• Expansion

    Andre Powell01/09/2022 at 13:15 0 comments

    I've ordered some new wheels for the Rover.
    The present ones only give about 20 mm clearance, which isn't enough really.

    To improve this I've ordered 8 Inch Wheels. This should give approx 150 mm of clearance.

    This wheels however don't have a 5 mm D type shaft connection. However the Roboshop also supplies the appropriate hubs which have 6 mm D shaft holes.
    Amazon provides the appropriate converter and also 6 mm D Shafts.

    The other advantage of this approach is that there is in theory there should be the ability to put a third set of wheels. These would have have either two inboard and one outboard or the other way round.

    A couple of issues, the wheels will take time to get here and there are only three immediately available. Oh well this isn't urgent :).

  • Success

    Andre Powell01/04/2022 at 20:44 0 comments

    I updated the program so that it started off slow and then changed the speed of the PWM.

    This is excellent news ! It means that the project is viable !

    https://vimeo.com/manage/videos/662401812

  • Nudge

    Andre Powell01/03/2022 at 22:14 0 comments

    Today has been of rush as I return to work tomorrow.

    First thing was to investigate why there was a clicking. This turned out to be an accidental short  between the stand offs and one of the power supplies. Easily fixed by cleaning up the tracks with a drill bit.

    Next to re-solder one of the solar cells, now that I have a better soldering iron and tinning agent then turned out a lot better. I then sealed the connections with blobs of glue.

    I looked into how to generate a PWM like signal from the Arduino. I discovered that there is a delay capability down to us. This successfully generated I connected up the system with the Rover stood off the ground.

    Got wheel rotation but forgot to flip the direction of travel for the other side. A couple of line of C and a couple of wires made to connect into the direction input of the Driver.

    Set the Rover down and set it off. Or rather I didn't.

    I switched the current selection to 2 A. While still stationary I was able to get forward movement by a small nudge this looks like it needs to overcome some Sticktion. This might be why there is a 'ramp up' of frequency on Electric motors. I'll look into this after work.

  • Power

    Andre Powell12/30/2021 at 21:15 0 comments

    I have decided on a dual power supply, one for the Motors and their Drives and the other to supply the 'compute' aspects.

    The 12V battery supply will provide for the Motors/Drive and the Lithium P for the compute.

    These supplies need to be distribute and to save space I've created a 'Distribution Stack'.

    This can be seen here.


    Also to save space I've velcro'd the Lithium, the Lead Acid and the Solar Controller together.
    Velcro is useful to tear things apart quickly.


    These can now be connected together. You will note that one lithium battery is different, easy to change and replace because of the velcro.

    You also see that solar cells for the Low Voltage supply connected.
    While I haven't connected the Motors and Drivers up I have successfully connected the RPi and the Arduino boards and powered them up at the same time.
    Not fully tested them but it does mean we are on our way,

  • Drive Train Test

    Andre Powell12/23/2021 at 22:18 0 comments

    After the problem with the last run I diagnosed what the problem was.
    One of the Drivers was set for a fairly high current setting.
    However to avoid the issue again and to be perfectly honest to make things a lot cleaner I took a Vero Strip Board and put some screw terminals on it thus distributing things a better. I also paralleled up the supply lines with wires so it should be able to carry the current.

    I've also created a distribution board for the pulse signalling.

    Both of these boards worked well. Note I kept a constant eye on the power distribution board to make sure.

    I gradually increased the frequency generated by the Sig Gen and got up to 3.2 kHz which gives 120 rpm.
    It worked out well.
    I think there will need to be a separate solar cell for the signal collection and transmission. The reason being that the current spikes due to the Stepper Motors might cause problems for the processors and the LoRa transmission/reception.

    This will be provided by the separate smaller cells and the lithium cells.

    Here is the system running.

    https://vimeo.com/manage/videos/659764156

  • WOOF, WHO LET THE SMOKE OUT, WOOF, WOOF, WOOF

    Andre Powell12/21/2021 at 18:49 1 comment

    Ahhh the joys of full up prototyping.

    3, 2, 1, SMOKE !

    A very jury rigged all four motor with battery, solar cell and sig gen to provide pulses drew a little more current than I was expecting. A thin wire was used in the return path wasn't big enough.

    As soon as enabled the sig gen the wire smoked.
    While not good not terrible. This was part of the learning exercise. As they say no experiment is a failure if you learn something from it.

    So what did I learn.

    1. Have a better prototype Wiring Harness using some form of proper distribution technique.

    2. Dragging a high quantity of Current which is surprising. I was expecting no more than 800 mA.

    This will have an impact on the longevity of a trundling. Well ok ! This is again great as I'm learning new stuff as we go.
    Tomorrow I get some pcb screw terminals which I can mount on some vero board, this will be a better form of distribution capability that screw blocks.

