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Scaled-up Solar Tracker – proof of concept part 2

see part 1 :: see part 3

Pole top mount design

I’ve completed the design of the mount for the pole top and have asked a local supplier to make the parts for me out of stainless steel.

sketch showing the pole-top mount design
sketch of the pole top mount being used to angle the solar panels depending on time of year
Detail of the pole-top mount design
click images to see larger in new tab / window

As you can see from the sketches, the design of the pole top mount allows the solar panel frame to be pointed further up or down, depending on the time of year.

Continuing the build…

Here’s the starting point for part 2 of the build

photo showing the starting point for part 2 of the design and build
starting point for part 2 of the design and build

The parts I was waiting for arrived:

  • the stainless steel pole
  • the lifter bearing – the short length of bar with the recess for the ball bearings that the lifting eyelets attach to
  • the 1:810 reduction ratio gearbox

The installation went smoothly – I used grease to hold the ball bearings in place while putting the lifter bearing in place.

I’ve now realised there’s a slight issue there as regards portability. It’s because the only thing stopping the bearings falling out (apart from the grease) is the bottom of the pole resting on them. And if the pole is to be removed for easy portability, the grease will cause some of the bearings to stick to the bottom of the pole. Hmmm….

Ok, onwards…

I coupled the 100rpm N20 motor to the gearbox and gave it a test. All went well and it was satisfying to watch the steel pole go up and down, twisting back and forth as it did so. It did take 6 mins or so for one complete cycle but that’s needed to get the required torque.

The next step was to try it out, building up to a weight equivalent to the final build and see how well everything coped. So I filled a 6 pint milk container with water and attached it to the pole as the first step.

I switched on power and, as it took the strain, the gearbox started to grind and stutter and then locked solid. Oh dear…

I removed and stripped down the gearbox and found the reason – a few teeth on some of the gears had broken off.

photo showing stripped teeth and damaged gears in the speed reduction gearbox
damaged speed reduction gearbox

So it turns out that the speed reduction gearbox I chose simply can’t cope with the required torque – it couldn’t even cope with around a quarter of the required torque 🤪

I’ve spent a good few hours online trying to find an alternative. I’ve fired off a few emails to suppliers of those that look likely, so we’ll see.

A reminder of the mechanism’s core requirements

The motor has to be driven by a single lithium ion battery, down to 3.7v

RequirementReasoning
The motor has to be driven by a single 18650 lithium ion battery, down to 3.7vThe readily available TP4056 charging module can, with a small mod, detect darkness and then switch the motor on until everything is reset to the sunrise position
Absolute minimum of 2 120W solar panelsIdeally this would be 4 solar panels, giving an additional weight of 7.2kg, but 2 would do.
Torque needed at a minimum is around 3.5Nm (torque calculator)
The total weight of pole, frame, top pole mount and 2 solar panels is approximately 15kg, and the lifting force is applied at a distance of 45mm from the gearbox shaft.

If I can’t get a gearbox capable of handling the required torque, I’ll need to rethink a lot of the above. Fingers crossed! 😜

Scaled-up Solar Tracker – proof of concept

see part 2

an annotated photo showing the proof-of-concept design for a scaled-up solar tracker
scaled-up solar tracker version with major parts labelled

The previous final solar tracker was good for 3 x 10W solar panels (and could probably have managed a couple more).

I want to scale it up so it can cater for 400W of solar panels or better. The main hurdles to overcome:

  1. With increased surface area, the ability to withstand high winds
  2. The increased weight of 400W worth of the solar panels
  3. A method of mounting the solar panels on the lift-and-twist pole
  4. Making it portable so it can be used both at home and taken on camping holidays
  5. Mounting the finished build – allowing for temporary or fixed location

I think I’ve solved the first two by:

  • building a box made from 9mm plywood, using reinforced metal brackets to join the sides, top and bottom together
  • using a pulley system with 3mm nylon cord to do the heavy lifting, with a central reinforcer dowling to reduce the strain on the top of the box where the pulleys attach
  • using a gearbox with a 1:810 reduction ratio to get much more torque than given by the 1:90 used in the earlier version.
watch it in action

Differences between the proof-of-concept and the actual design

While waiting for parts to be delivered, I’ve progressed with various substitutes from the actual design.

I’ve used a length of wooden dowel inside the aluminium guiding tube. The design calls for a stainless steel tube with the bottom end closed off.

The mechanism that the lifting eyelets are attached to inside the aluminium guiding tube is currently a short piece of dowel. It’ll be replaced by a 12mm high stainless steel bar, with a 2mm deep recess in the top to take some 3mm ball bearings. The closed end of the stainless steel tube will rest on the ball bearings.

