Drum
The drum is where most of the issues from the original design originated. Here are the changes made:
- Added pin between sleeve and motor mount piece: This should prevent these two pieces from rotating in unfortunate ways and shearing the wires.
- Added internal steel nut strip: If the teeth get ripped out, it won't trash the drum (as much). The nut strip also acts as a keyway for the piece attached to the output of the motor.
- Removed clamping piece for motor output and replaced with a plate bolted to the face of the motor: The primary motive for this was reducing weight, but it also leaves more space inside of the drum for other modifications.
- Moved idler bearing from drum to frame: Making those press fit pieces was a pain.
- Added retaining rings and washer to idler shaft: This constrains the bending of the frame by putting the drum in tension when the two main frame pieces are pushed apart. I believe this will help prevent Silent Spring-induced explosions.
- Switched to a shielded bearing for the motor side: The open bearing got filled with dirt and other crap, which made it very stiff. It is best to avoid having the bearing filled with dirt.
- Added a nub in the frame piece that matches the wire cutout in the motor mount sleeve: This constrains the rotation of the drum and prevents it from pulling its own wires out as in the Gemini match at FI.
- Switched to a continuous steel blade for a tooth: It is inset into the drum and should be much tougher. I may not bother with this if I don't have enough time to do the machining.
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| Washer added to the idler shaft |
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| Keyway nub to prevent rotation |
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| The internals of the drum |
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| Full render of everything |
Drive Base
Most of the changes to the drive base were aimed at weight reduction. Changes made:
- Switched to brushless motors: They are lighter and should be faster. I'm planning on using these: https://hobbyking.com/en_us/turnigy-park300-brushless-outrunner-1380kv.html
- Back wheel is no longer direct drive: This improves the space situation and some reduction is probably necessary for the new motors.
- Front and back wheels are now different sizes: Improves packaging.
- Aluminum hex hubs are switched for nylon: Weight savings.
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| New wheel configuration |
Frame/ Armor
I made a lot of changes to the frame aimed at improving strength.
- Re-worked front plate mounting: Should be less prone to screws ripping out, etc.
- Extended belly pan forward: This will brace the frame further toward the front, helping to prevent the main plates from buckling.
- Switched from finger joints to pins to locate center plate: Fewer giant cutouts = less bad things.
- Moved belly pan holes: I moved holes to places that do not have as many holes, rather than just ignoring their existence. This should reduce the likelihood of catastrophic failures of the frame members.
- Reduced angle of side armor: I did not find myself needing it at all at FI and the weight savings are probably worthwhile.
- Removed middle armor support: The fewer holes the better and, again, I didn't really need the side armor.
- Switched to aluminum top plate: It should be stronger (and look better) and I think I have the weight.
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| The new system for the front corners |
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| What the inside looks like now (I didn't bother modeling the motors) |
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| Extended belly pan and holes strategically placed to avoid other holes |
Other Thoughts:
Hopefully I will be able to manufacture this over winter break. While there are changes that I probably will not get around to, I suspect this version will be much more competitive than the last. Some experimental things, like the brushless motors may end up not working, in which case I will switch them out for more known quantities.
For anyone interested, here is a (rough) bill of materials: https://docs.google.com/spreadsheets/d/1VzffXAeI5nw5pdMJEc_gqofo4VOdaDqT6vaQEu75xT0/edit?usp=sharing
