Where to mount the battery?

Technical Electrical
1

Hey all. Digby Baker-Porazinski from team 5236. This is my (our) first post in CD, so everything I say will probably be in some way some sort of taboo.
This probably isn’t even in the right section.

Anyway.

This is our first robot of our first year of competing. Design is coming along smoothely, but we’ve hit our first roadblock: where to mount the battery. We agreed it should be low to keep the center of gravity low (the thing’s 14 pounds) and situated in the rear to counterweigh the game mechanism, whatever that may be. But the battery is large and cumbersome, and we’re having trouble deciding where to safely and efficiently place it.
That being said, any tips or examples of where you’ve put your battery in previous years would be much appreciated.

Thanks from Man o’ War, team 5236, Cambridge, NY.

2

Exactly what are you designing for? The FRC build season doesn’t start until Kickoff (first Saturday of January), so I assume a preseason warmup bot?

Rule of thumb: Low and to the center, with a container made to prevent the battery from sliding around your robot. For 11, this often means bent 16GA Aluminum, but Beta used 8020 and polycarb to build their battery box. Doesn’t really matter as long as it doesn’t slide around and doesn’t fall off.

3

I really don’t want to come across as attacking in your first post - I’m just trying to help. But… the main difficulty I think you guys are going to run into is that it’s against the rules to start robot design before the build season starts. Besides that, we aren’t even sure what size the robots will be yet, which game piece we’re using, how we will interact with them, if the field will have any obstacles, etc. I’m not saying it’s useless to be thinking about this stuff before Kickoff, but just know that you can’t get a jump ahead of anyone by doing “pre-design” or pre-building.

Lots of teams do CAD before the season, in the form of design exercises or practice, including our team. But using any design made before the season starts without changing it is illegal. It’s okay to come up with an idea for a drive base and then CAD it, but you can’t use that design when the season starts without changing it in some way. On 2791 we usually come up with a concept, then change details once the game comes out (e.g. the size of the frame, exact gearbox layout, etc).

As for a good place for the battery, you want it as low as you can and in a place that you can reasonably get to. It is more important that the main breaker be easy to access than it is for the battery to be, but you still don’t want students to have trouble changing it fairly quickly. Stowing the battery vertically in some sort of custom box is a good way to save on space and to make removal easy. Put it off to one side if you have a heavy manipulator on the other side, otherwise try to bring it a little closer to the center.

We don’t usually decide exactly where the battery goes before we have an idea of where our manipulator is going to be. We don’t want to put it somewhere, and then make students have to reach in / out / around a bunch of parts just to get a hold of it.

4

The other important thing to keep in mind is that you will be changing the battery every match. The battery needs to easily replaced in the pits.

One option from AndyMark:

our demo bot just has four blocks screwed to the belly pan and a Velcro strap (battery should not fall out if robot is tipped). Also, be careful of sharp metal brackets which might crack the battery during a robot collision.

5

Low is good however I wouldn’t necessarily assume the game mechanism will be in the front or back. You could counter weight it with your drive motors however. 4 CIMs is 11lbs plus 2x gearboxes closer the opposite side as the battery could work. Also accessibility is key. And consider how you will get to the power connecter.

6

I noticed that you were a 5*** team, so, Welcome to the CD! Over here, you will be able to find tips on everything you are wondering! Here is a good thread on getting started

OK. Now, back on topic!
So if I am not misunderstanding you, your team is wondering where to mount the battery. There is no specific place to mount the battery. However, make sure that is is easily accessible and doesn’t come in the way. Last year (2013), we built a battery cradle, fastened to the side of the robot. This was outside the robot, so the battery was very accessible. The cradle was lined with some foam weather seal, to secure the battery. And just to make sure no one was scared, we put a strap of velcro to hold the battery in place.

Try to keep the battery leads short. You may find it helpful to place the breaker near the battery. That will help with the engineering of the electrical system.

Keep the battery very low. Since it is so heavy, it will allow you to lower your CoG (Center of Gravity)

How large is your team? If it is large enough, you really need to create an electrical team. Our (Team 1165’s) electrical team is two people because we don’t have much for them to do!

“MAKE SURE THE BATTERY DOESN’T FALL OUT”, as Magnets says!

