Best Robot Troubleshooting
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.
- 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.
- 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.
- 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.
- Use electrical tape to insulate all exposed electrical
connections. This will help prevent short circuits.
- 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.
- Check that you have fully inserted the servo connectors into the robot box
and that the connectors have the proper orientation.
- Check that the ribbon connector between the robot box and receiver/tether
box is fully inserted in the socket.
- 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.
- 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:
- Normal operation. It's not doing what you think it should be
doing, but it really is correct.
- 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.
- 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:
- Everything is dead.
- One channel doesn't work (at all)
- A motor attached
to the ESC runs continuously
motor runs slower than the other (both motors use ESCs)
- The motor on an ESC hesitates or
stalls when going from forward to reverse (or starting out in reverse)
- A motor runs backwards (from what you
want or expect)
- A servo moves the wrong way.
1. Problem: Everything is dead.
2. Problem: One channel doesn't
work (at all)
- 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.
- 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.
- Is the battery plugged in? Are you using a charged battery?
- Is the power lead from the robot box connected to the pigtail on the
switch assembly? This provides power for the receiver.
- 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.
- 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.
- 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.
- Make sure all three pins are on, not offset up or down by one.
- 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.
- 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
- 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.)
- 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.
- 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
The ESCs have a NEUTRAL Setting. Here's how to adjust it:
- Make sure that your robot battery and transmitter batteries have good power.
The ESC may behave erratically if the power is too low.
- 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
- 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.
- Place your robot up on a box so that it doesn't run off the table.
- Turn the transmitter and robot on.
- 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.
- 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.
- 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.
- Using the adjustment tool, rotate the adjustment until the motor
stops running. Remember this position
- Continue adjusting, in the same direction, until the motor just starts
- 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.
- 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?
- 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.
- 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?
- 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.
- 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.
- 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
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):
- 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.
- If the motor is connected to a single microswitch, you'll have to
the wires and swap the connections.
- 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.