Hello All,
Im currently developing a ground vehicle platform designed to accept a wide range of payloads. Im having some issues with [what I believe may be] RF interference or insufficiency. Because im on a budget I used a 72mhz Rx/Tx from a crashed EDF Jet. The issue is that when the UGV is about 100ft away the motors 'twitch' and stop/start. The vehicle is tracked- without any suspension- so there is a fair ammount of vibration on hard surfaces. Im wondering if the 72mhz electronics coupled with the vibration could be the reason for the motor twitch and stop/start. The UGV reacts well when its up on a stand with the tracks off the ground.
I plan to switch to ground frequency- whats the best budget rx/tx kit - Turnigy?
What other interference should I be worried about? [The setup is a cheap 72mhz transmitter/receiver to Sabertooth 2x25 motor controller out to two Dewalt drill motors/gearboxes with Dewalt batteries powering the motor controller. The chassis is cold rolled sheet steel and 6061 aluminum which encases the electronics- the receiver antennae is ran to outside the chassis-wrapped around an aluminum rod as a rigid antennae- for propper line of sight to the transmitter] Should there be a certian 'seperation' of these components to avoid interference at long ranges under vibration?
Summary of questions:
I plan to switch to ground frequency- whats the best budget rx/tx kit - Turnigy?
What other interference should I be worried about?
Should there be a certian 'seperation' of these components to avoid interference at long ranges under vibration?
Could this be another issue all together?
Ryan
Replies
Ryan,
There are so many variables here..But in essence it is probably one of two, either vibration resulting in intermittent contact somewhere, or RF interference.
Try to eliminate the vibration aspect first while keeping the other conditions the same. Drive the vehicle slowly over smooth terrain ( an asphalt car park maybe, or a large smooth grassy area in a park..) at the distance at which you have problems and see if it still occurs. If it does NOT you will have to pursue the vibration aspect..Performing this test with the vehicle suspended , ie, tracks of the ground, is not quite the same - the motors are very lightly loaded and draw low amps, so commutator EMI is much lower.
However, the RF side is more likely - as already mentioned by others, the commutator EMI from those motors is high and capacitors should be fitted across the motor wires AT THE MOTOR, and from each wire to the motor metal case, also at the motor.
The lower the frequency of you RCS system, the worse the interference can be, since the since commutator EMI will diminish in amplitude with increasing frequency.
Then your antenna rod is a problem. First, I trust the aluminium pole is not connected electrically or physically to the metal chassis? If so, this will couple most of the received signal to ground rather than to the RCS antenna wrapped around it. You will lose most of the received signal. Secondly, the RCS RX antenna wire is of a length that is 'tuned' to work best at that frequency. Wrapping it into what is effectively a coil changes that frequency, and also its physical length and thus its RF capture efficiency. It is not always convenient to have the antenna fully stretched out - no space generally, but the straighter, and less obstructed, the better. Wrapping it around any metallic material ( the aluminium rod) however will result in massive signal losses. The rod severely detunes the antenna , increasing it , and results in a poor reception. Non ferrous material will raise the frequency, ferrous material will lower it. If you have to 'wrap' the antenna in order to fit in the space you have , or height available, rather use a plastic tube or fiberglass tube or rod ( plastic electrical conduit or a section of fibreglass fishing rod - NOT carbon fibre-)
Good luck
Joe
The Nampilot
Hi Ryan,
hard to say where the twitching comes from.
For a good Transmitter you might want to look at the Frsky Taranis, way better than Turnigy 9x but slightly more expensive. In my Opinion its worth the money.
Please keep in mind that GPS module and receiver (Telemetry radio and RC receiver as well) should always installed as far apart as possible to avoid disturbing the GPS-reception.
Regards,
Linus
Do you have filter capacitors on the motors? Those Dewalts without capacitors would surely have a negative impact on your RC range.
Frank