One tachometer is required for each Rotor, to monitor and control the rotational speed of the rotors. The second tacho will be required only if a second Rotor is installed. The first one has been built and operates satisfactorily. It uses a Picaxe 29X2 Micro as an I2C slave. The micro uses the "Count" command, to count pulses for 2 seconds from one of the Hall Effect sensor OpAmps on the Direct Drive PCB. The speed of the rotor is measured in Meters Per Second. The display is made from 3 x 1" Common Cathode 7 Segment LEDs. These are driven by 3 UDN2981 Darlington Source Drivers and decoded by 3 4511 BCD to 7 segment decoders. The Picaxe has a command "bintoascii" which uses the output of the "count" word variable and then puts the integers of the units, tens, hundreds, thousands, and ten thousands into 5 variables. Each of these is then sent as a binary code to the 4511 decoder. The thousand and ten thousand digits are included in the program
, but not used in this application. The display has a decimal point permanently set on and the count is manipulated so the readout has a resolution of 0.2 MPS with a max reading of 99.8 MPS.
For my programming I prefer to use the BASIC language, and this is one of the main reasons for using the Picaxe system. In case there is a need to change to a non bootloader system, using the same chips as now, I have changed from the "bintoascii" command to using the "rem" remainder function. This is compatible with the two BASIC systems I am considering, Great Cow Basic (free) and PicBasic Pro 3 (paid), and appears to compile ok on both, and works on the Picaxe. Apr2016.
The micro outputs 8 codes using 3 output pins. These codes are utilized by the guide wheels and stabilizers at startup and shutdown, and the rotor speed control and emergency overspeed shutdown. The codes sent represent ranges of values. All this is handled by a 40 pin Picaxe for each Rotor. This has been changed to sending the actual value via I2C serial and is converted to codes where required. Apr2016.
At present (Sep 2015) the system is set to start and run up to maximum speed. I see a
need to have each Rotor reach Idling Speed, and when both Rotors are Idling then a manual switch will allow both Rotors to go to Running speed simultaneously, with neither allowed to be more than 5% from the other. Incorporated into this arrangement is a means of adjusting the max rotor speed temporarily while each Rotor is at Running speed.