Frequently Asked Questions

General Questions

1. How do I apply for a kit?

Follow the instructions on the Contact us page.

2. We have taken part in previous competitions and already have a robot or kit, can we take part in this year's competition?


Robot Questions

1. I am hearing a high pitched whine from the circuit boards, what's wrong?

This is normal and is caused by the high frequency electronic Pulse Wave Modulation circuit (PWM). The whine should stop when both transmitter controls are central (in the dead band). You can therefore use this sound to get the two trims exactly in the correct position.

2. When I switch on the transmitter the wheels turn, what's wrong?

Move the trim adjusters next to the control sticks to their central positions. If the wheels are still turning slowly adjust the trims until the wheels stop and the normal whine from the drive boards ceases. You should only need to move the trims a few clicks. One trim will stop both wheels turning in the same direction. The other trim will stop the wheels turning in opposite directions.

3. What can I do, the red light on the circuit boards keeps coming on and my Chariot moves forward in a series of jerks. This is particularly noticeable when turning.

This is normally caused by the voltage falling below the value needed to drive the circuit boards when you demand full power. Check the batteries are fully charged. The voltage should be at least 18 volts. There may also be a high resistance in the power leads. Check the crimp connectors. Are they firmly attached to the wires? Are the wires broken and only attached by a single strand of wire?

4. Why I am getting very erratic response to control movements even though the motors appear to be turning?

Check that the wheels are still firmly attached to the axles and the locking screw has not fallen out or broken.

5. Why does my Robot make a horrible clicking sound when starting off and reversing?

A. Check that the Torque ring at the front of the drill motor is turned fully clockwise (maximum) viewed from the wheel end.
B. We have also found that after some use the motor and gearbox screws can vibrate loose. Remove the top plastic drill casing to expose the motor. Check the motor is still firmly attached to the gearbox. If not, take out the motor and gearbox, select the torque ring to Minimum torque. Remove the three gearbox screws. Separate the motor from the gearbox (small central pinion will come out of gearbox. Tighten the two small screws attaching the motor to the gearbox plate. (Put a drop of superglue on the threads before reinserting them) Replace the motor and gearbox plate. Insert the three gearbox screws (with a drop of superglue). Replace the motor and gearbox in the lower plastic casing and refit the top plastic casing.

6. Why do my batteries break loose when I am playing football?

The velcro battery fixing is not strong enough if you insist on playing "Robot Wars". Devise a stronger way to attach the batteries to the chassis. You were supplied with two long cable ties.

7. My chariot wheels spin when I try to turn and it keeps getting stranded with the drive wheels spinning when it crosses the join in two floor boards.

This is probably the result of tyre wear. On a flat board the Chariot should rock on the drive wheels such that there is a 4mm to 6mm gap under one balancing wheel whilst the other is touching the ground. You can adjust the height of the balancing wheels (i.e. move them upwards) by elongating the 10mm fixing holes in the sides of the MDF chassis with a round file. Note during two weeks continuous operation at the Edinburgh Science Festival the drive wheels lost 10mm in diameter. Tyre wear on tarmac will be much greater than that.

8. Why do I have trouble mounting the see-saw when I approach from the left?

This is because of the diagonal drive configuration which causes the two drive wheels to lift off the ground. If you approach the ramp either straight, or from the right, you will have no problem.

9. Our tyres are wearing down, where can we get replacements?

Tyre wear is a known effect, particularly if you operate the chariot on a rough surface such as tarmac and do lots of spins on the spot. During the 2007 Edinburgh Science festival the tyre diameter decreased by 5mm over the two weeks of continuous operation!

For competitions we find that wear is an advantage as slick tyres seem to give more grip especially for the pushing events. (as Formula 1 motor racing).

There are three disadvantages though:

  1. It needs slightly more power to turn and the battery charge does not last quite so long as before.
  2. You need to raise the idler (balancing) wheels to maintain good traction.
  3. Aesthetic looks

It might look slightly better if all the wheels are slicks and you can easily swap the idler and drive wheels over. To do this you need to drill a transverse hole in the idler wheels hub to take the 4mm bolt which attaches the nylon wheel hub to the aluminium axle adapter.

