Team Eventorizon: Build Diary

[Ellis]

Surely ti is no harder than a high tensile bolt?

Some support for the turned bits (radius above and below) wouldn't be a bad thing. All of the forces go through those shafts. Also I'd be inclined to make the difference between the offset teeth smaller so you can have more thickness in the main body of the thing. At the moment the hitting edges of the beater are relatively weak: you have reduced width, no radii on the insert cutouts and holes through the lot.

[Eventorizon]

I seem to be second guessing myself today. I take things out thinking that people will say don't bother then I get advised to put them back again :-P

Putting the Radii back on the inside is no issue but adding them to the shafts is a pain not only to machine but it means that I have to make matching spacers to go on either end. Its not that much effort compared to making the weapon but given the shafts on the original didn't bend and D2 is even less likely to bend I don't think its necessary.

[Niels - Team K.a.L.M.]

In the end it's still your machine. Do what you want and take advise where it is needed.

[overkill]

The radius doesn't have to be large; my eggbeaters have about a 1.5mm radius around the shafts and have been fine so far. I also have spacers on the shafts and I just added a simple chamfer inside the spacer to clear the shaft radius - it only added a few minutes to make each spacer.

Cutting the radii around the teeth can be partly done in the waterjetting stage and the pockets for the inserts can be machined out with a rounded edge end mill. I have used a 1/2" diameter cobalt steel cutter with a 0.06" edge radius to pocket S7 steel and the parts have not stress cracked in 6 years. Rounded edge end mills are very durable and outlast regular end mills by many times. My 1/2" end mills cost $34 and are probably the most used cutters I have.

[Eventorizon]

You and all your handy hints Nick! You need to write a book

[overkill]

I would, except I have the attention span of a goldfish

[Eventorizon]

I decided to start on the electronics of my new spinner beetle. I knew everything needed to be tight and compact and given that I am running on 4S to get the most out of the weapon motor, this presented a few problems.

The first is that the 10A Botbitz don’t take more than 3S so that put them out for drive ESC’s. Second the battery was going to be quite a bit bigger than the 3S in Anvil and the other beetles which would make the chassis larger and thus heavier. Finally running full power on the weapon motor meant I needed to get the larger ESC, a 70A Red Brick, taking up more room and weight.

I was going to use the 12A-RC Sabertooth I had lying around from an old feather design but then I remembered… my Antweight. I had got a 5A-RC Sabertooth for an antweight that never made it beyond CAD.

Looking up the stats I was pleased to see that it took 4S and was far smaller than the 12A. 2 hours of staring at the parts later I ended up with this…

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After removing the Red heat shrink and the pressed Alu heat sink on the Sabertooth, I put some thermal compound on the 5A’s Fets and with a glue gun secured it to the top of the secondary heat sink on the Red Brick.

From that I ran wires from the Red Bricks power terminals up to the 5A to get power to it and simplify the wiring. After pre-attaching wires for the drive motors and grouping together the signal wires neatly I shrunk the two ESC's together into one compact unit.

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Sabertooths are known for not being too reliable in combat if they are not protected or reinforced. Here the heat shrink keeps the capacitor in place and I also added some extra glue to the base. All the internal wires are heat shrined together in pairs and clusters so any stress is spread across all the connection points and now rather than being over 35mm high the whole unit is now 27mm, just enough height left for some Velcro to go in the 30mm tall chassis.

There are some down sides to this design. Sharing heat sinks is one issue and possible overheating. Also if anything breaks it means the whole unit has to come apart which might take two long at an event. However this should be a good first version which I can improve on over time.

[harry hills]

Nice package (oo er) You might get some overheating issues with sharing a heatsink. That would be a worry for me.

I had more or less the same setup in eggbeater until the sabertooth died and I shoved the 10a botbitz back in, they were cooler than the sabertooth on 4s for me.

Looking forward to seeing some more beetle stuff

[maddox10]

After rereading.

Titanium bolts are comparable to 10.9 steel bolts. The weightdifference is only 3 grams on an M6x30 bolt.

Radii on machined pieces are a must. Even if previous experience gives the idea radii are overrated.

[Eventorizon]

The beetle arena build is drawing to a close so now I can actually start to think about other things, the first of which is our first non spinner robots.

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Going for small but strong. Dual GR01's driven by a Dual 25A Sabertooth, 6S 400mAh lipo as power and a 30V, 4500N, 100mm stroke actuator. I am torn at the moment between a 4 bar lifter and a crabber/crusher but that will mainly depend on what materials I can get my hands on. Unlike C3 and Binky this build will be more C1 and C2 style with HDPE and Polycarbonate making up most of the robot.

Will work on some CAD models but I think I will spend more time building prototypes in MDF this time as we now have an actual workshop space!