Best Robot Troubleshooting

[Created by Mike Blazer of San Antonio BEST.  Used with permission.  All copyright reserved.  Please contact original author if you wish to use this information in a context outside of BEST]


Disclaimer: This document is intended to help you, the Best Robot Builder, fix problems with the radio control (R/C) portion of your robot.  This only troubleshoots the ‘standard’ R/C elements of your robot.  The game specific mechanisms are your responsibility.

If you haven't already done so, please read: the Generic Kit Notes, the R/C Transmitter Manual, the speed controller manual, and the battery charger instructions.

General Advice:

bullet Manage you batteries carefully.  Batteries like to work, so they are much happier (meaning, they will provide more energy for your machine) when you use them up before recharging. If you're not using them for a while, then you should discharge them.
bullet Be careful handling small metal parts (screws, nuts, etc.) around the Robot Box.  Any parts dropped on the Robot Box tend to find their way inside and can cause a short circuit.
bullet Solder wire to the microswitches and to the motor terminals (these are among the allowed solder joints).  Wires that are just wrapped around the terminals do not make good electrical contact and will often fall off and/or create a short circuit.
bullet Use electrical tape to insulate all exposed electrical connections.  This will help prevent short circuits.
bullet Before applying power to the machine, take another look at all of your connections to make sure that there are no stray bits of wire or other misplaced metal that can cause a short circuit.
bullet Check that you have fully inserted the servo connectors into the robot box and that the connectors have the proper orientation.
bullet Check that the ribbon connector between the robot box and receiver/tether box is fully inserted in the socket.
bullet Add some strain relief to your wiring.  Use the cable ties provided in the kit, or other methods to protect the wires from being pulled from the terminals, or from bending the terminals and eventually causing a short.
bullet Mount the return kit components on the machine.  You will save yourself some wiring problems and odd behavior by properly mounting the speed controllers, servos, batteries, etc to your machine.  While Velcro is a quick and easy way to mount parts, if you adhere the Velcro to the return parts, you are breaking the rules.  The robot box, receiver box and the speed controllers should already have BEST applied Velcro on them, you may not add to this Velcro, or change the position of the Velcro on these boxes.

Most problems fall into three categories:

  1. Normal operation.  It's not doing what you think it should be doing, but it really is correct.
  2. Setup/Connection problem.  You've made a mistake connecting the R/C components.  These normally don't damage the components, but may blow a fuse.  Double check your wiring against the Generic Kit Notes. Check your solder joints, they should be smooth and shiny, not grainy looking.  Check the crimps on your bullet connectors.  You shouldn't be able to pull the wires out once they have been crimped.
  3. Bad component.  Something actually is broken and in need of replacement from your local kit person.

To solve problems with the R/C setup, you must understand how the system is supposed to work.  Once you understand the system (you get this knowledge by studying the manuals for each of the components and by working with them), it is usually not that difficult to isolate the problem to determine which particular component is not working properly.

Frequently Appearing Symptoms:

  1. Everything is dead.
  2. One channel doesn't work (at all)
  3. A motor attached to the ESC runs continuously
  4. One motor runs slower than the other (both motors use ESCs)
  5. The motor on an ESC hesitates or stalls when going from forward to reverse (or starting out in reverse)
  6. A motor runs backwards (from what you want or expect)
  7. A servo moves the wrong way.

