My new phone

Great value, quality phone with excellent camera

I received this product as part of a review program in return for an unbiased review. Despite being the budget model in the P20 range, the P20 Lite looks and feels expensive. It sits nicely in the hand, light weight yet solidly built. The glossy finish looks great but does attract some finger marks. Initial setup requires a special pin tool to open the drawer that holds the micro SIM card and optional SD card – the tool is included under a flap in the packaging, but isn’t mentioned in the quick start guide, although there are instructions on the back of the phone. Once up and running, the phone is easy to set up, with the included Phone Clone app making it easy to transfer apps and data from another phone. This took under 15 minutes, and was 95% successful, with only a little manual intervention needed. The screen is impressive, with better than HD resolution. It has a distinctive notch at the top that looks very modern, with useful system status information and notifications being displayed on either side of the rear facing camera. There’s plenty of storage, with 64GB of on board memory, plus the ability to add up to 128GB extra via a micro SD card, so plenty of room for apps, photos, video and music. The music playback via the supplied earbuds is clear and powerful, with a surprisingly deep bass response. The earbud lead is fitted with a pause switch, useful if you get a phone call while listening to music. The inbuilt speaker is fine for listening to phone calls but is clearly optimised for voice and doesn’t do so well with music playback. Phone calls are easy to make and clear. However, where this phone really shines is with its photographic abilities, with both front and rear 16MP + 2MP dual cameras. This allows sharp selfies, with a dedicated selfie mode and added ‘beautification’ option. It also allows one of the phone’s party tricks, the ability to log on using face recognition. The main camera features many features – aperture control allows a very fine control of field depth, so it’s easy to have a subject in sharp focus with a blurred background, the ‘bokeh’ effect, also selectable with a dedicated button in portrait mode. Slow motion, time lapse, and downloadable extra features, including a special filter to make photographed food look more appealing, are also included. I’ve only just begun to explore the photographic abilities of this device, and am looking forward to using it regularly, I’ll certainly be taking a lot more photos!

Hexapod robot project – Robotic leg – six of them

I was originally planning to use my own design of parts for this, but having taken the trouble to design them and send them off for quotes for laser cutting and folding, the cost would have been prohibitive, averaging out around £10 per component – and there were 18 components, 3 per leg.

For the initial prototype, it turned out to be much cheaper to use off-the-shelf Chinese components, which brought the cost down to around £40. I bought 18 sets of these pan-tilt servo mounts, nicely made in 2mm aluminium, check out Ali Express for the best deal! They also come with a bag of useful mounting hardware. Each set has a swing bracket and a servo mount.

6 pairs of the swing brackets will be mounted at 90 degrees to each other to give fore-aft movement and the first of two up-down movements.

12 brackets thus need to be cut down to minimise the distance between pivot points, thus reducing the load on the servos. Cutting the first bracket just below the first group of 4 x 3mm and 1 x 8mm holes gives a useful offcut that can then be used as a template for the rest of the marking out and as a drilling guide.

 

The guide template should be bolted to the bracket with a 3mm bolt, see photo for where this bolt needs to go.

It’s a good idea to precisely mark the centre of the 8mm hole as this needs to be accurately cut. Using the servo mount bracket as a template is useful here, as some of the cutouts on this have a 3mm central hole, rather than an 8mm hole. Bolting the 2 parts together as before, then using the central hole to locate a 3mm drill, gives a hole that can then be opened out using a succession of drill sizes – 4, 5, 6, 7 and 8mm in order. Attempting to drill the hole directly with an 8mm drill will be unlikely to give an accurately centred hole, as drill bits tend to wander, especially in thin aluminium.

Once the 12 brackets have been cut down and all the holes drilled, pairs of brackets should be fixed together at 90 degrees using 3 x 3mm pop rivets, using the existing holes. Some filing of the rivets may be needed to clear the servo mounting brackets on either side as they swing past.

And here’s the first prototype arm, complete with servos –  1 down, 5 to go…

I also intend to add ‘legs’ to the end of each arm, a short length of aluminium tubing with a flexible nylon inner part, sprung loaded, to operate limit switches. This is my initial try, but I think that something half this length will work out better!

