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Vorpal The Hexapod Troubleshooting Guide

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Vorpal Hexapod Quick Links:

Applicability: Gigapod, Megapod, and Hexapod

This trouble shooting guide applies to all three sizes of our hexapod project, because all three use very similar electronics, and all three use the same exact gamepad design and software.

Hexapod does not work in STOP, TEST, or DEMO Modes

If the hexapod does not move as expected in the three standalone modes (STOP, TEST, DEMO on the dial) then the most likely problem is a wiring issue, however there are some other possibilities.

Wiring issues

Let's discuss wiring first. A jumper wire could be disconnected, connected to the wrong pin, or could be loose and not making a firm connection. Check your wiring against the instructions diagrams to make sure they're all on the right pins. Second, check to see that each connector grasps the pin it's connected to firmly. It should not just fall off the pin. It should require at least a little bit of tugging to get the connector off the pin. Gravity alone or gentle shaking shouldn't make it come loose. If you find a connector that won't grasp its pin firmly, you can usually fix it by setting the connector housing on your table such that the little metal tab that shows through the plastic housing is face up, then push on that metal tab with your hex key. Use one to two pounds of force, moderate force. Then try it again on the pin. If it still is loose, try again with a little more force. If that still doesn't work, then use a different wire (your kit comes with extras).

Now, assuming you've checked all the wiring and the robot still fails to operate in the stand-alone modes, some other possibilities are discussed in the subsections below.

These subsections assume you've turned the dial to STOP then turned on the power switch, and the robot does not spring to life and stand up. The servos may slightly twitch or may not move at all.

Lights appear on Nano and Bluetooth module, buzzer beeps on startup, but servos do not move

If you self-sourced parts, the most common cause of this is that you did not place a shunt between VCC and V+ on the servo driver module. Failing to tie those two pins together (you can use a short jumper if you don't have a shunt) means the servos get no power. (The kits we provide all have the shunt pre-installed, but you might just take a look to be sure it didn't come off.)

Another possible cause (whether you self-sourced or not) is the SDA/SCL pins on the servo driver might be reversed, not connected to the correct nano pins, or the wires could be bad (loose connectors).

Rarely, there could be a bad servo driver and you'd have to contact support@vorpalrobotics.com to arrange for a replacement.

No lights are visible on the Nano, Bluetooth module, or Servo Driver

If you have no lights at all on any component, here are the likely causes:

  • Battery dead. Make sure you are using charged batteries.
  • One or both batteries are inserted backwards. Batteries must both be inserted so that the negative (-) side of the battery is on the side of the holder with the spring, and the positive (+) is on the side that is flat. If you inserted just one of the two backwards, things will be ok as long as you correct the situation. If you inserted both backwards, however, you have most likely destroyed the entire electrical system, including the BEC, the Nano, and possibly the servo driver and bluetooth module. Contact customer support at support@vorpalrobotics.com.
  • Batteries are not fully inserted. It's not uncommon for friction to cause the positive side of the battery not to make good contact with the flat terminal of the battery holder. There can be a small gap between the battery terminal and the battery holder. Just push with your fingers, starting at the spring side toward the flat side of the battery holder to make sure there is good contact.
  • Bad switch or BEC. You may have a bad switch or bad BEC. This is not common but it's possible. Contact customer support: support@vorpalrobotics.com

Lights are showing on the Nano, Bluetooth module, and Servo Driver but buzzer does not sound during boot

Assuming wiring is confirmed good, this issue is likely to be that the Nano has lost its program stored in flash memory. This can happen because of static electricity during assembly. It is usually possible to fix this just by reflashing the Nano. Instructions for doing this are here: [Vorpal The Hexapod Arduino Setup Guide].

You only need to flash the robot Nano. If you are unable to flash the Nano (for example you are sure you set the TOOLS/PORT menu in the IDE correctly but you get "not in sync" errors) then the Nano itself may be defective, possibly due to static discharge. In that case contact customer support support@vorpalrobotics.com

Hexapod Constantly Beeps in All Three Of STOP, DEMO, and RC Mode

If the Hexapod constantly beeps in all three of these modes: STOP, DEMO, RC, then the issue is almost always that the Servo Driver is not connected properly. The robot's nano attempts to talk to the servo driver, but nothing comes back. So the Nano will beep then attempt to reboot the servo driver. But that doesn't work (because wiring is bad) so the cycle repeats, causing a nonstop beeping sound.

