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Vorpal The Hexapod User Guide

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Revision as of 05:35, 27 October 2017 by Ehadmin (talk | contribs) (Care of the Servo Motors)

Vorpal Hexapod Quick Links:

General Use Instructions

The Vorpal Hexapod is designed to be used on a flat surface that does not have a great deal of friction. For example: tile, wood, linoleum, a typical table top, industrial carpet.

  • We recommend against running the robot on deep pile carpet, or outdoors on grass or dirt. In these environments the hexapod may get snagged on various items or may collect excessive dirt, dust, or debris.
  • If the robot seems to be struggling to move on a surface with lots of friction, stop running it there and choose another location that is smoother.
  • The hexapod is not water proof and should be kept in a dry location. Never use it in a damp environment, as this may harm the electronics.
  • The hexapod requires rechargeable batteries. Disposable batteries will not work, they cannot output enough current to run the motors properly. See our Vorpal Combat Hexapod Battery Recommendations for more information and for care and handling instructions for the batteries.
  • The hexapod is not built to carry heavy weight or to withstand excessive forces. Do not lean on it, press down on it, or load items on it. It can safely handle three to four ounces (about 100 grams) of items like game attachments and sensors, but this kind of robot is not mean to carry significant loads. Although the servos have metal gears, that doesn't mean you can't break them, the gear teeth are very tiny! See the section below on care of the servo motors for more information.
  • Although it may look like a toy, this is a sophisticated Scratch programmable robot with radio control and sensitive electronics like a microcontroller. Very young children must be cautioned not to lean on it, step on it, throw it, walk it off the edge of a table, or otherwise stress the servo motors or other structural parts.
  • This kit contains small parts is represents a choking hazard for children under 3 years old. It should be used under adult supervision.

Changing the Battery

To choose batteries properly, see Vorpal Combat Hexapod Battery Recommendations.

Here are the steps to change the battery:

  • Turn the Hexapod off using the power switch.
  • Twist the cap counter clockwise (when looking from above) until it comes off.
  • There are red JST connectors tying the battery to the Hexapod's electrical system. Grip the plastic connectors (not the wires!) one side in each hand. Pull apart. Sometimes wiggling them helps get them loose more easily. Never pull via the wires or you may pull the connectors apart internally.
  • Connect a new battery pack (or after recharging the pack you removed) in the same way. Make sure the JST connectors are lined up properly.
  • Place the tabs on the edges of the cap into the matching indentations in the top, push down slightly and turn clockwise.

Turning the Hexapod On and Off

To turn the hexapod on:

  • Turn the dial all the way counter-clockwise, it should be pointing to STP (stop).
  • Press the on/off switch upward (toward the "1" label).
  • Select the mode you want using the dial.

To turn the hexapod off:

  • Press the on/off switch downward (toward the "0" label).

Using the Dial to Select a Function

The dial on the back of the hexapod is used to select between several different functions. Three of the major functions are engraved in the plastic, but some other are available between those three positions.

In order, starting from the extreme counter-clockwise the functions are:

  • STOP In this position the hexapod remains motionless, and the legs never go to sleep. This is useful for checking leg positions in standing position.
  • Adjust. Slightly clockwise of STOP is an unmarked position that puts all servos at postion 90 degrees (out of 180). This means all servo horns should be pointing straight out from the servo. This mode is usually used to set an initial position of the servo horns since it's fairly easy to judge when the horn is coming straight out at a 90 degree angle.
  • Test Servos. Slightly clockwise of Adjust, but before DEMO, is the test servos function. In this mode, each servo will move, in order, from number 0 to number 11. This function is typically used right after plugging in the electrical system, to ensure that all servos are functioning and are plugged into the right ports.
  • DEMO. This is a marked position, and the dial will be pointing straight up. This function causes the hexapod to go through a series of demonstration motions. This is useful for quickly demonstrating the hexapod to your friends, and is also useful for a quick test of all the functions without needing to have your gamepad constructed.
  • BT. The extreme clockwise position is marked BT, and causes the hexapod to respond to Bluetooth commands from the gamepad or from Scratch through the gamepad.

Care of the Servo Motors

Your Vorpal Hexapod is equipped with metal-gear servos that should last a long time with proper care. But they can be damaged if misused, and like all mechanical parts they will eventually wear out and need replacement. This article tells you the main causes of servo failure and steps you can take to get much more life out of your servos.

