Science Buddies: "Ask an Expert"

Posted on behalf of educator
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I wanted to try this project with my class, I can't get the car to move, it seems the battery pack is to heavy for the propeller- any suggestions?

we went with the battery pack with the switch option and the only other change was the propeller's link says no longer available, and I couldn't find any other 4 blade fans, used these 3 blade fans, for the 1mm shaft

part seemed to be a ill-fitted shaft/propeller sizing, I thickened up the shaft with some hot glue, I get a better faster spin on the blades, but still barely moving,

might we need bigger beads for the wheels ( diameter was not specified)

unfortunately, can't view videos with settings for the school computers.

thank you for any suggestions,
also any other ideas of how to repurpose these components for another project if we can't find a fix?



[Note: activity url https://www.sciencebuddies.org/stem-act ... peller-car
Information about the direction of the propellers is in the Digging Deeper section and more discussion here: viewtopic.php?p=77074 ]

Hi -

I don't think your issue is the battery packs, the plastic cover doesn't add that much weight - most of the weight is the batteries themselves.

I think the first thing to check would be what happens if you just push the cars and let go? If they stop immediately or don't roll very far, there is probably too much friction between the wheels and axles. The wheel diameter shouldn't be critical, but if there's too much friction for the fan to overcome, it's never going to move.

Also make sure the propellers are spinning the right way (if you hold the car in one hand and hold your other hand behind the car, you should feel air pushing your hand). If the air is blowing the wrong way, reverse the wires.

If that isn't the issue, unfortunately there are lots of those little propellers available on Amazon and we haven't tested all of them, so we can't say for sure which ones will work and which ones won't. Another idea if you still can't get it to work - try building a car with two motors. Connect both motor's positive wires to the battery pack's positive wire, and both motor's negative wires to the battery pack's negative wire (this is called wiring them "in parallel" - as opposed to wiring them "in series," where you would connect all the wires in one big loop end-to-end). Make sure the motors are both spinning in the same direction and have matching propellers (if not, you will need to reverse one of the motor's wires). That MIGHT get you enough thrust to push the car, but there's a limit to how much power the batteries can provide at once - so two motors doesn't necessarily mean twice as much force. I haven't tested it but it's worth a shot if nothing else works.

If none of that works, you could try putting off-center weights on the propellers to make "vibrobots," which are tinier versions of our larger Art Bot and Brush Bot projects:

https://www.sciencebuddies.org/science- ... /vibrobots

https://www.sciencebuddies.org/science- ... ld-art-bot

https://www.sciencebuddies.org/stem-activities/brushbot

I hope all of that helps, please let us know if you can get it to work.