1. Problem:  Everything is dead.


  1. Are the transmitter and On/Off (robot) switches turned on?  Normally, the servos and Electronic Speed Controllers (ESCs) with activate briefly when the robot is turned on.  There should also be some change when the transmitter is turned on.
  2. Check the meter on the transmitter.  It should be move right to the red area to indicate a fully charged battery.  Note: there may be some variation in proper meter indications between different models of transmitters.  When using the Tether Box, the transmitter doesn't need to be turned on as long as you have the single wire connected from the robot box to the appropriate mating connector on the switch-fuse assembly.
  3. Is the battery plugged in? Are you using a charged battery?
  4. Is the power lead from the robot box connected to the pigtail on the switch assembly?  This provides power for the receiver.
  5. Are you using at least one ESC?  Is the small switch on one of the ESC's turned on? The ESCs contains a Battery Elimination Circuit (BEC) that provides power to the receiver.  If the receiver doesn't have power, your machine will not function. The small switch on the ESC turns on the BEC.
  6. Is the fuse blown?  This is a 20 amp fuse and takes a lot to blow it.  If it has blown, check your wiring.  Disconnect the ESC and other components from the ‘Y’ connectors.  Two common problem areas that result in blown fuses are at the motor terminals and the microswitch connections.   These positive/negative connections at these locations are very close to each other.   You need to solder the wires on the outside flats of the contacts, not the insides.  You should not need to wrap the wires around the terminals to get a good mechanical connection.   A good solder joint will support the wire.   Do not stretch the wire to get them to length.

2. Problem: One channel doesn't work (at all)


  1. Have you actually connected to the correct channel connector?  On some robot boxes, it's easy to be off by one connector.  The Channel 1 connector is at the edge of the opening and sometimes hard to see.  The three top connectors (see the Generic Kit Notes, Figure 2) should not be connected to anything.
  2. Make sure all three pins are on, not offset up or down by one.
  3. Do you have the connectors oriented correctly?  With the ribbon connector to the left, the left most wire should be white if you're connecting a servo, or yellow if you're connecting a speed controller.
  4. Does the servo or speed controller (that you had on this channel) work on another channel? If so, then try another servo/ESC on this channel to verify that the problem is with the particular channel and not an intermittent problem with the servo/ESC
  5. Check the pins on the robot box.  The ribbon connector on the side of the box should have 2 rows of pins with none bent.  The 3 pins for each channel should also be free from bends.  (Bent pins usually result from forcing the connectors on or off at an angle.)
  6. Check the ribbon cable connection from the Receiver or Tether Box.  You may not have a good connection unless both of the locking ears are over the ribbon cable connector.  The channel 1 signal is on one end of this connector and would be the most affected if the connector is not plugged in correctly.  The majority of machine problems found on Game Day are the result of not having properly connected the ribbon connector to the Robot Box.
  7. Try using the Tether Box in place of the Receiver Box (or vice versa).  The Robot Box is just a wiring adapter with no active electronics.  The Tether Box has a couple of components that are particularly failure-prone. When one of these components fail, the machine may behave oddly or not at all, when on tether.

3. Problem: A motor attached to the ESC runs continuously


  1. Make sure that your robot battery and transmitter batteries have good power.   The ESC may behave erratically if the power is too low.
  2. Make sure that one of ESC switches is on.  Without the ESC switch on, the receiver has no power, so you have no control signal to the ESC, so it may do all sorts of strange things
  3. If the ESC behaves the same way regardless of which channel it's connect to, then you probably need to adjust the ESC's neutral setting.

The ESCs have a NEUTRAL Setting.  Here's how to adjust it:

  1. Place your robot up on a box so that it doesn't run off the table.
  2. Turn the transmitter and robot on.
  3. Center the joystick and trim controls (on the transmitter) for this channel. If the motor stops running at this point you probably don't need to complete the remaining steps.
  4. Locate the small plastic adjustment tool from the return kit.  Only use the plastic tool for the following operation; metallic screwdrivers can create a short circuit in the ESC and destroy it.
  5. There are two adjustment holes.  Locate the adjustment slot in the NEUTRAL hole.  The adjustment may not be centered in the hole and is difficult to see.  Use a flashlight, if needed, but do not pry up the metal cover plate.
  6. Using the adjustment tool, rotate the adjustment until the motor stops running.  Remember this position
  7. Continue adjusting, in the same direction, until the motor just starts running again.
  8. Finally, rotate the adjustment halfway between this position and the position where the motor initially stopped rotating.   This sets the adjustment in the center of the dead zone.
  9. This motor should now respond correctly to the joystick.
This is the Electronic Speed Controller  (ESC).  Note the large FULL POWER and NEUTRAL adjustments holes.  The smaller hole reveals a LED.  The LED lights up red when driving in forward and green when at full power.

