Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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:
http://www.andymark.com/product-p/am-0477.htm

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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!"

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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
:D :D :D :D :D
And the smilies return!

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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...d&productId=10

Re: Where to mount the battery?
 

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

/sarcasm

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

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 irrelevantI 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.

Re: Where to mount the battery?
 

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!

Re: Where to mount the battery?
 

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.

Re: Where to mount the battery?
 

We actually did that last year. It was a pain to change out the batteries when we had back to back matches in eliminations.

Re: Where to mount the battery?
 

Sorry to be a bit off-topic, but why go for this configuration? You'll have very little scrub preventing you to turn, therefore making the robot very hard to drive. Why not just go with the standard kitbot, 6-wheel, dropped centre?

As for the battery mounting, just remember that your battery can be used as a form of "ballast" to move your CoG to somewhere else. Other than that, as long as you can securely mount the battery (using tools such as the Battery Base Mount linked earlier from Andymark) and can access it easily, your battery should be fine as long as it is properly maintained.

P.S. While we're talking about batteries, zip tie the leads. They're the next most likely thing to come lose.

Re: Where to mount the battery?
 

Not to make a grudge, but I dislike zipties and batteries because they are only single use. They can also look bad. I think heat-shrink would be a good choice for what to insulate the wires with. If done correctly, it will hold the wire together with quite some strength. You could possibly hold the battery with the wires (though not the best idea) with the strength if done correctly. Also, does anyone solder the connections to the battery?

Re: Where to mount the battery?
 

Where would you expect such pressure to come from? There's no gas production when a SLA battery is being discharged.

I have no problem with this.

Re: Where to mount the battery?
 

The battery mount should be light, simple, and functional. (Along with everything else on the robot)

When putting the battery in, be sure to secure it well. Ziptie the connectors for the battery to the connector. Use reusable zip ties if you would like.

If you are securing the battery to the robot, make sure it doesn't go anywhere. A few zipties may seem like enough, but if your robot is going over bumps or falling over, a simple strap may be a better option.

A previous poster mentioned holding a battery by the wires. Don't do this. Stress on the battery terminals is a bad thing. Besides for ripping the tab straight off the battery, the performance and safety of the battery will be reduced.

Re: Where to mount the battery?
 

If the choice is between a disposable zip tie and an immobile robot due to the connector coming loose, I think paying the two cents for the zip tie is a good deal.

If your complaint is that they might not look nice, then take the time to make them look as nice as you want.

Huh? Battery wires aren't going to swell or pop from the electron pressure. What are you proposing the heat-shrink tubing would hold the wire together against?

Using heat-shrink on the battery connections is okay. The only problem I would have with it is that it can make checking the quality of the connection difficult.

NO.

NEVER lift a robot battery by its wires. EVER. You'll put stress on the interior connections and risk irrevocable physical damage. But how would heat-shrink affect how strong the wire-to-battery connection is?

That would be a Bad Idea. The amount of heat you'd have to apply to the terminals would be likely to deform the plastic case, and has the potential to warp the plates.

Re: Where to mount the battery?
 

I am superstitious. I prefer my batteries to be upright. The UPS sitting next to me uses the same type battery. One battery of the pair spends its life upside down. Go figure.

While zip tying the anderson connector is a good idea, if it is that loose, one of the connectors are bad. Could be a source of electrical gremlins. Better to strap it some way so that it does not flop around. We put in under the same Velcro strap we use to secure the battery.

We used Velcro tape to secure the battery one year. Bad idea. Very secure. Difficult to change.

Re: Where to mount the battery?
 

Gravity

Re: Where to mount the battery?
 

IFI/VEXpro have a very nice battery cradle as part of their 2013 Drive in a Day Chassis Kit.

Item 217-2966 for US$25, shown at the bottom of this page.



We just picked one up and will almost certainly use it for our 2014 robot.
It is formed out of 1/8" aluminum, so it is very sturdy, but not particularly heavy.

Cheers,
- Dean

Re: Where to mount the battery?
 

That seems like a good battery mount. However, as of what I understand, it is made of Aluminum, so I think it may be a short hazard!

