One of the more attractive options for those who are looking to buy a retractable landing gear is to invest into Tarot TL65B44 set. It is a rather reliable landing gear and performed well in numerous crashes. Even though it is called "small" the height allows to operate significant camera gimbal setups, such as HobbyKing Brushless ActionCam Gimbal.

Of course, the most straightforward method of use for this gimbal is to connect the servo leads to a receiver or a flight controller. Nevertheless, not many flight controllers at this point of time allow for sonar driven landing gear. In this article we are going to look at how to operate Tarot TL65B44 by means of the Arduino Pro Mini board and HC-SR04 sonar unit.

Arduino Pro Mini is an ATMEGA328p based. For the purpose of this article we'll consider a 5V, 16MHz version.

Of course, we aim at a practical utilization of the relatively cheap components. HC-SR04 Sonar Unit is a rather inexpensive solution for distance sensing. With some workarounds on the programmatic level it can reliably perform up to 2.5m. These units are normally equipped with 4 signal interface pins: 2 are used to supply 5VDC of power, while the other 2 are trigger and output signal (echo).

You can select several methods of assembly. I have successfully connected both units including the electronic interface and indicator LED on a prototyping board.The entire setup fits into DIY B70x41x23mm New Black Plastic Project Box Electronic Case with some simple cutouts for a solder-on pin connector, sonar unit, serial interface of the Arduino and the LED indicator.

In the following drawing you can see the schematics of electrical connections. Pay attention to pin routing between the Arduino Pro Mini board and the sonar unit.

A couple of comments on the code. It uses 2 libraries: Servo.h (part of the standard Arduino IDE installation), Average.h (has to be downloaded from here). Parameters:

• trigger_altitude - Trigger altitude in centimeters. It is important to keep in mind that this sonar module does not operate reliably in altitudes above 2.5m
• CNT 10 - the size of floating array used for mode function (averaging procedure). If the size of this array is increased, the averaging procedure will smoothen the analogue sonar input more. However, this would come at a cost of the greater latency and longer initialising delay
• attemptsL - a number of times a low enough altitude value shall be registered in order to set the landing gear down (false positive check)
• attemptsTO - a number of times a high enough altitude value shall be registered in order to retract the landing gear (false negative check)
• CutOffDist - an extra filter to avoid the registering of extreme values (any value that is higher than CutOffDist won't be registered into the floating array)

Files:

Sonar Driven Tarot TL65B44 Landing Gear Version 2.2 2.2 HOT	(1 vote)
The original file has been upgraded to Version 2.2. This version uses a better averaging algorithm, as well as introduced a lengthy pause to perform gear retract manouver. All parameters are still adjustable, so you are more than welcome to make your changes. Please post your comments and advise of possible bugs/improvements.
GNU/GPL  2016-02-19  2.34 KB  728	Download

Feel free to download the file. We shall appreciate if any developments to this project were advised to us, so that this article could contain the relevant links and updates.