We get the wheels from Machine Mart.

Wiring up & Testing

1. My chariot goes OK in a straight line, but it won't turn?

More power is needed to turn than to go in a straight line. Check your batteries are fully charged.

2. My chariot goes fast forward and back, but is very sluggish turning. What can I do?

Check the plugs are inserted in the correct channel numbers on the receiver. The Chariot requires more power to turn than to go in a straight line and the PIC software is designed to allow this.

3. Why, when going at high speed, won't my Chariot turn?

Check the plugs are inserted in the correct channel numbers on the receiver. At full forward speed (Channel 2) the PIC allows extra power from channel 4 to be added to the appropriate wheel to allow it to speed up for turning.

4. If I connect the battery directly to the motors they go faster than when selecting full speed through the drive board.

The power available through the drive boards is limited for four reasons:

  • To allow turning at high speed (The appropriate motor turns faster when you select full forward power AND full turning power).
  • To limit the forward speed to a sensible value that will not cause serious injury. A Rampaging Chariot weighing 12kg travelling at 20 mph can break your leg!
  • A normal electric drill can only be reversed when stationary. You can select full reverse speed on your Rampaging Chariot when it is travelling forward at full speed. The gearboxes are not designed to take these huge loads and to limit the shock loads on the motor gearbox and extend its life to more than a few minutes, we reduce the forward power to a sensible limit.
  • To let the batteries last a reasonable period of time.

5. Should the aerial be straight up?

Yes the aerial should be straight and vertical for best performance and range, but at the distances you normally control the Rampaging Chariot we find it is acceptable to loop the aerial over, provided you keep it well away from the motors and control boards which are sources of electromagnetic interference.

6. Can I shorten the aerial?

The aerial has to be exactly the length supplied for best performance and range. We don't recommend shortening it at all.

7. I can't trim my transmitter to get my Chariot moving forward and backwards in a straight line, even when the batteries are fully charged.

A. This could be caused by a high resistance in the main power leads. Check the crimp connectors. Are they firmly attached to the wires? Are the wires broken and only attached by a single strand of wire?
B. This symptom could rarely be caused by one drill motor being more efficient than the other in one direction. One solution is to reduce the power of one motor by a small electrical resistance or a mechanical friction brake. A further way is to angle the wheels in the chassis. Failing all else use extra skill when reversing.

8. Does the Rampaging Chariot have Fail Safes in both channels?

The Rampaging Chariot motor control boards incorporate fail-safe software which checks that the radio signals in both channels are within normal limits. If either channel goes outside these limits the system is programmed to switch off both motors. This satisfies the rules of the Robotic Games.
We do not guarantee that the system will switch the motors off under every failure condition, or under certain radio interference conditions. This is why you must always treat the robot as live whenever the batteries are connected and take the safety precautions described in this booklet. Rampaging Chariots are powerful robots that can bite.

9. Why does my robot not work if I plug a standard servo into a spare receiver channel?

The receiver is powered from the master motor control board. The voltage regulators on this board are only designed to supply 100mA which is insufficient to drive an extra servo, Either plug a separate battery into the receiver or change the 5V and 12V regulators on the master board to MC7805CT and MC7812CT which are capable of supplying 1 Amp.

10. Can I operate my Rampaging Chariot from one control stick?

If you unplug the channel 4 lead from the receiver and insert it in the channel 1 slot you can control the Rampaging Chariot from the right stick only. You can use any combination of channels that suit your style.

11. Can I use different motors in the same chassis?

No, different motors rotate at different speeds and have different gearbox ratios. This will give you some terrible control characteristics.

12. Will I damage the batteries if I leave them on overnight?

Yes, if you overcharge the batteries they will get very hot and this can cause serious damage to both the battery cells and the charger. We recommend that you stop charging when the battery temperature reaches 40 degrees C. Depending on the state of charge at the start, a full charge can take about 4 hours. You can use a time clock if you want to charge the batteries overnight.

Circuit Boards

1. Will the halogen test light always illuminate if there is a fault?

No the test light in series with the battery will only indicate a major fault with the MOSFETS, though it will limit the current to the board and stop major damage to the components.