Try to keep your design as simple as possible.

Make a DemoBot before the season starts, if you have the components and time. That way, you will know how to connect things together in your actual robot.

That was a long post. Anyways, good luck and enjoy the “sport of the mind!”

7

Welcome to CD!

In the past our team has used a variety of different ways to mount and secure our battery. We usually build an aluminum box around the battery so it doesn’t wiggle or move around.Then to secure the battery in the box we use seatbelt material.

The first year (2011) we used seatbelt material we sewed velcro onto it, worked quite well until we has some accidental discharge and the rivets pulled out of the seatbelt.

In 2012 we learned from the discharge and used the seatbelt material as well as a cobra buckle instead of the velcro. We also doubled up and reinforced the rivets holding the belt.

Last year we went back to velcro but the name brand stuff. We again used the seatbelt and just used one continuous piece around the whole battery box so we could eliminate the weak point of the rivets.

Overall if there is any doubt in your mind about it coming out or breaking the holder the battery is seated in, it can never hurt to reinforce it more. Also make sure it is easy to release the battery and take out. You don’t want to be dealing with zip ties or complicated systems if you have a quick back to back match.

8

Haha: Just to get complicated, and this isn’t for you!, What about an automatic battery loading mechanism to automatically switch the battery and charge the battery?!?!

Oh yeah! Also, the robot docks in, connects to the tether to the DS, so that the programmers can get tweakin’ right away! Also, a 120AMP PSU to power the robot without the battery! The robot should dock on to get these features!

Next, you have a robot cart with vision tracking so that it can drive itself! Avoid the crowd and just follow a person. Better would be to build a powerful quadcopter to
:smiley: :smiley: :smiley: :smiley: :smiley:
And the smilies return!

9

Welcome to CD. You made a good choice by asking here, since we love to help. And I am sure you understand that using anyhting designed before the season starts is against the rules. Sorry.

For the battery:
Low is good. Protected is good too.

Accessible is critical. You change batteries very often. But make sure no matter what it won’t come out (including upside down robots…)

Make absolutely positively certain that the battery terminals cannot touch any ANY metal robot parts. If it does, “Flash, Bang, Send for Help” is sure to happen.

The wires from the battery, through the main circult breaker, to the power distribution board, should all be as short as possible. These wires are heavy, and you do lose power in them, so shorter is better. This means, location should consider other parts.

The orientation of the battery in the robot is NOT important - flat, upright, even upside down are all OK. (Upright for charging though).

Last, if you have a spare week or three, search “Battery” on Chief Delphi and read all the posts from the last decade. You will truly be an expert if you do that.

Good luck in the season, and post often.

10

However you decide to mount it, make sure you use foam. It will reduce the vibrations that the battery experiences. You don’t want the internal plates touching each other (or any of the other bad things that can happen to a battery). Strap in or otherwise contain your battery as well. Your robot will wind up in an orientation you don’t expect.

Battery orientation (flat or standing up) doesn’t matter as long as it’s not upside down.

Otherwise, what everyone else said applies. Low, contributing to a balanced COG, short wires that don’t get pinched and mounted in a way that makes it easy to change batteries quickly.

I recommend using 90º aluminum angle to make your battery mount. It’s the perfect shape, strong, light and easy to interface with your other structure.

Here’s the battery mount from our 2012 robot. It uses angle on 3 sides with a strap and foam to contain the battery. It tipped over on the field several times without issue.

BatteryMount.jpg
BatteryMount.jpg918×637 426 KB



BatteryMount.jpg
BatteryMount.jpg918×637 426 KB

11

SECURE THE BATTERY! You don’t want the battery to break and leak acid all over your bionic machine!

12

A picture is worth a thousand words… Can you post a proposed design picture? Are you 4 wheel drive? 6? This will weigh ( :rolleyes: ) in on your placement of the battery as well.

In addition to the posts above, I have some additional considerations. Please also remember this is some general guidance and is not the solution.

You do not necessarily want your CG (Center of Gravity) in the center of your robot, as this is not ideal for a 6wd robot or a 4 wheel drive “narrow” chassis. In the case of a 6WD robot, placing your CG on the rear half may be beneficial in your design, as it is really just a 4wd wide chassis with pair of “extra wheels” up front (NOTE: This is an oversimplification).

