Battle Hardening the Inside of Your Bot

Posted in Uncategorized by Near Chaos Robotics on April 12, 2015 No Comments yet

When most people are designing and building their bot they focus on the armor, weapon, and drive system. Making sure these are all in good order is important, but there is something that is often overlooked: The internal systems. A good number of knockouts at robot events aren’t due to catastrophic damage, but due to a single small failure at an inconvenient location. Many of these failures can be avoided by doing what is often referred to as “Battle Hardening”.

Cover Your Exposed Receiver Plugs

Small receiver wrapped with electrical tape.

Most 2.4ghz receivers use a bind plug to put the rx in bind mode. This is done by connecting the signal and negative leads of the Batt/Bind port on the rx. If your rx has exposed prongs for these ports it is possible for conductive material to contact these plugs during a match, putting your rx into bind mode. Your bot will stop moving and in all probability, and there are only two was to get the bot out of bind mode- power cycle the receiver, or bind to it. The first isn’t doable during a match and the second may well take longer than the 10 seconds you’ve got before you’re counted out. This can be avoided by wrapping the exposed prongs with electrical tape. It’s a quick, nearly weightless way to minimize the chances of this ending your match.

Wrap Your Connectors

Wrapping your plugs with tape absorbs shock.

Most common connector types (Deans, JST, Powerpole, etc…) feel like they plug in pretty securely, and really, they do. However, robot combat is a rough sport and there’s a good chance your bot will see some serious forces in the arena. These forces, when experienced at the proper angle and in the right order can be enough to unplug your connectors. A quick wrap of electrical tape is typically enough to absorb the initial shock of the impact and keep your connections together.

Restrain Your Wires

Restraining your wires will help ensure your robot doesn't eat its wires.

Another potential danger caused by the shock of combat (or just putting the top armor on your bot) is that the wires might find their way to a moving component. When this happens, there are a few potential results: You could have the thing its touching grind/rub away at the insulation until the bare wire is now in direct contact with your chassis, you could have it cut the wire, or you could end up with it grabbing hold of the wire and trying to pull it free of its connections, along with anything that’s tangled up with it. None of these are good, and taking a bit of time to tie down your wires now can save hours of rewiring at an event.

Tape or Shrink Wrap Your Exposed Connectors

A bit of well placed shrink wrap can prevent shorts.

This part is pretty simple, the less exposed metal that’s part of the electrical system of your robot, the better off you’ll be. Exposed connections mean you’re at risk of a short, and a short likely means you’ve burnt up something expensive.

Pad Your Batteries

A little foam can save a lot of problems.

Batteries are relatively fragile things, LiPo batteries to an even greater extent. You should take care to minimize the shock that gets transmitted to your batteries. Rigid mounting is a recipe for damaged cells or a battery fire. When dealing with LiPo batteries, one thing I’ve found that helps greatly with their longevity is to put them in a padded foam enclosure. This allows the packs to swell while under heavy draw without reaching any solid barriers and gives them the best chances of survival.

Use Loctite – Seriously, Use It!

If you’ve got bolts going somewhere that you never want to get out, use red Loctite. If you might want to get them out some time in the future, use blue Loctite. If you’re removing them after every fight to get to parts, you can probably skip the loctite, but make sure they’re nice and secure before each match.

Use Connectors On Parts You’ll Potentially Need to Replace

Just about every connection uses a polarized plug.

When doing the wiring for your bot, it may add a bit of cost and a tiny amount of weight to the system but it’s typically worth it to have each element of your system able to be removed and replaced without soldering. Use polarized (ie Deans) connectors wherever possible to minimize the risk of reversing the polarity on a critical system. Use bullet connectors on parts where you’d potentially need to reverse the polarity quickly. (Typically spare drive motors)

Have A Common Power Distribution Point

For both the positive and negative leads coming from the battery, have a single point where the power is transferred to the rest of the robot. Typically, the positive portion of this will be on the far side of the power switch from the battery. For the negative side I tend to prefer high current connectors bolted together and wrapped in tape. These distribution points should be placed as close to the battery connection as is practical in your robot as that will keep the peak current in most of the wires in your robot as low as possible. Lower current means less heat, and less heat means less risk of meltdown. It also means you can use smaller gauge wire throughout the rest of your system as it doesn’t need to handle as much power which can reduce weight.

Practice Soldering

There aren’t many ways to build a bot without soldering somewhere, which means you’ll want to ensure you’ve got strong solder connections. There are a few keys to strong solder connections: The correct solder, the correct iron, good solder flow, and keeping the iron/heat in place long enough that you’ve got the connection reasonably covered. There are plenty of opinions on what is “right” so I’ll leave it at what I use, which has proven to be good enough for bots ranging from 150g to 30lbs for quite a long time.

Solder: Solder with Rosin Flux Core
I bought a spool of this in 2010 and still have plenty left.

Soldering Iron: Weller W60P 60Watts/120V Controlled Output Soldering Iron
This iron with the widest tip I could find has worked very well for me. Weller CT5D8 tip

Getting good flow with flux: Lucky Bob’s Acid Flux
This stuff’s a bit nasty and you’ll want to make sure you burn it all off when you’re using it or else it may corrode your wire over time, but it’s part of the recipe for a strong connection. The process I use is: Brush acid flux on bare wire, coat tip of iron in rosin cored 60/40 solder, touch coated iron tip to wire on all sides.

Helping hands to avoid charring your fingers: Something like this
I tend to not use them, but these are a huge help while you build up a tolerance for hot wires.

Battle Hardening Small Motors

http://www.teamrollingthunder.com/Kitbots/Battle_Harden/body_battle_harden.html

Pete Smith wrote up a guide to battle hardening the Kitbots 1000rpm motors. These techniques can be applied to all similarly designed gearboxes with minimal modification.

Thanks for reading, if you’ve got questions or requests for future articles send me an email at MikeNCR@gmail.com or post it over here: http://sparc.tools/forum/index.php?topic=5.0