I seem to recall a certain tiny vacuum robot winning a division last year with a bottom-mounted battery.
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And seeded to pick at every event
Mounting a battery on the bottom of a robot in a game with high spots on the field is not a good choice. The same can be said for bottom mounting the PDP and other critical robot components. Please review Sec. 9-7 and R8. While something may not be covered by a specific rule, doesnât mean it is a good design choice.
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If itâs a 6 sided box, how does it matter which side opens up so long as your ground clearance is still safe and the opening side is still secured well? What is the functional difference between what is being proposed here and a team who installs their battery in the bent sheet metal back part of the AM14U3?
Plus,
I can only offer advice based on a general description of the robot design. I have seen a lot of robots over the years, and only a handful that have used battery mounting under the robot effectively. We did it a long time ago and it didnât work that well.
95 has used bottom mounted batteries in at least two robots in recent years, and maybe a pre-season build. Aside from the minor annoyance of having to tip the robot over to effect battery changes, it wasnât a problem. We started last season with a battery mounted on the bottom, but ended up putting it on âtopâ so we could move it around to manipulate CG. You can see the original mounting position in this photo:
The battery slid into part of the frame and was secured to the wood deck with a big honking velcro strap or two. It held on fine repeatedly driving off the Hab2 platform.
Weâve also done a couple of upside-down PDPs. I recall being concerned that the breakers might fall out under vibration, but itâs never turned out to be a real problem. If anything, having most of the electronics upside down and under the robot kept game pieces and robots from whacking them, and swarf and debris to fall out.
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I have to remind everyone that there are a number of rules that specify visibility of components. In addition, if there is an issue with your robot on the field and the volunteers cannot easily determine the problem, you may be disabled and bypassed for that match.
Surely your main breaker is still âaboveâ, right?
Yes, as required by rule and practicality, the main breaker was easily accessible. The status lights on the robo-rio and radio were also visible.
Everything else went underneath.
In 2019, If you were a ramp bot IMHO as an inspector having most of your electronics on the underside of the frame pan with the breaker on the top would have improved accessibility, not made it worse. Also as one who has had to âreasonâ with teams about radio placement, PLEASE PLEASE PLEASE make sure your radio is placed high up and out of the way of electrical and metal frame interference!!! Oh and yes Iâve seen plenty of teams with inventive ways of securing the battery, though almost all of them were in the lower part of the frame because they wanted the added weight down low.
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For you (or other teams that put electronics on the bottom) - do you do anything special to try and prevent your electronics getting snagged by say the bars around the shield generator or by driving over any game pieces?
It is always safer to cover the electronics panel with a protective panel regardless of whether it is facing downwards or it is on top.
When I was the electrical mentor for Disco, their 2014 robot had most of the electronics on the bottom with a polycarb cover. We didnât have any problems though after a match, we panicked when we found some PWM cables wrapped around one of our axles. After some investigation, we concluded the cables had fallen off some other robot and we ran over them. If we didnât have the cover, those cables could have snagged some of our wiring.
We had a ramp bot team in 2018 whose ramps when folded were basically huge sheet metal wings on both sides of the robot that stretched the entire robot height and length. The radio was mounted right between the two sheets. From the FMS monitor you could see their signal strength fall and trip times rise whenever the robot was facing sideways relative to the FMS radio. When they turned back to face the FMS radio their signal strength went right back up and trip times went back down. Luckily it didnât end up being a problem for them, but itâs good motivation for thinking about your radio placement when designing the robot.
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@Andy_A, what is that zipper-looking stuff youâre using as cable runs in post 26?
Good point, there! If you plan to start with charged air tanks, either make the battery swap nearly instantaneous, or have a way to run the compressor in the queue with a âlooseâ battery while the new battery is already in place, so you can ⌠make the battery swap nearly instantaneous.
We (1923) put our battery in a location where it could only be installed from underneath. The picture below shows our solution. Essentially there is a box that holds the battery captive on all sides except the bottom, and then we utilize an aluminum plate with 4 1/4-20 bolts to secure the battery. The leads plug in on the topside. We always had a second battery (usually the one from the match prior) to top off the tanks in queue. This worked very well for us and I won a high-stakes bet with our Lead Mentor as we made it through the whole season through divisional elims without the battery ever falling out or otherwise failing.
We also used the same method this year along with mounting all of our electronics underneath the robot as well. Of course we mounted the bellypan to the top of the driverails and then added a lexan cover to ensure we kept our debris and guarded against impact.
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I would also emphasize that rules regarding visibility refer to very specific components, not universally, and that any team who is on the edge of these rules should be very familiar with them, since they are often misunderstood by both teams and inspectors.
For those who are not familiar with these rules (and their summaries from the inspection sheet) are (adding bold for emphasis, since some are in specific situations):
- R43 The single 120A main breaker must be readily accessible with labeling preferred
- R44 The single PDP and PDP breakers must be easily visible for inspection
- R64 A single OpenMesh OM5P-AN or OM5P-AC radio must be powered via a VRM +12 volt, 2 amp output. The VRM must connect to the dedicated +12 volt output on the PDP. Radio LEDs are easily visible
In addition, inspectors must be able to verify other relevant rules (around things like circuit breakers, wires, pneumatic tubing) were followed, and electrical systems should be designed to allow these things to be verified.
While it is true that making sure that other components are visible for field personnel is generally a good idea, outside of the rules, teams do not have an obligation to ensure this is the case and robots are not illegal when this is not the case (though hopefully this decision was made intentionally and the team is willing to accept the risks involved).
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The photo was of a previous years robot. This years robot used a more conventional belly pan with right side up electronics, so it wasnât an issue.
Some flavor of Wire duct. It comes in all sorts sizes and configurations, and does a good job of keeping wires restrained while being pretty easy to work with; just stuff the wire into it or pull it out. Itâs not the most space efficient or pretty system, but we enjoy not having to deal with 80 billion zipties in our wiring harness.
A closer view from this years robot during the build;
https://i.imgur.com/BKlbWDD.jpg
Wires can enter or exit anywhere along the duct.
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To expand:
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My favorite part of having upside down electronics was a near-perfect lack of swarf in all of the electronics components.
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The only reason we did âright side upâ electronics in 2020 was our planned use of powered ground effects (since ruled illegal). If/when we rebuild for 2021 weâll consider going to back to an upside down electronics layout.
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Weâve done this same thing. We first did it in 2014. This year we did the updside down board again. That, plus the âonboardâ nature of the falcon speed controllers really improved the space we had to work with. Weâll stick with it if we can.