2. Does the 10 ohm resister or the two voltage regulators heat up under normal operation?

No these components never heat up unless there is a fault on the board. The 10 ohm resister acts as a sort of slow fuse. If you feel or smell the resister heating up, disconnect the battery and investigate for shorts I always put my fingers on top of this resistor and the 12v and 5v regulators when I first apply power to a board and quickly remove power if I feel any heat. If the resistor heats up you most likely have a solder bridge across two tracks. This could be as thin as a human hair. If both voltage regulators also get hot the fault is likely to be around the PIC IC. If the 5v regulator is cool and the 12v regulator is hot, the fault is likely to be on the 12v side around the driver IC.

3. How do I know which way round to insert the control leads?

The plugs on the leads going to the receiver are keyed and should only go in one way round unless you apply some force. If in doubt, the black wire should be at the end of the receiver. The 3 pin plug in the centre of the left side of the circuit board has no keying and the socket is inserted with the black wire to the edge of the board.

4. Why does the red LED illuminate when I demand full power or a turn?

Probably because when you demand a large power the battery voltage drops below that required to operate the PIC. Check the battery and charge it up.

5. Why does My Chariot suddenly jerk when running normally for no apparent reason?

This is normally caused by poor radio reception or interference. It could be caused by another chariot operating on an adjacent frequency or by sparking from the motors. Sparking can be reduced by cleaning carbon from the motor commutator by running the motor at constant speed for a minute with the wheels off the ground.

6. Why does my Chariot suddenly move for no apparent reason when my transmitter is off?

Due to the pseudo failsafe programming the receiver must have received a valid radio signal. This could be interference from a robot operating on an adjacent frequency. You must always treat your robot as live when power is connected and never leave the power on when not required.

7. Why am I measuring 5 volts on the first regulator and 3.5 volts on the second?

If the regulators are not heating up because of a short, you probably have a 5v regulator in the 12v position.

8. The Red LED is on and won't go out?

This indicates that a valid signal is not being received. Check the master/slave jumper is in the correct position. Check the plugs are inserted the right way round (black lead to edge of board). Check the radio leads are inserted in the correct colour sequence. Check for a strand of radio lead wire shorting across the top of the board.

9. I connected the battery the wrong way round. Will it have done any damage?

The main electronics are protected via a diode which should prevent damage to the ICs. The MOSFETS are not protected and the full current from the battery will pass through the MOSFET protection diodes. This current could be up to 50 amps and may blow the diodes. Particularly on the 2006 model boards which have 50A MOSFETS (2007 model boards have 175A MOSFETS). If the diodes are blown, the board will probably still work for a short while, but the first time you command a full power reversal, such as when playing football, the reverse voltage generated will blow the driver chip. Kaput.

10. I put the PIC in the wrong way round. Will it have done any damage?

You may be as lucky as me and realise your error before it heats up too much.

11. I put the driver chip in the wrong way round. Will it have done any damage?

I don't know, but don't recommend you try it as this is the most expensive component on the board.

12. The LED is giving the correct green indications and the motor turns forward, but the test bulb lights up when I select reverse.

The fault is with one side of the MOSFET bridge. Either a MOSFET is blown or there is a short across a track, or the diode is the wrong way round, or the heat sink is shorting. It is possible that the driver IC is blown caused by a previous problem such as the battery terminals being connected the wrong way round in the past. Check for a solder bridge, remove the heat sink and retest without it fitted. (this is OK with the test bulb in the circuit). If the problem is still present stick it in a jiffy bag and send it to me.

13. Can I interchange motor drive boards between 2006 model Chariots and 2007 model Chariots?

The motor drive boards have different PIC programmes, but are functionally the same and can normally be interchanged if you also change over the PIC.
The 2006 model motors rotate at 600 RPM whereas the 2007 models have different motors and gearboxes and rotate at 900 RPM. As the top speed of the 2007 model was far too high for the size of arena we use and caused a lot of unnecessary gearbox strain and commutator arcing, we have adjusted the PIC programme to compensate.
You can freely swap the 'slave' boards between models without changing over the PIC, but if you swap a 'master' board you should also swap the PICs. Take great care not to bend the pins.