Check the SDA/SCL wires going to the Servo Driver. They could be swapped, or one or both of those wires might not have a good grip on the pin (on either or both of the servo driver and Nano sides of the connection).

Rarely, this can also be a bad servo driver board. Contact customer (support AT vorpalrobotics.com) support if you're sure the wiring is good and you still have this issue.

Hexapod Works in Demo Mode but in RC Mode it constantly beeps and won't respond to gamepad

This issue is almost always caused by bad wiring between the robot's HC05 Bluetooth module and the robot's Arduino Nano.

There are several different ways the wiring can be bad:

  1. TX and RX and reversed or otherwise misconnected.
  2. TX and/or RX pins on HC05 are using a jumper wire that is loose. Sometimes you'll get a jumper that doesn't hold tightly to a pin. This lack of holding could be either on the HC05 pin or on the corresponding Nano pin. If the wire basically falls off if you just shake the module, then it's too loose. You can either tighten it by pressing on the connector with the hex key, or you can just swap the wire with a spare that's not too loose.

Servos Can't Lift Hexapod or are Sluggish


  • Vorpal can't stand up at all, servos seem to struggle.

Possible causes include:

  • Batteries are low or dead. Recharge the batteries. It is also possible that you have batteries that are just no good. Cheap no-name brand batteries often vastly overstate their capabilities.
  • Improper surface: Vorpal is designed to work on reasonably smooth surfaces such as tile floor, wood floor, smooth table top, desk top, etc. It will not work on most carpets. There are "carpet feet" being developed by some Makers which may solve this in the future.
  • Too much friction on servo bearing. Make sure your 3D printed models are cleaned up, especially the little hemisphere on each servo mount on the chassis, and also the little hemispherical hole in the leg hinges. This hemisphere is the bearing opposite the servo shaft, and if it has drips or other defects there may be too much friction for the servos to move smoothly. Sandpaper any areas that look misshapen or rough, or put a drop of silicone grease on the hemisphere. (Other types of oil will also work, or even petroleum jelly, but be careful and apply with a Q-tip or paper towel very carefully, because some kinds of oil may eat through electronics).
  • Legs out of adjustment. If the legs are adjusted such that Vorpal "rides too low" then the amount of torque required to walk increases and the legs may not be able to keep up with the requirements of the walking gait selected. Put the robot in ADJ mode (turn the dial fully counterclockwise to STOP, then slightly clockwise until the knees go out straight). Now, it's not always possible to make the servo horns come out totally straight from the body due to the way servo horns are manufactured. But, if you can't make it come out 90 degrees straight, it's better for the horn to be a little too clockwise than to be a little too counterclockwise. Too clockwise will make the leg lift the robot body a tiny bit higher, which is fine, but too much counterclockwise will make the robot ride "low" and stress the servos more.
  • Bad servo. If one or more servos are bad, the other servos may struggle to lift the robot's weight fast enough to keep up while walking. If a servo is obviously bad (chattering excessively, twitching, not moving at all, or clearly not pulling its fair share of the load) then that's the probable culprit.
  • Bad BEC. It is possible for the BEC (which is on the battery/switch assembly and provides 5V regulated power to the robot) to go bad if it gets overheated too many times, and in this case it may not be able to output enough amps to keep the legs moving properly. This is the least likely cause, please eliminate other causes before requesting new hardware.

One Servo Doesn't Work

Most likely causes include:

  • The servo has gotten unplugged from the servo controller. Open up the hexapod by removing the screws holding down the electronics caddy and check the wiring.
  • The servo has a frozen gear. Occasionally when a servo goes to its maximum position it may get stuck there. You will know this is true if the servo won't move easily even with power off. You can usually fix this by turning power OFF, then gently applying pressure to the servo in the direction you would expect it to move until it "unsticks". If the same servo keeps getting stuck, you should replace it.
  • The servo has gone bad (either gears are broken or wiring is damaged). There are several possible causes for this, but in any case the only fix is to replace the servo.

One Servo Jitters Constantly

It is normal for there to be some humming sounds while the robot stands as the servos activate and deactivate to maintain the standing posture. But very loud chattering or large twitching motions are not normal.

  • This typically means the servo has gone bad and its electronics are not responding properly. First check to make sure the servo's wire is completely inserted in the servo controller, but if that looks ok the only fix is to swap the servo.