Causes of Servo Failure

There are three main reasons why servos fail prematurely:

  • Overheating
  • Broken gear teeth
  • Wires broken internally


Overheating causes the insulation in the motor coils to melt, causing the motor to short circuit. If a servo overheats, you may smell a slight "melting plastic" odor. Also, if you touch the servo it may feel quite warm. In extreme cases, if enough of the coils are melted the servo may draw so much power that then entire robot cannot operate because the battery cannot maintain enough voltage to keep the Arduino Nano powered up. Unplugging servos one by one until the robot starts to function again will help find the bad servo.

Overheating is caused either by:

  • continuously moving the hexapod under load with no "rest" for more than 5-10 minutes at a time, or
  • stalling a servo for more than a few seconds. Stalling means the servo is commanded to go to a certain position, but something physically prevents it from getting there, such as an obstacle or another robot during a competition. A few seconds generally won't cause a problem, but continuous stalling will rapidly heat the servo.

Broken gear teeth

Weight stress on the servo can cause one or more gear teeth to break. This is often the case if you hear "chattering" when the servo moves, you are hearing the broken gear teeth meshing and unmeshing.

Wires broken internally

If the wires on the servo get pinched repeatedly, they will eventually break internally (you won't see the break in most cases, it will be hidden by the wire insulation.) A servo with a broken internal wire may work for short periods of time but will stop responding other times.

If you suspect a wire is broken internally, one way to test is to put the hexapod in STOP mode, then slowly move the suspect servo. If it "grabs" and seems to be powered sometimes, but othertimes seems slack, and especially if you can cause this by wiggling the wires, then you almost certainly have an internal break.

It is possible to cut the wires around the break and soldering them back together, but this is actually a lot of trouble and you're probably better off just swapping the servo. For one thing, you don't really know where the break is, so you'd just be guessing.

If you see leg motions that are "pinching" the wire between the servo brackets and legs or chassis, you should stop the robot and adjust the wires so this pinch is less likely to happen.

Recommended Practices For Long Servo Life

Here are some things you should avoid if you want your servos to last a long time:

  • Do not press down on the robot when it is running and the servos are under power. We have seen young children do this, and press with enough force to break several servos in just a few seconds.
  • Along these same lines, when you are installing the cap you need to press down on the robot to get the tabs inserted into their slots properly. But you should support the bottom of the robot with your hand while doing this. You should not press down on the cap to install it in a way that puts pressure on the legs, especially when they're under power.
  • Do not run the hexapod for long periods of time under constant motion. For example, do not enable demo mode with a high capacity battery and let the robot run for more than 5 minutes at a time with no rest. Eventually the servo motors may overheat. For contests and games, make a "round" of play last a maximum of 3 to 5 minutes. Letting the robot rest between strenuous routines will allow the servos to cool.
  • Before using the hexapod, inspect the wires that run from the chassis to the legs. The wires should not be kinked up. There should be enough slack so that the leg can go up and down, back and forth, without pinching or pulling the wires. The leg wires should be going through a slot in the servo bracket, the slot that is above the leg, not the one to the left of the leg.
  • When programming the robot using Scratch X, it is important not to try to lift the entire hexapod body weight with fewer than all six legs from a sitting position.
    • Once standing, as few as 3 legs can hold the robot's weight with no problem. But when initially standing up from a floor position, if you try to lift the robot's entire weight with, say, one or two legs, you will over-stress those servos. Once or twice won't be a problem, but each time may shorten the servo's life.
    • It is safest to write your programs while the robot is on the stand so you don't accidentally do something that will stress the servos. Once your program seems to work on the stand, try it on the floor for real. but if you see the program try to lift the robot's full weight with fewer than all six legs, stop it immediately (or lift it off the floor and put it back on the stand for further debugging).
  • When programming the hexapod using Scratch, it is possible to command two legs to go to positions that cause them to "fight" each other. In other words, they're both trying to occupy the same space at the same time. If allowed to continue for more than a few seconds, this may overheat the servo motors and shorten their life. When running a new program, carefully observe what the legs are doing and stop the program (or turn off the robot) if it appears the legs are colliding.
  • During competitions, stalling a motor may occur when two competitors attack each other, such as during a joust. If the legs of the opposing robots "lock up" for more than a few seconds, the referee should order the players to back off. If they do not (or cannot due to the situation) then the referee should physically separate them, wait 30 seconds for the servos to cool, then continue.
  • Occasionally during competitions, one hexapod's leg may become entangled in the servo wire of the opposing robot. If this occurs, stop the round, untangle the hexapods, and then resume the round. Do not allow contestants to push and pull to try to yank free from the servo wire!
  • Do not attach objects to the hexapod that weigh more than 100 grams (about 4 ounces). This could cause too much stress on the knee servos, and over time will cause their lifespan to be reduced considerably due to overheating. If you design attachments for the hexapod, keep them light!