Note that I have also used these splined metal servo discs in place of the plastic ones supplied with the servos, as they are cheap to buy and give a more accurate fit. They come with 3mm screws, so are easy to fit.

The bracket sets also come with 8mm solid brass bearings with a 3mm bore, I intend to replace these with flanged ball bearings, type F693ZZ, once again ordered from China for around 22p each. Anything that reduces the load on the servos is a worthwhile improvement. I am also awaiting delivery on some servo cable extension leads, so with luck, by the time these parts all arrive, I’ll have finished the other 5 legs and can make a start on connecting everything together and looking at some software design.

Fun with Lubuntu part 2

Well, I’m pleased to say that Lubuntu 16.04, the Long Term Support version of the Linux-based OS installed perfectly on my Dell Mini 9 netbook, with no sign of any screen corruption that I had previously experienced with version 17.10. However, I did avoid the option to download updated software during the installation process; this turned out to be a good move, as we shall see later.

Ethernet connection was immediate and automatic as soon as the cable was plugged in.

Next step was to get WiFi networking to function, turned out to be relatively painless, just went into the Software Updater, found the drivers tab and selected the Broadcomm wireless driver, then selected Update. Took about 10 minutes, but then it was a simple matter to Add a new network connection, supply SSID and password, and it instantly connected.

Final step was to install software updates, so I went ahead and installed everything. It looked to have worked OK, but on rebooting, I had the same screen corruption as I had seen with version 17.10. Clearly something in the updates had broken the screen driver, and I suspected the later kernel was the problem. So, back to square 1 – reinstalled 16.04, set up WiFi as before, but this time, went into the details of the updates that were on offer and unchecked everything that had the word ‘kernel’ in. Installed the rest of the updates and hey presto, everything worked.

I’ll be copying this to the Lubuntu forums as a bug report; however I now have a usable netbook again so worth the aggro.

Resurrecting a Dell Mini 9 netbook (AKA Inspiron 910) (Fun with Lubuntu part1)

As I want to spend a bit more time exploring Linux, I’ve decided to revisit my Dell netbook, which had an obsolete version of Ubuntu as its OS.

Despite being a few years old, I like the netbook’s form factor and build quality, although the highly reflective screen is a nuisance.

I’m planning to update to Lubuntu (//lubuntu.net/downloads/) which is a lightweight version of Ubuntu, designed for older machines with limited resources, as it seems like a good choice, given the very limited resources of the netbook, i.e. 8GB SSD, 2GB Ram. It also has a 16GB SD card, but I don’t want to use that to store the OS.

First attempt, using the latest release of Lubuntu (17.10) didn’t go well – although it worked fine in ‘try before installing’ mode, once the actual install had finished, the screen was corrupted – clearly a screen driver issue.

Restarting after modifying the Linux parameter in GRUB (by pressing the shift key on reboot, followed by the ‘e’ key) to include  ‘nomodeset’ gave an uncorrupted screen, albeit at a lower resolution. Although this proved that it was a video card driver issue, it isn’t a permanent solution, as the changes to GRUB vanished on the next reboot.

Next easy option was to download the LTS version, 16.04 and to see if that works. As this uses an earlier kernel and has been around for a while, maybe it will work better…

Servos part 2 – how to drive them

My eventual aim with this project is to make a hexapod robot. I’m doing it a bit at a time and intend to document my progress here.

Having bought a load of MG996R servos, next challenge is driving them – they take far too much power to be driven directly from an Arduino or Raspberry Pi, so some sort of intermediate control board is called for.

This board

obtained from Ebay for a few pounds has connectors for up to 16 servos and importantly has an input for an external power supply, so that the servos won’t be drawing their current from the controlling device. Control is via I2c serial bus, and boards may be daisy-chained. As each servo is capable of pulling 5-800 mA in normal operation, and 2.5A when stalled, care is required in deciding how many servos can safely be driven from each board – I think 6 is enough, and they will need to be set up so that they don’t stall in normal operation. In order to drive 18 servos, 3 of these boards will be required. Only the data will be carried between boards, not the power – there will be separate power feeds to each board from a stack of Lithium batteries, with 5A polyfuses in case of overload. The power will be controlled by

3 of these DC-DC Buck step-down voltage regulator boards, another Ebay bargain!

