Monday, January 16, 2012

Thermal camera - the video!

Yes, I did make a video yesterday. It was perfect, cold enough to show every detail.

The results are astounding.

These tests also show why the tapered bands typically break about 7 mm in front of the pouch - because that is the hottest part! Obviously the leather pouch cools the band down a bit. The rubber breaks at the hottest point, which stores the most of the energy.

The tests with Destin's high speed cam and this thermal cam help me understanding rubber. Of course it was a known fact that the bands shoot better in warmer conditions, that the bands loose power when you keep them drawn out, that tapered bands tear at the pouch, and that the bands are getting warmer when you draw them out. But now there are explanations. I hope these tests will ultimately help us to make slingshots even better.


  1. Deer Jorg, My parents used to buy me cheap slingshots as a little kid and they broke every week and I only got them once a year. I always though of them as toys because of that, and now I find THE SLING SHOT CHANNEL! You have changed my perspective of slingshots so much, and I've learned a lot. I do have a question. Can you make a video on how to put on therabands? That would be nice.

    sincerely Niall.

  2. Niall, check out - you will find the download link for my band manual there, and also my band calculator.

  3. You state all we have known in the past, but I don't know that I can agree the greatest heat produced at the greatest strain is the primary reason for the consistent tearing. I would think it is primarily the greatest strain at the thinnest part that tears them there. Add the factor that that section is already over-strained and has lost some elasticity already and it tends to dictate the tearing. The very end (the absolute thinnest part) is normally doubled back on itself and thus has more mass to handle the strain than the area preceding it. I am not yet convinced that the heat generated is the primary enemy of the rubber as it's not that great of an overall difference. Heat has always been, it seems to me, to be more of a boost to the rubber than detrimental and has allowed easier stretch.

    Expert on rubber I am not, but that is the way it seems to me. I could be very wrong, so I will keep my mind and opinion open.

    Thank you for the thermal images which opened doors to our knowledge, but, as usual, brings out even more questions.

  4. Lord Robere, the hottest part is also the part that provides most of the energy. Therefore it is mechanically the most active part. This may be the reason for the tearing.

  5. That was a fascinating video! It would be cool to take pictures of the cannon with that cannon! :D

  6. Jorg! I am learning about this very effect in my statistical mechanics class at university!

    I wonder if you could make a draw more powerful by heating the band after it has been stretched? Then you could potentially exceed your own draw strength limitations.

  7. and what would happen, when you heat the rubber with something?