Killer Bees FRC Battery Cart

Teams,
We have had many requests to share this FRC Battery Cart Design,
Our students have created a how-to video, a complete set of drawings, and step by step instructions. Every team needs a good battery cart as part of their competition pit setup. This is a 4th generation design which is easy for any team to build, and a great fall project for your team before the 2021 Season.

One Day Build Video at : Battery Cart Build Video

CAD Model is posted on our team website at KB33 Resources

KB33_Power_Station_Drawings.pdf (691.8 KB)
Battery Cart Build Instructions.pdf (1.7 MB)

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image
The KB33 link led to this page.

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Thank you for sharing this. I love how simple and refined this design is.

We had a design similar to this for many years. It was great.

There are a few things I would recommend adding or refining to this design.

  1. We found that this cart was an excellent way to transport the batteries back to the hotel each night. But getting it loaded into the car was tricky. To help, we added wheels up near the handle and a grab bar down at the bottom on the front face. When we got to the vehicle (assuming you are using an SUV), we would load the cart into the back by tilting the cart back until it was leaning against the back bumper of the SUV. Then we would lift the bottom using the grab bar until the upper wheels were on the floor of the cargo area in the vehicle. At this point, you could just roll the cart into the vehicle and close the hatch. Pulling it out was the reverse process. Without those upper wheels, you end up sliding the cart on the cargo bed which is hard given how heavy it is. Also without the grab bar at the bottom, the ergonomics of lifting the bottom up and letting it back down again was not good.

Edit: I took a closer look at the design and I see that there is already a handle at the bottom (similar to our grab bar).

  1. You want to have a very comfortable handle for rolling the cart out to the vehicle or into the venue from the vehicle. As I said the cart can be heavy with the batteries loaded in it, and a sharp edged handle will quickly dig into your hand making it very painful to pull the cart around.

Edit: Upon closer inspection, I see that this design specifies using a router to round off the edges of the handle. This is very important. Don’t skip this step if you value your hands. We also added soft grip wrap to our handle. This design might be fine without that.

  1. One thing that can help make the cart easier (and safer) to pull around would be to add a “kickstand” type leg off the back with wheels on it. That way, you can tilt the cart back and it will come to rest with 4 wheels on the ground in an orientation that makes it easier to pull or even push if you are on smooth enough floor without risking dropping the cart or needing to support so much weight with your hand through the handle.

  2. We had two instances where the students forgot to plug in the cart and we only discovered it halfway through quals when we were running short on charged batteries. Since the battery cart generally gets relegated to a back, out-of-the-way corner of the pit, we mentors wanted to have a way to check the status of the cart without entering the pit. So, we added an indicator lamp to the main power. It looks like this cart has contemplated that with the power strip and chargers oriented so that the lights are visible, so that should not be a problem with this design. But for teams that are copying this design, make sure you include a way to tell whether the cart is plugged in / powered on.

  3. We integrated the extension cord into the cart so that we would not have to search for a cord to use. We also added a place to attach the coiled up cord when we were transporting the cart.

  4. The top shelf is an obvious place to store the battery tester and provides a nice shelf to set the battery on while testing it. It looks like this design has the power plug sticking out on that shelf. It might be cleaner to have the plug come out the side or back to keep that shelf clean.

  5. I would actually shift all the charging slots down as well as the chargers to make room for a few “cool down” slots at the top. We have found that testing the battery immediately after pulling it off the charger gives a false reading and that you want to give it a chance to cool for 10-15 minutes before testing it. We used the extra slots as cool down slots and having them near the top of the cart is nice so that they are close to the tester (we tied our tester to the cart so that it would not wander off). We added a small dry-erase label area above each of these slots so that the Battery Czar could write down what time the battery was put in the slot. That way, (s)he would know if it had been cooling long enough when (s)he came back later to test the battery. Once it had been tested, (s)he would erase the time and just write “Ready” on the same little white-board area so that if someone from the drive team needed a battery, they would know which one was ready to go even if the Battery Czar was not in the pit.

All of these refinements would be very easy with this design.

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These are great plans Jim! I really like the single-column narrow design. That will squeeze into the pit nicely. I also like how the chargers are visible and accessible from the front.

We went short and wide with ours (limited by the size of our laser cutter), but if I had a redo, I’d follow your plans.

[edit] - the only suggestion I’d make is maybe you can clear some space for a little cabinet above the chargers? We find our storage space is really useful for log books, battery beaks, spill kits, and other doo dads.

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How are the shelves attached to the side plates? We had an older cart where the shelves were screwed into the plywood end grain. It didn’t hold up very long. Did you consider using cross dowels / barrel nuts?

Those are some good ideas. I was thinking it might be cool to combine the wheels from your 1st and 3rd points – have your kickstand long enough and fold up and it seems like one pair of extra wheels could do both jobs.

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Yes, I think that would absolutely work. Real time CD collaboration is so great!

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Hmmmm, one of those I don’t have in my Pokédex! :grin:

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It shows the process in the YT video; wood glue and some nails with a nail gun work very effectively.

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On ours we used a dado to slot the plywood for the shelf to fit in. With a little glue and a few brad nails it has held up for 9 years now. Just one more option to throw out there.

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Jim,
Thanks for sharing. We had mimicked your design in 2015 and had built two carts. They are great! The carts can be top heavy to pull or push when fully loaded with 7 batteries. We are thinking of building a set of 2 small wheels that can be extended away from the cart on the back side to help balance the cart when pushing/pulling it. John
Imgur
Imgur

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John, Those look great, nice work and fast. I am glad you like them.
We have made mockups of kickstands in the past, I have never really liked any of them.
Articulating parts tend to get broken in a device like this.
I am sure that there are many further improvements possible.

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Agree, in an older version that is exactly what I did. More recent versions have focused more on simplicity of method and reduction of tools needed. This makes it more accessible to all to build, regardless of your shop.
The glued on blocks for shelf supports are plenty strong since each only has to support the weight of one battery and there is plenty of shear surface. We have had 2 of these carts in use for about 7 years and have never had a glue joint fail.

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I was hoping to see a picture of it in the first post…oh well, I was able to screen shot from the video to see what it looks like.

Nice cart. We built one that’s even more portable, but holds fewer batteries and chargers, because we’ve found we only really need six batteries, and one triple charger at competitions.

I bet your design could be scaled to make different sizes, to work well for different teams, eh?

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Compact! Very nice. However points are deducted for not naming your batteries after Pokémon. :wink:

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Points should be deducted if you name your batteries after non-electric type Pokémon, and especially if you name them after fire type Pokémon.

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Those wheels are lookin’ pretty slick.

Andy B.

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Just a question for charging. Our setup has the batteries completely horizontal and the cart gets flipped onto its back for moving. At a competition a safety inspector told us to remove batteries and leave then upright on the floor when charging this created a tripping hazard but did not matter because it was better for the batteries? I know its because of some sort of vent thing in the batteries but would the pressure not be released any time the battery is flipped upright. Also these design have the batteries almost horizontal. Any potential issues with those?