.

The 3530 motor that I was using for the weapon was working just fine, but the increased height of the frame makes it possible and perhaps desirable to make the jump up to a 3536 motor. Some estimation says that it could give me about 15% more torque than the old motor, so I’m hoping that will be enough to prevent the bot from doing “The Thing” if it gets propped up against a wall again.

Electronics

One of my losses at the Franklin Institure ’19 event was largely due to the failure of the weapon ESC. Rather than being related to the power used by the motor, it was more of an issue of my poor soldering skills causing a short with a bit of jostling. I have consequently sworn off bare-board ESCs for the moment, and I have found a new 50A ESC that comes with the power and signal wires pre-soldered so I can’t screw that bit up again. I’m also trying out soldering the 3.5mm female bullet connectors directly onto the solder tabs to save space on wiring.

The change from brushless back to brushed drive means different ESCs are needed there as well. I have some spare brushed ESCs floating around that can do the job, but I found a new cheap 2-channel brushed ESC that looks like it could do the job, so I plan on giving that a try before the competition to see if it could be a decent alternative. This ESC also has a built-in BEC, so it should eliminate two components and several wires from version 1 to help make the electronics compartment neater and less cramped.

Conclusion

I’ve got a lot of little under-the hood improvements in the works planned that should hopefully add up to a big upgrade and a more maintainable bot. I think that I have gotten the design of the bot to be very solid, now I just have to figure out how to improve the driver!

If the competition goes well and the design doesn’t show any serious flaws, I am seriously considering making this into a kit to sell online. Any interest?

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