Hexapod works at first, but loses height while walking, and/or hip servos lose home position

This problem is called the "drifting servo" problem and it was identified in early 2018 as a type of defective servo that our prior testing procedures did not detect. We received a batch of servos in late 2017 where a percentage of them have this problem. If you bought a kit from us between October 2017 and January 2018, you may have this issue. Also, if you did not buy the servos from us, you have a very high probability of having this issue as many defective servos are sold by online sources such as Aliexpress, Ebay, Banggood, etc.

The symptoms are:

  • In either demo mode or RC mode, the robot starts up and seems to be working at first.
  • Within 30 seconds to 1 minute, the robot starts "losing height". The knees drift so it gets lower and lower until it is "crawling" on the ground or can't move at all.
  • Another related issue is that hip servos may lose home position such that they do not return to neutral, and this gets worse and worse until legs start crashing into each other. If allowed to continue the crashing legs will overheat and then burn out.

The only fix is to replace the bad servos. You will need to determine how many servos are bad, then (if you bought the kit or servos from Vorpal Robotics in late 2017 or early 2018) send email to support@vorpalrobotics.com and report how many replacement servos you need. Also give us enough information to find your account on Kickstarter, Indiegogo, or our Vorpal Robotics Store depending on where you purchased the kit. (If you did not purchase the servos or kit from us, you need to get new servos from whatever vendor sold them to you.)

Here is a procedure for determining how many servos have this issue:

  • Leave the hexapod off for at least 10 minutes. The drifting servo problem occurs as the servos heat up during use so we want them to be room temperature to start.
  • Turn the dial to STOP, then turn the robot on. The legs should now go to the normal standing position. Very slowly turn the dial clockwise until the legs go into ADJUST mode, where the knees come out straight from the robot body.
  • Observe the position of the knee servos. Confirm that they're all coming straight out from the robot body. Make a note of any that are slightly high or slightly low.
  • While still holding the robot in the air, turn the dial to DEMO mode. Let the robot run through two or three demo cycles (a cycle ends with a pause of several seconds).
  • Turn the dial all the way counterclockwise again to STOP mode, then slowly turn clockwise into ADJUST mode again.
  • Write down on a piece of paper any servos that are now obviously too high. For knee servos, make sure you write down the LARGER of the two numbers on the leg.
  • Keep observing the robot for a minute or so. You should see the ones that are too high slowly move back down into neutral position as they cool. This would confirm that those servos do have this issue.

Repeat the above procedure to find any hip servos (the ones attached to the main body) that drift. In the case of hip servos, you do not need to use ADJUST mode since they are always at 90 degrees in STAND mode. Observe how many of them do not return to 90 degrees after running DEMO mode. Again, remember you need to start from a cool robot so turn it off for a few minutes before testing.

Replace any servos that have the issue. If you purchased the servos from us and you are still within the six month warranty period we will replace them without charge, just send email to support@vorpalrobotics.com.

Gamepad D-PAD Buttons Perform Incorrect Functions

For example, the backwards button makes the robot turn around in circles, the left button makes it walk forward, etc. This is almost always because the D-PAD module you have doesn't match the current firmware settings in the Gamepad.

This can almost always be fixed by a simple procedure:

  1. Turn off the gamepad.
  2. Hold down the SPECIAL D-PAD button (the one all the way at the top, above the four directional buttons). Keep holding it.
  3. Turn on the gamepad while still holding the SPECIAL button.
  4. Count slowly to ten, then release the D-PAD button and try out the robot to test.

This procedure tells the gamepad to try and auto-detect the type of D-PAD signals coming in. Once detected, the gamepad will store this information in nonvolatile memory (EEPROM) so you should not have to do this again unless you physically swap out the D-PAD hardware.

If this procedure does not fix your issue, contact our support email: support AT vorpalrobotics.com.

Hexapod Works in Demo Mode but in RC Mode it always walks forward even when no buttons are pressed

There are two possible problems here:

  1. The connections between the Gamepad Nano and D-PAD are disconnected, loose, or incorrect. This will cause the Gamepad to think you're pressing the "Walk forward" button the D-PAD. Check for loose or misconnected wires. Sometimes you'll get a jumper wire that doesn't hold well on the Nano or D-PAD pins, in that case swap to a spare jumper, or alternatively press on the little metal bit showing through the plastic Dupont housing with the hex key to tighten up the connector.
  2. You may have a bad D-PAD. If you did not purchase the D-PAD from Vorpal Robotics, we have seen there are vendors out there who are selling defective D-PAD modules that look exactly like the ones we sell, but they have faulty electrical signals. You can check this by monitoring the output of the Gamepad using the Arduino IDE Serial Monitor. For more information on how to do this, see our wiki article Vorpal The Hexapod Arduino Setup Guide.

