Is this legal? Custom Battery Assembly

Had a student over the summer design a quick release battery system that has some 3D print parts that hold the connector in a specific orientation and mounts to the battery.

I’m sure others have thought about it but I have never seen a team try this so I’m guessing there is some rule that makes adding to the battery illegal. Scoured through the game manual and could only find:

R609 *Connect main power safely. The 1 ROBOT battery, a single pair of Anderson Power Products (or
APP) 2-pole SB type connectors, the 1 main 120-amp (120A) surface mount circuit breaker
(Cooper Bussman P/N CB185-120, CB185F-120, CB285-120 CB285F-120, CB285120F or Optifuse
P/N 153120, 253120), and the 1 power distribution device (CTR Electronics Power Distribution
Panel, PDP, P/N am-2856, 217-4244, 14-806880 or REV Robotics Power Distribution Hub, PDH,
P/N REV-11-1850) shall be connected with 6 AWG (7 SWG or 16 mm2) copper wire or larger, with
no additional devices or modifications (with the exception of monitoring circuitry permitted by
R625), as shown in Figure 9-10

Seems that this is referring to the electrical modification and not the mechanical. Not sure if this would fly in inspection.

We are still using the same wiring connections. Nothing changes electrically.

Thoughts from anyone?

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I think it is reasonably common to use the mounting holes in the APP connector to fasten (bolt) the “robot end” of the connector pair to the robot. To me this is an extension of that idea and as long as neither the connectors nor the battery are modified, I’m not aware of a rule that your design would violate. There are no unwritten rules. My personal opinion (worth exactly what you paid for it) is your design is legal (under the 2022 rules, and likely under the 2023 rules).

Well done to your student for an intriguing design.

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The tricky part is R103 (b):

ROBOT battery and its associated half of the Anderson cable quick connect/disconnect
pair (including no more than 12 in. (~30 cm) of cable per leg, the associated cable lugs,
connecting bolts, and insulation)

The weight of the battery side 3D printed assembly must be counted in the robot weight since it doesn’t fall into the cable part of the (b) exclusion, but it’s unclear how you would do that.

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I would agree on that. It could be interesting to ask Q&A if other battery-mounted hardware would be exempt as well, though.

I do have a few questions for the team.

  1. How does this attach to the battery? Anything involving drilling into the case is going to be Right Out, for obvious reasons, but I’m not seeing another way the battery would connect to the housing.
  2. Has this been tested against, er, strong loads? e.g., if someone accidentally picks the robot up by the battery handle, what breaks? Does the battery shake loose easily when hit? Can the battery release actually be released easily–or, could an opposing robot reach it?
  3. Speaking of the handle, is it strong enough to support the battery? (It looks like it could be. I’m a hair concerned about 3D-printed parts cutting loose there, though.)
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Obvious standard disclaimer that this is up to the LRI at your event (and may be worth a Q&A during the season once it opens).

That said (assuming no changes to the battery rules), if this was at an event where I was the LRI I would:

  1. For the weight rules Peter mentioned:

    • Have you bring an extra battery-side 3D printed assembly NOT attached to the battery and weigh it with the robot.

    • Do a quick visual inspection of your batteries just to check that all of the handle attachments look the same.

  2. For the no-battery modification rule, have you show me how the handle attaches to the battery just so I can know for sure that it doesn’t attach in a way that requires modification (ie, you didn’t have to drill through any of the battery plastic to attach bolts or anything, as that’s a no-no).

So this seems like it’s inspectable without too many issues at an event.

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I think this is really clever and I like it.

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I would definitely ask on the Q&A when it opens up.

In addition to what others have said, what about the vents on the top of the battery?
@Al_Skierkiewicz knows these batteries better, but there may be a concern about those vents being able to do their job once trapped under a handle like this.

I’m also curious how the handle will hold up. Batteries are pretty heavy, having something 3d printed like that may break during normal use, depending on materials, print quality, print orientation, etc. I’ve seen layers separate on prints with less force applied than the battery weight will. I’d recommend building a few and doing some failure testing on it (without involving a battery!). Build a jig that lets you apply a known amount of force on the handle, see how much it can take. Assuming the breaking point is significantly more than a battery, then cycle the test (at a force larger than a battery but less than breaking force)many times to simulate multiple pickups and placements.

