Managing Crumble class use

Working with class sets of Crumbles (or any similar device) in a primary class is a lot different from working with them on your own or in small groups.

It is impossible to keep your eye on all the groups and therefore wiring mistakes are going to happen.

And, of course, the occasional equipment failure is also going to lead to problems.

I’ve been trialling the use of Crumbles in several of my schools and come to the following conclusions as to to the main issues and ways of  minimising them.

1.  Power/Battery shorts.

This is the most serious as it can lead (in the worst case) to batteries catching fire and children getting minor burns.

The main cause of shorts is exposed croc clips touching each other when the covers have slipped off.

Therefore it is essential that before any lesson starts, that all croc-clips have their covers on – some will slip off during lessons but by ensuring that they are OK to start with, this will minimise the chances of short-circuiting the battery.

Some methods of stopping the covers from slipping off in the first first are currently being tried out but until a solution is found – please be careful 🙂


2. Power being incorrectly connected to Crumble/Crumbs

The Crumble itself is pretty robust and designed to withstand quite a bit of abuse when it comes to mis-wiring but some Crumbs and other external components might not be so robust.

I INSIST that Red and Black are ONLY used for power connections e.g from battery to Crumble and from Crumble onto Crumbs/Sparkles and I really recommend that you stick to this and not be tempted to let anyone use different colours for power or use the Red/Black for any other puposes (Red traffic light being the ONLY exception)

The earlier battery holders that were available, which are not marked with +ve and -ve, can also cause confusion.  I recommend marking which is which if at all possible – I use red insulation tape to mark the +ve.

Standardise on positioning the battery to the left of the Crumble with the wires connecting to the + and – at the top of the Crumble.

3.  Spare Set

No matter how many sets of Crumbles (and accessories) you have – ALWAYS keep one set back for spares/substitution testing. DO NOT be tempted to reduce group numbers and use it up!

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6 Responses

  1. David Kempton says:


    I think that the answer to the batter problem is to solder on a battery box connector. Please see link to photo below. I have used this successfully in a group of 10 pairs of students with no power problems. The power terminals are still accessible for croc clips if necessary.

  2. Ian says:

    Very interested in your work. I teach scratch in South west and expanding into pi and have just discovered crumble. Seems far better for primary. Would love to chat.
    Cheers ian

  3. Robin says:

    Thanks for your comments. I’ve been using Crumbles with yr 7s and hhad come to the same conclusions about the colour coding.

    I’ve wired the battery boxes using soldered in screw terminals to try to reduce the risk of shorts, and I’m also encouraging the students to put the noses of the croc clips through the connnection holes rather than laying them flat (croc biting a plank style) as otherwise they can slide sideways and short.

    We’ve killed two Sparkles and one motor driver so far…

    • cymplecy says:

      I’ll try out the vertical advice approach next time out 🙂

      I’m currently using a drop of this down the gap between wire and end of crocclip and that seem very sucesful inpreventing the cover slipping off – just need to see how long it lasts for

      Super Glue Gel

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