DIY Remote Controlled Lawn Mower

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Re: DIY Remote Controlled Lawn Mower

#41  Postby felltoearth » Mar 25, 2020 9:53 am

May be a stupid question but why the 24V power supply if you have to step it down so much?
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Re: DIY Remote Controlled Lawn Mower

#42  Postby theropod_V_2.0 » Mar 25, 2020 10:09 am

felltoearth wrote:May be a stupid question but why the 24V power supply if you have to step it down so much?


No such thing, felltoearth.

The drive motors are used wheelchair units designed to operate at the 24 volt nominal battery voltage. Running them at 12 volts would be possible, but the amperage drain would double and that would shorten the life of the brushes and commutator that feeds the armature windings. The Arduino on-board regulator might be able to accept that high voltage, but it would be right at the upper limit of its tolerance. The easiest way to step down that 24 volts is by using the little solid state LM7805 (5V) regulator for the Arduino and the LD1117 (3.3 V) for the wifi module. Both of those large “transistor” looking devices are cheap and been used for years in these type situations.

The motor drivers (BTS7960B’s) and these regulators will generate some heat at maximum load, and I am seriously considering using a thermistor (a variable resistor that changes value when heated) attached to the large heat sinks incorporated into the motor drivers to switch on a computer cooling fan at some yet to be determined threshold. I have several analog inputs left on the Arduino Nano operating as the “Slave”, and it would be a simple addition to the code to output a signal once that threshold was reached. That Arduino signal would then in turn on an N channel mosFET to drive the fan. The Arduino itself is not capable of driving even a small fan, so this multi step system would have to be implemented. I already have all the parts on hand to do this, but will probably wait until I have tested the drive coding before spending much time on the issue. That fan would also cool the heat sink for the voltage regulators, but I really don’t expect much heat build up in those devices as their loads will be well below their upper limits.

RS

ETA:
Upon giving the power supply issue a little more thought it became clear that supplying the LM7805 with raw 24 volts from the batteries would be pushing its upper limit. In light of this I’ve added a third step down regulator. This third device is an LM7812 12 volt regulator capable of sinking a little over 1 amp, which should be well above the load demanded of the Arduino and wifi module. The LM7812 is more than capable of dropping the 24 volts down so the downstream regulators can operate safely. Considering the heat and rough conditions under which the entire “Slave” will experience I don’t want the electronics stressed by running at their ragged edges.
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Re: DIY Remote Controlled Lawn Mower

#43  Postby theropod_V_2.0 » Apr 06, 2020 11:31 pm

Major issue #1.
Even with the addition of dipole antennae, and upping the output power to maximum, the RF20L01 modules only had a range of 20 feet when in the presence of the running lawn mower engine. Sometimes the indicator LED’s would behave correctly and other times the opposite indicators would light up. There was even a period of time when all four would illuminate at full brightness no matter what input I provided. This would promptly blow up my motor drivers/controllers had they been exposed to such conditions. Worse yet the mower would have gone completely out of control had my tests been on a running mower. Apparently the electrical noise from the mowers ignition system overwhelms the tiny little devices. If I knew more about shielding the wifi receiver, and filtering the ignition noise, I might be able to make my original plan work. As things stand the first effort ended in disappointment.

In an attempt to overcome this problem I have bought a FlySky RC transmitter receiver pair. The receiver will pair with an Arduino Nano and decode the signals into the PWM outputs needed for the motor drivers. This paired system operates at much higher power output and has automatic frequency hopping. The receiver matches the Arduino very well and decoding the signals is much more straightforward than the hoops required to make the RF modules even function.

One big plus with this system is that instead of having to include two libraries for both Arduinos the FlySky receiver only needs one such external code source, and that one is far more simple, with only one micro controller required on the receiver end. Decoding the FlySky signals is far more simple as well. All I need do is sample the signal and convert that to an analog voltage. The Arduino will map the varying signals proportionally, very similar to the stepper motor driven alt/az telescope mount I built, and output the PWM required by the motor drivers. The wiring attachments are also much more simple and can operate on the 5 volts native to the Arduino, so only one 12 volt voltage regulator will be needed. The original design required 3. A 12 volt to step down the 24 volts needed for the motors, 5 volts for the Arduino and finally 3.3 volts for the RF modules. The Arduino can accept regulated 12 volts. I only included the 5 volt regulator as a failsafe to protect that final 3.3 volt regulator in my original design.

I already have the code written for the new setup, and it is far less complex. My new RC system has provision for 4 channels, but only two will be needed to drive the mower. Those left over channels will be used for panic stop, deck height and engine speed. I’m too hard headed to give up once I’ve set my mind to something. I’m confident that a purpose built system will overcome the hacked together el-cheapo solution I first tried.

RS
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Re: DIY Remote Controlled Lawn Mower

#44  Postby theropod_V_2.0 » Apr 16, 2020 10:38 pm

Irony:

I just got out of the shower, and checked my email. Low and behold the second motor driver ordered from China arrived in our post office box today. We are headed out for Jonesboro, AR just a few minutes after the wife gets home from work. I doubt I will be in the mood to hunch over my workbench for a couple weeks after this little trip, thus the irony. I’ve been waiting on this one component to finish the mower side electronics, for months (ordered end of February).

I did solder all the leads from the Arduino and labeled each one with white medical tape (wonder where that came from).
:coffee:

2-5volt positive to the drivers
2-ground wires for the drivers
2-forward (L/R) Pulse Width Modulated outputs
2-reverse (L/R) PWM outputs
4-enable digital output signals (F/R) (L/R) that switch on/off the drivers directionally for each driver
4-analog inputs to the Arduino from the FlySky receiver
1-main regulated power lead to the Arduino with protection diode
1-main ground lead to the Arduino
1-5v lead to RC receiver
1-main ground lead for receiver

(5v supply to all components will be provided by the Arduino on-board regulator).

Maybe by the end of May...

RS
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