Hexapod Works in Demo Mode but stands motionless in response to gamepad

First, make sure the hexapod works as expected for STOP, TST, and DEMO dial modes. If it doesn't work in those modes, it isn't going to work with the gamepad either!

Next, check the following:

  • Make sure the battery is charged in the gamepad and in the robot.
  • Make sure the hexapod dial has been turned to RC (remote control mode).
  • Make sure the gamepad is turned on and you see lights through the little holes in the cover.

If you see lights through the holes in the center of the cover, observe the blinking pattern. Here's what the blinks mean:

  • NOT CONNECTED: When the Bluetooth modules are not connected, there will be a fast, steady blink.
  • IN THE PROCESS OF CONNECTING: When they first start to connect, they will blink slowly at first, then will go dark for a couple of seconds. This process will only take about 5 seconds.
  • CONNECTED: When they are properly connected, then there will be a 2 second pause followed by two quick blinks, and this will repeat over and over as long as there is a connection.

The next few sections explain what to do in each of these situations.

Lights indicate connection is good, but robot not responding

This could be because you've not hooked up the wires properly on the Bluetooth module, either the one on the robot or the one on the gamepad. Carefully check connections.

Another common cause of this is that the gamepad Nano has lost its program. This can occur due to static electricity during assembly. In most cases you can simply reflash the gamepad code onto the Nano and that will fix it. Instructions for flashing the Nano are here: [Vorpal The Hexapod Arduino Setup Guide]. Note: you only need to flash the Gamepad in this case, since the robot works in demo mode that means the robot Nano is fine. If you are unable to flash the nano and get "failed to sync" messages that probably means your Nano is fried, contact customer support: support@vorpalrobotics.com

Finally, there could be a general issue with the gamepad, such as buttons not working. Loading the Arduino IDE (as instructed in the prior paragraph) will allow you to go into DEBUG mode and get data out of the gamepad to see what might be wrong. Use the Arduino serial monitor to see if button presses result in output from the gamepad.

Lights never show a connection

If the Bluetooth modules are not paired after about 10 seconds (two quick blinks followed by 2 seconds dark means they're connected properly), then the possible issues are:

  • Make sure both the robot and the gamepad bluetooth modules have lights.
  • Make sure the GND wire on the nano in the gamepad is properly connected. For example, if you accidentally connected it to something like RST then the nano will have lights and appear to be working, and the Bluetooth modules can even connect to each other, but in reality the Nano is constantly resetting itself and never running the program.
  • If you have several hexapods, make sure you're using the correct gamepad that's matched with your hexapod. If need be, open up the gamepad and the hexapod and check the labels on the Bluetooth modules, make sure the labels match. If the labels are different, the two modules won't auto-pair and connect. You may have mixed up modules when building several robots.
  • To get further information, flash the gamepad with the DEBUG version of the gamepad firmware and see if the messages are correct. See the article Debugging Gamepad Issues for more information.

No lights at all

If you do not see any lights at all in the center of the gamepad, then:

  • The gamepad battery may be low or dead.
  • Your Bluetooth module may not be getting power, check wiring, especially the VCC and GND connections. Make sure jumper wires do not fall loosely off the pins, if they do you should swap to a new jumper wire or press on the little plastic tab on the connector with the hex key to tighten up the wire.

Hexapod Only Works a Short Time Even When Batteries Fully Charged

The hexapod may only work for a few seconds or a few minutes when with proper batteries it should work for nearly two hours. This is almost always because you have used 18650 batteries that have a very aggressive "protection" circuit that cuts them off when power surges as servo motors all come on at the same time. Some 18650 batteries will strictly limit current in this way because they are meant for low current applications.

We strongly recommend EBL 3000 mAh "white top" batteries. See Vorpal The Hexapod Battery Recommendations.

Hexapod Legs Don't All Touch the Ground in STOP Mode

If the legs are out of adjustment, you may use TRIM mode to adjust them. See Vorpal The Hexapod Trim Mode Guide.

Vorpal The Hexapod Quick Links

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