I prefer upright battery mounts because these batteries have a grip that helps you replace them. The battery holder depends on your robot's size/design/CoG. Place it to center your CoG. Also, make it so that replacing the battery is easy. If you can replace the battery within thirty seconds, you have done well! Also, your robot's shape really matters. We didn't really worry about where we placed the battery because we had a very stable robot already. If the robot was like our 2012 robot for rebound rumble, that easily fell over, the battery must have been placed in the bottom center.

This is off topic, but not worth making a thread for:
Many robots won't reach the weight restriction. Are we allowed to place dense materials, like a block of lead or steel, etc. in places on the robot to reduce the CoG?

Re: Where to mount the battery?
 

It is aluminum, but it isn't really a shorting hazard. The lip of the cradle only comes about half-way up the edge of the battery, so it is well clear of the terminals. As long as you follow typical insulation practices and avoid striking the battery with large conductive objects, you should be fine.

Agreed. I like the flat mount where possible since it helps lower the CoG just a bit, but I agree that the mount of choice depends more on the shape of your robot and battery swap access.

I've seen teams do this. As long as there isn't a rule that prohibits it, it would be legal. You'll have to account for the additional material on your bill of materials of course.

Cheers,
- Dean

Re: Where to mount the battery?
 

Better insulate your terminals then--and make sure the battery goes in terminal-side-up. All metal battery holders (which seem to be the vast majority of battery holders...) have that problem. I've not seen too many shorted batteries on metal robots, and I've been doing this for... well, let's not go into how long I've been involved.


My first reaction is to laugh my rear off at that first sentence. Many robots will be OVER the weight limit! Trust me on this. That said, SHOULD you HAPPEN to find yourself underweight, under the 2013 rules (2014 may be different), there was no limit to doing that as long as hazardous materials (like lead) were properly handled. But coming in underweight is akin to finding the Holy Grail (your choice of Monty or Indy to find it).

Re: Where to mount the battery?
 

I'll agree that you can't design the 2014 robot until January, but once kickoff starts, you need to have the battery front and center in your design process.

Key thing is the ability to get to and RAPIDLY change the battery. Nothing is worse than having a battery that takes 10 minutes to change. It should be something you can do with the robot upright. There is nothing more scary or less safe that propping a robot up on saw horses while a roboteer climbs under to replace the battery.

1640 builds custom heat formed boxes every year to hold the battery securely in place. The new mounts that Dean posted would also be a great first pass.

Good luck!

Re: Where to mount the battery?
 

I can see many rookie teams going quite a bit under weight! Since they are new teams, they will typically try to do things as simple as possible!

Re: Where to mount the battery?
 

[laughing myself into a coughing fit] Where do you come up with this stuff?

Re: Where to mount the battery?
 

I'd answer, but 1) I'm on the floor myself and 2) I think the closest approximation is PDOOMA, or SWAG.


Somehow I don't think someone has ever been on or around a rookie team.

Re: Where to mount the battery?
 

Is the battery pressure caused by the stunning visual effects and intense sci-fi action?

Or the 3 word plot summery and wild inaccuracies creating predictably convenient situations? :P

Re: Where to mount the battery?
 

Welcome to Chief Delphi! The community is here to help, and I'd personally be glad to answer any questions you have if you PM me. (Although there are definitely people way more qualified than me here).

A good thread for a rookie team to read would be: http://www.chiefdelphi.com/forums/sh...d.php?t=122662

Now, I wouldn't get too attached to the designs you guys are coming up with (kudos for warming up and getting some practice in though), as no one knows what the game will be, and how it will affect design. When season finally comes though, you'll find that good battery placement should meet the following criteria:

1. Low. CoG is important. You don't want your robot to be tippy.
2. Accessible. Gotta be able to reach and replace it right?
3. Secure. Can't have your power source disconnecting. :o
4. Balanced. (Meaning that in an optimal situation, your battery does not make your robot front or back heavy)

I'm glad you're reading the forums. You'll be able to avoid some of the most common errors.

Good luck during your rookie year!

Re: Where to mount the battery?
 

Not necessarily true. At times, you want the majority of your weight to be on one side of the robot or the other to improve turning performance. Our 2012 robot was completely symmetric, and to be honest, it turned terribly. Just know that moving the battery can effect CG, and you want to use that to your advantage.

Re: Where to mount the battery?
 

