We are running into an issue where the battery needs to be loaded from under the robot, as our other subsystems interfere with battery placement. We would like insight if possible from other teams who have previously done similar battery mounting. We’re worried about certain mounting techniques that could cause the battery to fall out during matches but also want to easily access the battery between matches.
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A battery mount that loads from underneath may or may not work, but it is going to make the inspectors very nervous. The potential for a battery falling out on the field is just too great, and don’t forget that this will get you immediately disabled (per rule G101) and may result in other penalties, especially if it happens more than once.
We had a similar problem with our Steamworks robot and the solution was to cut an access hole through the front frame rail (it was a Kit frame) that we slide the battery through and into a secure horizontal mount. It kept the battery low in the frame, probably in a space much like the one you’re trying to fit your battery into. Since it was still inside the frame, over the intact belly pan, and had bumpers completely covering it, it worked out fine. That was the season that we developed our own quick-removal bumper system too, for fairly obvious reasons. 
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We did this with our 2020/21 robot; the battery is flat under the ball hopper, and there’s an access panel beneath it. The intention was to change batteries from underneath, and we did so at one event (the one we made it to in 2020).
It was not pleasant.
Battery swaps involved multiple students carefully supporting the robot on its side while other students removed the access panel, wrestled the heavy battery out, reached in and disconnected it, connected the new one, and tried to slip it into place without damaging or pinching any wires/pneumatic lines or dropping the battery. As there were several controllers mounted to the hopper immediately above, this was not easy, and there were times we’d do a systems check and find we broke something, and have to do it all again (after fixing whatever we broke).
After that event we never did it again. We would dump air, cut a couple of zip ties, and unbolt the hopper so we could (much more easily and carefully) exchange the battery from the top - not fighting gravity was worth it.
Based on that experience, my advice is to try very hard not to do a from-beneath swap, and if you absolutely must, make sure the access is as easy as possible and there’s nothing immediately nearby prone to damage during a battery-swap. And yes, do make sure whatever you use to secure it is not going to come loose and drop your battery (we did not have that problem).
Our rookie-year (Steamworks) robot had a flat-on-the-bottom battery too, but we were able to provide access from one side so it could slide in and out, with a hard-mount for the SB50 so we could reach in and connect/disconnect it. Maybe something like that is an option for you. I see @Strategic just posted that they did something similar for that game too.
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Would your team design the various subsystems in a way that would interfere with the wheels on your chassis?
Since the battery is a crucial component of all robots and easy access for replacing it is a “must have” feature, the other subsystems should be designed around the battery and the battery access space. If accommodating the constraints imposed by the battery and the battery access space is too difficult, it may be that the designs for those subsystems are too ambitious for the designers working on them and the scope of work may have to be trimmed back.
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Though I agree this should be avoided if possible, one thought that we had last year to help with our belly pan accessibility could help make this much easier.
If you designed your cart such that the entire door was accessible and just swung down to replace, that could mediate the time issue and some inspection stress.
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Our 2019 robot was designed to have the battery loaded from underneath the robot as it made packaging a lot easier for us. We created a cutout in our belly pan that led to an inverted battery tray and a plate that supported the battery from underneath. This plate had 4 holes that would allow it to be bolted to the robot securing the battery via a custom threaded “nut bar” that essentially eliminated the need for nuts and a wrench. To reduce change over times we would simply tip the robot back and use a particular electric screwdriver that would deliver just enough torque to remove and recasted the bolts without causing damage or risk crossthreading. This worked seamlessly through all our events and practice sessions. I’ll have to see if I can dig up a picture of the assembly.
In summary it can be done, but it should be done in a well planned, well executed and well practiced manner.
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Nope, it won’t.
Only makes me nervous if the implementation is unsafe.
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Our 2021 robot had a bottom loaded battery. It slide onto a shelf and is held in by a velcro strap, no tools required. It worked great at all the offseasons this past fall. We wouldn’t hesitate to do it again if the robot packaging benefitted from it.
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Our robot last year also had a shelf. It wasn’t too bad. I think this configuration did take some additional space to let it slide at the angle from underneath but was just held by velcro and I think it would pass inspection.
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We did it in 2020 and 2021 with no issue. No complaint from inspectors or anything. Just prove that it wont jiggle out. Any hook and loop tape worth its salt is viable. I would suggest creating a sawhorse station that allows you to put your bot on it and have access to the bottom so you can easily switch batteries without having to tip your robot. We don’t favor doing a bottomside mount just do to some hassle, but its necessary, full steam ahead. Hope this helps!
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Sorry, the focus wasn’t the battery box since these are unrelated (funny enough, these are both our tribute robots).
The blue robot (2020/2021) has 2 standoffs (made from Thunderhex) to constrain it forward/backwards and two standoffs to constrain it from falling out of the robot (up is handled by the bellypan.) The standoff by the battery terminals is removed with two 1/4-20 thumbscrews and the battery is pivoted out. The battery box is lined with foam to prevent it from shifting.
The white robot (2019) is encapsulated by a plate with 4 screws in it; these were screwed into standoffs mounted on the top.
I don’t think we ever came across an inspection issue with either of these nor have we ever had a battery fall out of the robot.
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Assuming it well designed and tested, the biggest annoyance is that you have to flip you robot over to put it in. It falls in the category of “Would prefer not to do, but if ya gotta do it, ya gotta do it”
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Could you expand on how your Velcro strap was routed and mounted? We were imagining something along the lines of the sketch below if we go with an idea like yours. Battery Mount Concept - Google Drawings
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Could you expand on how your Velcro strap was routed and mounted? We were imagining something along the lines of the sketch linked here. Battery Mount Concept - Google Drawings
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It is more like this: Nugget Battery Concept - Google Drawings
Two slots, two velcros doubled up and pulled against each other.
You want to wrap around if you can rather than hammock the battery.
I forget maybe the lower velcro goes up underneath (likely) to get tightest wrap. And if you have hook or loop on bottom or back I’m not 100%, either works but loop is better where there is a chance of hitting carpet, etc.
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Thanks for the replies! This makes a lot of sense, and I think we’ll go with this.
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As an RI:
Bottom Loading - not a problem per se.
Without a lot more details on what this looks like, there’s no way to give a real answer. For example, a KoP horizontal battery mount that’s loaded from below is likely OK. A design where the chassis constrains the battery up, back, left, and right and a bolted-in angle bracket constrains down and forward is likely OK. However, any situation which requires a bottom mounted battery has, in the words of a now-retired co-worker, “a lot of ugly potential”; you’re going to draw extra scrutiny. [not that that’s a bad thing, just a thing]
Bottom line: be ready to convince your RI (and LRI) that you’re in compliance with R606. If you have serious doubts that you can do this, you should go and re-think your life battery mounting.
R606 *Secure the battery. The ROBOT battery must be secured such that it will not dislodge during vigorous ROBOT interaction including if the ROBOT is turned over or placed in any arbitrary orientation.
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I appreciate the heads up sir, we have worked out a pretty secure system now and are nearly certain that it will hold. Thanks for shoe in as well, with what to expect during inspection.
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Make sure the execution of your battery retention system is of good quality and test it rigorously to confirm it works under all conditions. A great idea can be let down by poor quality execution. That is probably why some people are advising against installing the battery from the bottom.
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