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It seems to clamp into the “finger holes” on the sides of the battery top, iirc a few teams have designed handles that interface in this same area.

I’d also recommend a COTS handle here depending on how layer orientation works out, but even then.

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Not commenting on the legality, but I do see a major downside here from an electronic standpoint. The battery is very heavy so it carries a lot of inertia and will wiggle around when the robot takes impacts. Normally this isn’t so problematic as long as the battery is kept relatively contained because there is stress relief (i.e. the battery cable) between the battery itself and the Anderson connector. But now if the battery and Anderson are physically connected, the inertia of the battery could dislodge the connection, even momentarily, and cause the robot to reset. I’ve seen before where a team bolts the Anderson to the robot frame and a big enough hit causes it to come unplugged, even without having a whole battery attached to the other side. This is why I generally recommend having the Anderson connector free-floating and secured with a zip-tie before each match.

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Wouldn’t necessarily recommend, last time we did this we ended up with a broken lug inside the robot due to fatigue when the connector would get yanked in connect/disconnect cycles

Yes, 100%

I’ve seen some teams that mount an extra handle onto the battery plug to allow better grip when unplugging. I’m not sure how that has been ruled previously and this is obviously heavier but it should be ruled similarly if there’s no rules making the distinction.

If the handle breaks off, is it possible to get the battery back out?

What bend radius is required for the two battery cables connecting the battery to the SB50 mounted on it. Depending on the type of cable, the minimum (inside) bend radius is 2x to 12x the overall diameter of the cable.

How likely is it for the SB50 on the battery assembly to not align properly with the SB50 on the housing? Everything is “perfect” in CAD but the world is never perfect.

You may want to add a feature in the lower housing that will allow a cable tie to be used as a strain relief for the cables coming out of the SB50.

What is the dark grey part in the housing opposite the SB50 going to the breaker and PDP/PDH? Is it a latch of some sort?

image

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Yeah if the intention is that they have dial input I’d be curious if that’s allowed.

Looks like a latch to me. Couldn’t tell you what type from here, though.

Dual input from the battery, nope, you get one (1) Anderson half per battery, and one (1) on the robot. I’d have to look up the rule number for that, though.

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Actually it looks pretty cool. Of course as a model at this point, we would need to see the actual implementation to inspect. I have seen teams use a number of different 3D printed handles, most using the molded parts of the battery case to clamp the handle to the battery. Most use a threaded fastener to hold the two parts in clamp on the battery. As Jon pointed out the top of the battery does have vent holes under the plastic door. If you leave some space between the top of the battery and the bottom of the handle, you would not interfere with normal venting. Currently there is no rule for battery assy. weight. The only implied limit being the battery cables, 12 inches or less. I bet further iterations could make this device just as functional with about half of the material shown in this drawing. One thing to consider, with a rigid system of fastening the SB connector to the battery, I would expect the SB connector to open with battery vibration.

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In addition to vibration possibly causing intermittent open-circuit events, I am speculating that this may cause (extra) wear on the SB50 contacts.

When my younger son was on a team, we harvested a bunch of battery cables from some old battery assemblies. Many of them needed new cables put on them so we were really re-using the SB50 shells in many instances. When the old cables were removed, I noticed that the silver-coloured plating had worn off most of the contacts leaving copper-colourd patches where the two contacts would normally touch each other. I was going to investigate further but never got around to it.

I love it!

There are push on metal clips that can attach to the finger holes quite firmly.

Steel strap (maybe 1/4" wide) can be run around the battery and make it as well anchored as you want. You could even go over the top or through the handle to take the battery load off the 3DP.

You might want to go to the BIG Anderson for this to increase the mechanical strength.

You do need to plan in something so that vertical acceleration doesnt pop the battery out. The mystery feature might be it…

I’d be curious if the design can be refined to allow for both connectors to be floating so the shocks are a non issue but still have the same effectiveness

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No need to investigate! This is a feature of Anderson Power Poles. They brand it as “flat wiping” but sell it as “self cleaning”. See first point here: https://www.andersonpower.com/content/dam/app/site/resources/techreference/app_pm.pdf

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The manufacturer has an optional handle kit for the connector so it’s not much of a stretch to see it’s still the same connector (in my unofficial opinion and someone who hates scraped knuckles).

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