I was sent the wrong gearbox – it had a reduction ratio of 1:55 instead of the 1:506 ordered. I’m fighting a battle with the suppliers to get them to replace it, so in the meantime I’ve taken the opportunity to order one from a different supplier with a 1:810 reduction ratio – as I think it’ll better be able to do the heavy lifting.

Still to resolve

I still haven’t worked out how to attach the solar panels to the top of the stainless steel lift-and-twist tube.

On the one hand, they need to be detachable for portability, and on the other, they need to be able to be fixed firmly to the tube to resist high winds.

I’m not convinced that the 2mm wall thickness of the stainless steel tube is going to be strong enough.

Once it arrives I’ll be able to test it and see if it’s ok.

Lessons learned from this proof of concept

I’m stupid, hehe!

It wasn’t until I built it that I realized the 2 times mechanical advantage gain of the block-and-tackle was entirely pointless because it meant I had to have twice the diameter on the rotating plate than I’d otherwise need.

And having twice the diameter doubles the torque needed!

For the unitiated, torque is a measure of the rotational force-at-a-distance-from-the-centre – if you increase the distance, you increase the torque needed.

Without the block-and-tackle, I only need a diameter of 4cm for the rotating plate. So I can get rid of it, simplifying things while getting the torque I need.

Read more about solar trackers

Wikipedia does a good job in covering the concepts and advantages of solar trackers.

Speed-Sharer for promoting from the Zazzle ShowMe Forum

Newly released tool from the Nifty stable – promoting from the Zazzle Show Me Forum is now easier and quicker than ever.

annotated screenshot highlighting the major features
tool’s handy extras highlighted

Affiliate Benefits

  • Saves you time – the Nifty approach is quicker and easier
  • Makes it easy to get at the products / collections shared in the Show Me forum
  • Restrict to store lets you get only shares from your favourite store
  • Share to Twitter and Facebook and pin on Pinterest at the click of a button
  • As more designers find out about the tool, the more they’ll put into the ShowMe forum for us – and they’ll be organised by topic – nice!
  • Your referral id and tracking code are used as normal – if you’ve got a Nifty Promoter Program subscription, you’ll get clean links
  • Pinterest doesn’t like it when different people share the same image. Get round this by using image frames – then chances of that happening become very remote.

Find the new tool in the Nifty Promo Control Panel in Step 2 under Share individual products with Speed-Sharers

Designer Benefits

  • Now it’s so easy for Nifty-ers to share from the Show Me forum, it’s another way to get in front of real affiliates
  • More of your great designs / collections will be promoted when you post to an appropriate topic (aka thread) there
  • Posting to very specific topics will help you help affiliates even more
  • You can use the Speed Sharer as well
    • advance to a 50/50 referral split when you put in your referral id
    • stay on top of things by seeing what products / collections you’ve already shared by using the ‘Restrict to store’ feature

So what are you waiting for? Here’s a link to the Speed-Sharer for promoting from the Zazzle ShowMe Forum

Features

  • Twitter, Facebook and Pinterest buttons for easy sharing / pinning there
  • To help you see where your successes come from, your chosen tracking code automatically has the date appended and is prefixed by whatever button you click:
    • twt_ for Twitter
    • fbk_ for Facebook
    • pntrst_ for Pinterest
  • Topic Lister
  • Promote from a specific topic (message id)
  • Lots of help for each feature
  • Filtering by the date a topic was created:
    • today
    • since yesterday
    • last seven days
    • this month
    • since last month
    • all time
  • ‘Restrict to store’ lets you see only products / collections from the given store
  • Handy link to Zazzle’s community search page
  • Link given to the topic for the displayed product / collection
  • Image frames for Pinterest to help keep your pins unique

We’d love to hear what you think, so drop off a comment and let us know! Thanks 😎

The NiMH solar rechargers saga continues….

The one thing holding me up on doing the tutorials for the rechargeable NiMH circuits is the global semiconductor shortage.

location for the LM317LZG to-92 package – no room for the larger T0-220 package

The AAA recharger version doesn’t have much room and so needs to use the TO-92 version of the LM317 voltage regulator. As you can see, there’s not enough room for the larger TO-220 package

Here’s what the TO-92 package looks like:

TO-92 package

I ordered a bunch from Farnell and was initially given a delivery date of Dec 17th (2021) but, as the day approached, it shifted to Dec 26th… then Jan 7th, then Jan 21st, then Jan 31st and it’s now at Feb 7th.

So I’ve ordered some from ebay and when they arrive (tomorrow?) I’ll cancel the order with Farnell.

I’m not happy about the delay but I have managed to make progress with other projects while I’ve been waiting.

The prototype solar tracker is now in its final version and I’ve been playing with some 1W warm white LEDs to use with the batteries it’ll charge. That way I can use them in place of some of my mains-powered lighting, helping a little to reduce my carbon footprint – and save money on electricity bills at the same time. Nice!

Watch for blog posts about them both.