  • Underload

    Andre Powell12/14/2021 at 21:31 0 comments

    I wired up a four batteries and then loaded the stepper motor.
    Max current was 500 mA but it was interesting to with a heavy wheel in motion.

    The wheel is quite heavy so there was an element of gyroscopic effect seen.
    This shouldn't be a problem as the rotation speed should be low.

    https://vimeo.com/manage/videos/656766915

  • Current Versus Frequency

    Andre Powell12/13/2021 at 22:32 0 comments

    I connected up three 3.7 V  1.0 Ah Batteries that had been charged up using the Solar Cells. These went via the battery charger circuit which steps the voltage from each cell to 4 V.
    The sources were placed in Series so the voltage across all three comes up to 12 V.

    Using this I connected the supply to a Stepper Motor Driver.

    Connecting up the  Stepper Motor to the Driver and used a  Signal Generator to provide 5 V Pulse input.

    When the sig gen was enabled Stepper motor rotated.

    This proves that the idea of a Battery charged by Light can rotate a stepper motor.

    I decided to see what the current draw would be for different frequencies.

    Using a DVM set to the 10 A range I was able to get some measurements, unfortunately the resolution was at 10 mA. The next range was maxed out at 200 mA.

    Also this curve has large number of data points missing so the 'curve'  is not to be taken to heart and just an indication.

    I guessed the error bars to be +/- 10 mA.

    The Stepper Motor had no 'Load' but when trying to hold the shaft I could see the current increase.

    Here is the graph.

    The peak current about 480 mA. To make estimations easier let's assume the current draw is 500 mA.

    Assuming that 1.0 Ah batteries and there are three of them this gives a total current capability of 3.0 Ah.

    At 500 mA this give six hours of operation at Maximum current for one motor.
    Note this is at 4 kHz so reasonably fast.

    It will be of interest that to see what happens with two stepper motors. In theory half of the current will be available for each motor so half the torque. This is because Current I understand is related to Torque.

    This could steer the design towards having only two motors. However this removes the ability to turn on the spot and thus aim. Pros and cons.

  • Power

    Andre Powell12/11/2021 at 23:26 0 comments

    I've been doing some back of envelope (I don't smoke so no fag packets) with regards to power.

    I have three sets of Solar Cells, and I've done some measurements and made some calculations.

    Using the SAD lamp as a standard light source for each of the tests.

    Small Solar Cell

    79 mm x 59 mm

    Voltage = 1.59 V

    Current = 35 mA

    Area = 4661 mm2

    Power = 55.6 mW

    Power per mm2 = 11.29 uW/mm2

    Medium Solar Cell

    138 mm x 82 mm

    Voltage = 4.64 V

    Current = 24 mA

    Area = 11316 mm2

    Power = 111 mW

    Power per mm2 = 9.8 uW/mm2

    Large Solar Cell

    149 mm x 130 mm

    Voltage = 5.19 V

    Current = 49.3 mA

    Area = 19370 mm2

    Power per mm2 = 13.165 uW/mm2

    What is interesting is that the Medium Solar Cell is not completely 'active' but the if you just use the 'active' area then the Power per mm2 comes up to 15.41 uW/mm2.

    Unfortunately you can't remove the inactive area, so putting a Solar Cell array has to use the lower ratio.

    Calculations and Assumptions

    Initial idea is to use 6 of the large Solar Cells.

    Using the numbers from the previous analysis we have this

    6 x 130 mm x 149 mm --> 116220 mm2

    This gives 1.53 W @ 5.19 V which gives 294 mA.

    This assumes that the light level of the SAD Lamp not going to be the light level in the field.
    Let it be 50% this brings it down to --> 147 mA.

    The Charging of a battery is not going to be 100% efficient.

    Let's use 75% which gives 110 mA.

    The smallest battery available is 1 AHour.

    Using this it would take approx 9 hours to charge the battery.

    Short Day

    The shortest day is approx 7 hours long.

    Having four 1.1 Ah batteries for longevity and power for Torque.

    To charge the batteries @ 110mA would take 40 Hours.

    This is would be too short even if it's a bright sunny day for the 7 hours on the Shortest Day.

    As there are only 7 hours in which to charge the batteries it has to charge 6 times as fast.

    Assuming the same technology we have to have

    6 x 6 cells --> 36 Solar Cells.

    Physically this gives

    6 x 130 mm -> 780 mm

    6 x 149 mm -> 894 mm

    Effectively it is a 1m by 1 m.

    This would be physically unstable and also would need a large sheet of Perspex.

    Will need to work on the 18 V but this can be solved.

    Once I have this I can look at the batteries again.

  • Charging Test

    Andre Powell12/03/2021 at 18:05 0 comments

    This is a test to see how long using a SAD lamp set to full will take to charge a 1100mA battery.

    Last time I made a measurement of the current output when pointing at the sun I got 60 mA. What we get here we will have to see !