For a narrow 4WD, placing the CG towards the rear wheels and adding something like an omni wheel on the front will allow you to rotate the robot easier, as a 4WD narrow tank-style/differential drive bot is difficult to turn due to scrub force.

13

Expanding on the above post about how drive choice relates to battery placement, if you chose to do mecanum (which I don’t necessarily recommend as a rookie) CG (and therefore battery placement) becomes much more critical. All in all though, if you are a rookie team with no ridiculous manufacturing resources and little experience, I would just go with the kit chassis, a plywood bellypan and the 3-pieces-of-angle + velcro strap battery holder mentioned earlier.

14

Thank all of you for your input.

WMarshall11: We’re just troubleshooting. Nothing is in legitimate design or construction yet, we just saw the weight of the battery online and decided to try and tackle the issue before it arises. I appreciate the help.

Chris is me: I appreciate the info. Worry not, there’s no official CAD designing going on yet, we just downloaded a 6-wheel STEP file to examine.

gpetilli: Thanks for the link. We’re thinking aluminum with slots, where we’ll implement velcro straps. We hadn’t taken sharp objects fully into consideration, so that’s a good wake-up call.

jman4747: Thanks for the alternate options. Depending on what happens come Kickoff day, we may well need a plan B.

Yash101: Wow. That was very helpful information. Sadly, I doubt we’ll get a functioning electrical team going, considering that our team consists mainly of 5 POE students, but it’s a useful idea. The link was also very helpful.

Ice.berg: Thank you for your input. We had been considering what sort of fastener/strap we could use, and the different material examples are helpful.

DonRotolo: Again, nothing’s really being designed, but I appreciate the heads-up. Thank you for the info, it helps more than you know.

cgmv123: Thanks. Your design seems cost effective and deceptively simple. I also appreciate the visual provided by your photo.

Stinglikeabee: That’s very helpful. Our design will likely be 6 wheel, omnis in front and back.

MetalJacket: Sounds good. Definitely not Mecanum, we’re nowhere near ready for that. We’re thinking 6 wheel, omnis in front and back.

Again, thanks to everyone for your support.

15

One option you could look at is using the eStop Robotics Battery Base product. Many teams use it and I’ve never heard of a team losing a battery during a match while using it - https://www.estoprobotics.com/estore/index.php?_a=viewProd&productId=10

16

Mount the battery underneath the robot. It is pretty fun to deal with.

/sarcasm

17

The battery is capable of 600 amps fully charged, even a 100 amp 12 volt power supply will not be enough to get four motors turning.

Please NO!!!

Please be sure to insulate the terminals at all times, whether on or off the robot, in a box or not. 600 amps is capable of welding metal.

18

Actually, even upside down is perfectly fine. Just do not charge it upside down, because of the overpressure vents on top. During use the battery won’t need to vent making orientation irrelevant

I have seen several robots with the battery mounted right to the bottom center of the robot. To change the battery, they just tip the robot on its side, exposng the battery mount.

19

It really is too early to start “planning” on where the battery will go. There has been some great advice on here, but keep in mind that every game is different! For example, if you were climbing the tower this past year, depending on design you might not have wanted your CG to be in the middle of the robot… battery placement for many teams might have been a key component of getting the robot to hang correctly!

As others have alluded to, there could also be obstacles on the field or other rules that affect how you build your robot. For example, in BreakAway bumpers had to be fairly high, and pretty much every team used a riser kit to elevate the frame off the floor. This potentially gave you significant space underneath your main frame to put stuff!

As for location of your main mechanism, We’ve had ours all over the place! Our rookie year, we had mechanisms on the front and back of the robot. Over the years, we’ve built two “fork-lift” style elevators, where one was on the front and one was on the back. In BreakAway, we even had a mechanism that was primarily on the side of the robot!

When designing a robot, you really need to look at the entire thing. You can’t design part here, part there, and mash it together and get something good. There’s a lot of give and take as you build it up, a lot of planning that goes into making sure you have room for everything where you need it. If you want to practice for the next few weeks before kickoff, take last year’s game/rules, and design a robot for that!

20

I’d be concerned with the pressure on the vents from sustained inversion. Erring on the side of caution when it comes to batteries is a good principle.