An old blunderbuss isolated over a white background

Lockdown Challenge: Online campaigns and potato wars

Image credit: Dario Lo Presti/Dreamstime

This week’s challenges for engineering families are to battle it out with air-powered artillery and to launch an online campaign.

As these weeks in lockdown continue, even though some people seem to think we are back to normal, it might be that tempers are becoming frayed particularly in the family home where most human contact over the past three months has been with people of the same surname. Maybe the answer is to let off a bit of steam with some DIY weaponry. Neil Downie’s project for the family this week is to make an air-powered gun that fires potatoes (or other root vegetables). In our second challenge this week, Crispin Andrews looks at how you can guide your offspring to create a useful online campaign.

The IET also has a host of resources, which adults can use to engage children with the world of STEM.

Lockdown Challenge #21 – Go into battle with Blunderspuds

In days of yore, a year or two before mobile phones and the Internet, there was a kind of huge musket, a heavy calibre rifle/cannon which fired a whole bunch of slugs. The aim of this kind of musket was so haphazard – bullets could fly almost anywhere – that it got christened the ‘Blunderbuss’. Because it fires potato bullets, and because its aim isn’t the greatest, I christened this gadget the ‘Blunderspud’.

Find some kind of metal or plastic pipe or tube for your barrel, 10-20mm in diameter and 5-600mm long. You also need a length of round wood or bamboo a little longer that fits loosely inside it to make your ramrod. Another similar length or just a simple stick that goes through the pipe is useful, too, to get the slugs out. If the pipe is thick-walled – as plastic pipe generally is - you need to bevel the edges of tubing – on the inside, so that the barrel will easily stick into the potato ammunition. Similarly, with a metal tube, try rolling an iron rod, drill end, screwdriver or something around inside at an angle it to cause the end to go a little wider than the bore. You need to do this to the end of the barrel so that the slug of potato it cuts is just a tiny bit bigger than the bore of the barrel and will grip and seal the air inside well.

Now add the handgrip and shield onto the ramrod. They are made by taping tightly over a wrap of tough plastic foam or bubble wrap. The idea of the shield is that it stops the slightly sharp end of the pipe accidentally cutting your hand: keep your hand around the grip (black on the photo), so that the shield (red in the photo) does its stuff. The other thing to make sure of is that the ramrod is just long enough to push the potato slug just up to the end of the pipe, but not to push it right out.

Blunderspuds equipment

The tools you need for your Blunderspud

Image credit: Neil Downie

You can make the ramrod longer, but then every time you fire, you will need to put two slugs, one at each end of the barrel, rather than just one. (Such a long ramrod has the advantage that two new slugs will give a slightly higher air pressure and fire the bullet further.) Your Blunderspud is ready – time for a test firing.

When loading, try rotating the barrel to and fro a little: that fixes it in position so that it doesn’t slip, and careful how you push it through the potato. You want a bullet the full width of the spud. Now do the same at the other end. Why put a bullet at both ends? Because in the Blunderspud, one spud slug is a bullet and the other is a piston.

What happens when you push the ramrod against the piston slug is that it slides towards the bullet slug compressing the air. The volume of air goes down and, using Robert Boyle’s Law, we know that the pressure has to go up (there’s a great little animation of Boyle’s Law on Wikipedia). When the air pressure has gone up enough, the bullet slug can’t grip onto the barrel any longer and shoots out.

Now take aim and push as hard and fast as you can. With a bit of luck, your spud bullet will fly out with a loud 'POP!' and go somewhere near the target. Didn’t get near the bullseye? No problem! You can now you reload the other end of the pipe and use your new piece of spud as the piston, and your old one as the new bullet.


  • How far can you get a spud bullet to go? 8m? 10m? 15m? More? What is the best angle to get the furthest shot?
  • How far away can you be and still hit a 300mm target circle?
  • Can you load and fire every ten seconds and still hit the 300mm circle?
  • Can you get your Blunderspud working on carrots? Carrot bullets will go faster. Blunderspuds fire potatoes at 15ms-1 or so, which is 30 miles per hour. I have calculated that carrots could go up to 50ms-1 (that’s a 100 miles per hour!) in perfect conditions, but you need to push a whole lot harder. BTW, its best to use large carrots and push the barrel into them sideways. Pushing small carrots down the barrel doesn’t work as well.
Here’s a video on the famous Carrot Cannon:

If you liked this, you will find lots more fun science stuff in my books like The Ultimate Book of Saturday Science from Princeton University, and for lots of other things (and a free copy of the Exploding Disk Cannons book),

Lockdown Challenge #22 – Launch an online campaign

You can do almost anything online these days. Why not encourage kids to run a useful online campaign? Run for class president when school returns; sell old toys; show support for local key workers, or protest against a perceived global injustice.

Get your child to work out what they want to do and then follow these steps to reach as many people as they can:

  • Work out precisely what you want to achieve and how to deliver it. Online, people have short attention spans, so get your point over concisely. Remember: Get Brexit Done. Black Lives Matter. Support the NHS. Clear slogans, clear messages without ambiguity. Buy My stuff. Stop smoking now. You could ask a question: Should sport be played during lockdown?
  • Know who your target audience is and where they hang out, online. Is your target audience local for a local issue, school mates, people of a certain age, persuasion or a specific interest group? What sort of social media sites do they use? What sort of content do they most engage with – photos, memes, cartoons, videos, more in-depth articles?
  • Have one online place where people can find out about your campaign? This could be a Facebook page, or if you prefer an alternative try MeWe, a Twitter account, or if you’re feeling ambitious you could set up a simple blog or website. If you’re just promoting a petition, signpost people to the petition site. Whatever your online base, Make sure it’s easy for visitors to find their way around your online place and that what you want them to do is clear – whether that’s join your campaign, support what you are doing, buy your stuff, share your message.
  • Piggyback on the news. There’s a lot going on at the moment that people feel strongly about. And a lot more happening around the world that people don’t know so much about. If your campaign is relevant, thought-provoking, or touches people’s emotions then it’s more likely to be noticed and actioned by more people.
  • Run an online event to promote your campaign. This could include live videos, Q and As and discussion forums, chat rooms where people can talk about your campaign and ask you questions, online poll to test interest in and reaction to, your content. You can share other details, interviews from well-known sources relevant to your event, link to other sites that share your campaign objectives. Choose the right platform, preferably one that works with your chosen online base. So for instance: Zoom, GoTo, Google Hangouts, Webex, Facebook event. Make sure you test all the technology you want to use before the day. Have a way of capturing the interest that you’ve generated during the event by encouraging them to sign up to your main campaign, or ‘like’ your page, website or blog.

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