4. Problem:  The motor attached to an ESC doesn't work or is erratic


Does the problem lie in a particular channel, or in the ESC?

  1. Does a servo work when it is connected to the ESC channel?  If it does, then the channel is OK and the problem is either in the ESC or in the motor.  If not, then the channel is bad.  You should be able to get the servo to work on all four channels.  Remember to keep an ESC plugged in and turned on to provide the Receiver power. 
  2. Does the ESC behave the same when it is connected to a different channel?  If so, then you need to check further as described below.

Does the problem lie in the motor or in the ESC?

  1. Test the ESC without a motor.  The LED on ESC should show red as the joystick is moved in one direction.  As the joystick is moved further in the same direction, the LED should change from red to green.  When the LED glows green, the ESC is putting out full power in the forward direction.  The LED does not light up when the joystick is moved in the opposite direction (when the ESC is putting out power for the reverse direction.  If you can't get the ESC's LED to light up both red and green, you should check the FULL POWER setting of the ESC.
  2. Run the motor without an ESC.  To do this, get the battery, switch/fuse assembly and the pigtail (male connector with short wire leads).  Hook up the pigtail to the motor being tested.  (Be careful not to short the leads).  Next hook up the pigtail, switch/fuse and battery.  Turning the switch ON should cause the motor to run.  If not, the motor is bad.
  3. Run the ESC with a different motor.  Hook up a motor that you  know to be good to the ESC (either the large or small motor will do).  You should be able to control this motor.  If you cannot control a known to be good motor on a channel that is known to be good, then the ESC is bad.

5. Problem: One motor runs slower than the other (both motors use ESCs)

Check the Speed adjustment on the ESCs.  The FULL POWER adjustment setting on the ESC and is adjusted in a manner similar to the NEUTRAL settting. Have a look at the ESC instruction sheet for details. Adjust this so that you robot runs in a (more or less) straight path  when if full forward or full reverse.  Also, make sure you have good solder joints and crimps in the wiring to both motors.  A bad crimp or solder joint will add resistance to the wiring, thus wasting power.   If your motors are too mismatched, you should contact your kit coordinator to see if he/she can provide you with a closer matched pair of motors.   Keep in mind that a motor fresh from the manufacturer has a +/- 10 percent acceptable variation in speed.  That means that it's possible to have two perfectly good motors with a 20 percent difference in speed.   You may have to "de-tune" the speed on the fast motor, or get used to the way the machine "pulls" to one side.

5. Problem:  The motor on an ESC hesitates or stalls when going from forward to reverse (or starting out in reverse)


See: SP520+ Electronic Speed Controller Datasheet

This is normal operation.  The ESC are designed to have a short (~1/2 second) delay when going from Forward to Reverse.  This protects the ESCs and motor gear boxes from damage.  This is one of the engineering challenges in the BEST game.  Very often in the ‘real’ world, off-the-shelf products don't do exactly what you need and sometimes they don't even do what they claim (Imagine that!).  Note that the ESCs work better in the forward direction, so it's recommended that you set up the ESCs and motors so that your most critical driving is in the forward direction. In fact, the SP520's are not proportional in reverse; the run at a fixed speed that is roughly 1/4 of the forward speed.

6. Problem: A motor runs backwards (from what you want or expect):


  1. If the motor is connected to the ESC, simply disconnect the bullet connectors and swap the connections.  It's a good idea to mark or record your exact connections.
  2. If the motor is connected to a single microswitch, you'll have to de-solder the wires and swap the connections.
  3. If the motor is connected to a pair of microswitches that reverse the motor direction, you can simply reverse the servo direction for that channel using the reversing switches on the transmitter (see below).

7. Problem:  A servo moves the wrong way.


Use the reversing switch on the transmitter.  This is the only to change the motion of the servos.

Futaba Transmitter Reversing Switches





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Last updated: 10/19/04.