Friday, September 30, 2016

Electric Toothbrush Aircraft - Part 2 - The Propeller

Youtube video:

Continuing development of the Electric Toothbrush Aircraft using a high power rechargeable compact motor drive from a budget supermarket electric toothbrush.
Exploring the potential for educational value in getting that running a polystyrene glider kit flying "around the pole" on a tether line. Lessons can include feeling the torque effect then choosing the direction around the circle so the torque effect to maintain the line tension. Other lessons include a micro switch held on by line tension so cutoff happens if the line breaks.
Aiming here for a low cost kit - the motor unit, switches, propeller (and optional micro video camera) can be re-used for each group of learners. The aircraft and some accessories probably need to be new for each group project at a cost of about USD 10

Well performing fixed wing aircraft typically need to have a maximum thrust (weight force) of 25 percent of the weight. The measurements here are 35gram-force for an all up estimated weight of 100g - that includes carrying a micro video camera. So the maths says that this should be a good performer - 35 percent - too good to let loose on free flight - this will need a tether!

Low cost electric toothbrush is "Expert" sold by Countdown Supermarkets here in New Zealand. Cost is NZD 25 which is approx equivalent to USD 18

Propeller is "THO 387" from Acorn Models, Christchurch, New Zealand:

The next exciting episode will be the aircraft. So far after checking out a variety of kits, the best value I can find is this one:

Note that links are working as at 01 Oct 2016 but designs and supply can change quickly.

Monday, September 26, 2016

Electric Toothbrush Aircraft - Part 1 - The Motor

I lost my electric toothbrush so my wife bought me a low cost one from the local supermarket. This was remarkable for how powerful it was. Big noise and big brushing action. Then I found the previous more gentle one. And I thought - what to do with a spare high powered electric motor? Try powering a model aircraft with it! Maybe there is good STEM education value in here somewhere.

I cut around the case to remove the top and bottom. I needed to cut vertical slots in the middle section of the case to get it off. See photo below. After removing the interesting and possibly educational gearbox arrangement there is a compact motor drive unit with a rechargeble 2-cell NiMH battery. The cells are of miniature size so it delivers 2.4 V from half the usual NiMH battery weight.
I kept the bottom 5cm as a handy vertical stand. It also holds the unit nicely in the battery charger.

The toothbrush is "Express". Here in NZ it sells for NZD 20 in "Countdown" supermarkets. My checking suggests that this remarkably high power motor plus rechargeable battery plus charger for that price in one handy unit competes very well with the equivalent from gadget and hobby shops. Now .. can this thing fly?

Youtube Video:

Photos: I added the red insulation tape around the motor to tame its wild array of wires.