If your robot doesn't turn well with its CG in the center, you've got some other problems to address! A frame should definitely be rigid enough and wheelbase short enough to handle a centered CG and turning on a dime.

Not that there aren't reasons for a front or back CG bias, but you should be able to turn without it.

Re: Where to mount the battery?
 

OK,
Time for my annual battery discussion...
The manufacturer says the battery can be used in any orientation except inverted (from the Enersys sheet). While in our service, that is unlikely to cause a problem, leaking may occur if the internal pressure causes the vent to open while inverted.
This type of battery comes in a variety of terminal choices so during manufacture all the batteries are identical and the terminal is soldered into the battery as one of the final steps. If you apply heat to the terminal, or lift the battery by wires attached to the terminal, the solder joint will become intermittent or will fail. I have seen terminals pull out of the battery entirely.
The greatest point of failure on batteries comes from the wire terminal lossening with the battery terminal. Even if you use locking hardware, if the terminals can rotate against each other, the hardware will loosen. I recommend adding a simple #10 external tooth lockwasher between the terminals before you assemble. The teeth will bite into each terminal and prevent any rotation if the hardware stays tight. It also prevents the terminals from "dishing" due to tight hardware. Heatshrink can then be applied to the connection. We use a custom 3/4" heatshrink a company printed for us long ago. With care, a 3" long piece can cover both the wire terminal and the battery terminal. If you can't find or afford that size, electrical tape wrapped around the entire connection leaving no exposed metal is a good alternative. When you insert the mounting hardware, put the nut on the inside of the terminal so that the excess screw length doesn't stick out and produce a nice place to catch a robot structural part. We are a belt and suspenders kind of team so we solder the crimp terminals we use. For battery terminals and #10 wiring, this will require a 50 watt iron (or above) with a large tip. If you use a screw retention terminal (SLU or equivalent), you must strip the wire at least 1/2" or whatever is required for your terminal. If you cannot insert the wire so that strands show beyond the end of the terminal housing, the wire will be pushed out of the terminal after you tighten the wire screw. (Think squeezing one end of a stick of butter or a banana) Again, turn the terminal so that it won't get caught on robot parts when you insert the battery.
Why are all of these precautions needed you ask? The battery supplies all of the current needed for robot drive and control. Any failure that produces a loose connection adds resistance to the power supply. CIM motors draw 130 amps in stall and most teams will use two or four of these. Add a few ohms in a line that draws that much current and heating and voltage drop will result. It may even be enough to cause your robot to reboot or loose connection with the field. A reboot will take up to 20 seconds to recover.
Finally, I don't care how you do it, secure the battery in the robot. I have been pushing for a number of years to disable robots that have the battery leave the robot. It is dangerous, a fire hazard and potentially could leave a trail of toxic chemicals on the field. If nothing else, should you start dragging your battery around by the leads behind your robot, several people will be pointing and laughing. At some point, all robots will tip over, so gravity alone cannot hold in the battery. There are large tywraps available that have a release locking mechanism, however there is no substitute for a wide piece of velcro, belt or mechanical fastening system to keep the battery in place.
Finally, as I mentioned all robot current passes through the battery (primary) wiring. This path includes the breaker, and the input to the Power Distribution board. This path should have the least amount of series resistance as you can manage. Make wire runs short and centered in the robot. Most often, place the PD in the center of your high current loads and position the battery and breaker as needed to keep the run short and provide COG protection.

Re: Where to mount the battery?
 

Putting the nut on the inside conveniently puts the screw head on the outside. You don't want to have your screwdriver/nutdriver shaft running between the battery terminals when you're tightening the connection.

Re: Where to mount the battery?
 

OK, I was asking for this one.

Re: Where to mount the battery?
 

Interesting discussions on CG, stiffness, and chassis… http://www.chiefdelphi.com/forums/sh...ad.php?t=68307

Re: Where to mount the battery?
 

My team has used these for the past few years and have never had a problem with them! The plastic bracket slips into grooves at the top of the battery and holds it very securely. The only thing I would suggest is making sure you have enough clearance to get your hands around the battery to secure the velcro.

Re: Where to mount the battery?
 

Speaking from experience: Whilst pretty particle effects and flying sparks are created, 10/10 would not do again. Keep the nuts on the inside.