It is important to set the output voltage of these boards by adjusting the multi-turn pot. I used an initial input voltage of 10v DC and adjusted the pot for an output of 5.95 v dc. Once this was set, increasing the input voltage to 15v still gave the same output voltage. These controllers are rated up to 5A, and allow an input of up to 38v, so should allow a good choice of battery configurations.

Start of the growing season

The end of January might seem a bit early for planting seeds, but some need as much of a head start as possible – so I’ve planted a dozen seeds of each of 3 varieties of Tomato, one of Aubergines, 2 of Sweet Peppers and 2 of Chilli peppers. This nicely fills up my small electrically heated propagator, which will now sit in my conservatory with the lids on until the first couple of leaves appear.

Servos, particularly the cheap ones from Ebay

Tower Pro servos
 Tower Pro are a well regarded Taiwanese manufacturer, see their website at :
 
Home Page
They sell their products via their international distributor for specific regions of the world. However, as far as I know, they don’t sell via Ebay. There are a number of businesses based in China that are selling servos that carry the Tower Pro brand, via Ebay and other sources, at low prices. Carefully examine the images on the real Tower Pro website and compare them. Are these genuine Tower Pro servos? Draw your own conclusions!
 Nevertheless, because they are so cheap, they are useful for projects such as robotics. Personally, I wouldn’t use them in anything that flies, as their reliability is an unknown quantity, particularly regarding motor longevity- but you do get some well proven electronics, a powerful motor and metal gears, pretty good for the money. They have a few problems, though, and can be improved.

Note that there are a number of different variations on the Chinese manufactured servos, mine were purchased in 2018. There doesn't seem to be any difference internally between the MG995 and MG996R servos that I bought, apart from the labels.

 !! Undertake these modifications at your own risk. Some of the work is very fiddly, using very small components. Please don’t blame me if you wreck your servo !!

 1) Dismantling
 Remove the 4 screws holding the case together. Lift off the upper case and remove the gears. Remove case bottom. Using pliers, carefully grip the motor and ease it from the casing. Take care not to squash the motor can!
 2) Gently tilt pcb forwards to gain access to the 2 tabs that secure the square feedback potentiometer into place in the outer case. Ease these tabs apart with a very small screwdriver while gently pressing on the Pot Shaft. The entire assembly should drop free from the case.

3) Note that the 3 chips on the board are:
 a) AA51880 servo controller – see datasheet for full circuit details
 b) DTM4955 Mosfet dual ‘P’ channel
 c) DTM9925 Mosfet dual ‘N’ channel
 The feedback pot is 5K linear (mine measures as 3.6K)
 The 2 Mosfets are arranged in H-bridge configuration to drive the servo motor.
 4) 2 components on the circuit board need replacement, as the ‘dead zone’, as supplied, is too wide, making the servos very unresponsive. Change them to the values specified in the AA51880 chip datasheet.

R3 should be 1k; C4 should be 100nF(0.1uF); both type 603 SMD parts - These 2 components determine the ‘dead zone’ for the servo arm.

No idea what the supplied capacitor is, but the resistor is a 2k2.

Also add a 100nf disc ceramic capacitor across the motor terminals to reduce motor noise and interference



5) The 2 sleeve bearings (brass at the top, nylon at the bottom) on the output shaft should be replaced by 6 x 10 x 2.5mm roller bearings.

 
6) Thanks to Jfitter for the original info – see his post at //www.rcgroups.com/forums/showthread.php?2485803-Fixup-MG996R-servos

First Post

So, here’s the start of my blog. Created with WordPress, hosted by 000webhost.com via FreeHostingNoAds.net. Initially my posts will be experimental, trying out what WordPress has to offer, so won’t be of much interest to anyone, but hope to be posting some useful content soon.