I wasn't sure if this was the correct forum to post this question but I thought I'd try. I'm new to RC drones/planes but I have a fair bit of experience with Arduino and electronics design in general. This year I'm on the organizing committee for my sons cub scout Pinewood Derby race and we are having a "Parents Race" where each parent can choose to build his or her own car. The key is that most of the rules don't apply for this race (since they aren't racing against the other scouts). You can do anything you want as long as it meets the weight restriction of less than 5.0 oz. So I wanted to build a car that has some sort of propeller which adds additional thrust to move the car faster down the track than the other cars.
So I started my design by choosing a bluetooth BLE board that I could control with my phone. This way I'd be able to turn on/off the propeller right before it starts and then stop it as it ends... all while being a few feet away from the car itself (note: you can't touch the cars once they've been registered). I settled on the Adafruit Bluefruit nRF52840 Feather board which seems to be quite small and yet should allow me to simply trigger the motor on/off via a phone. Next I wired up a quick circuit to drive these small DC motors. I chose these motors because they work with 3.3V which is all that the Bluefruit nRF52840 board can source from my 105mAh lipo battery and because they're fairly small and light. However, once I got my completed circuit put together and working, I've noticed that they don't really seem to add a whole lot of thrust (as far as I can tell). I don't really know how to measure something like that, but they certainly don't seem to do much when holding it with my fingers after I've turned it on.
I'm wondering if anyone has any suggestions as to what might be a better motor/propeller design that would still be light (somewhere around 3.0 oz) but provide a bit more thrust. I weighed all of my electronic components and together they only weigh about 1.5 oz so I definitely have a little more room to add something a bit bigger but I really don't know how to spec out something like this. Can anyone provide any guidance? I've added a picture so you can see my current design.
The transistor is a PN2222 Transistor. The power is a simple 105mAh lipo battery which is then powering the Bluefruit board. I believe there's an onboard regulator which outputs a clean 3.3V source. That's what is then going to the motor via the transistor.
In looking at a different store for motors, it looks like these are the same type of motor that I purchased. In the comments section it says that it can provide 38g of thrust which seems decent. But perhaps I need to get a bigger battery and a better propeller.
Run the motor power direct from the Lipo NOT via the Arduino regulator. And the 105mAh battery might not be good enough unless it has a reasonable C-rating. Those motors can easily take 1A or more depending on the propeller fitted.
And a PN2222 is not a good idea either. A small logic level MOSFET would be much more efficient.
If you build a DC motor and coin cell box into the car and put the ON switch in/on the front of the car so when the gate opens the motor runs. The weight you would put into a controller w/BT and a propellor can go to moar battery.
GoForSmoke:
If you build a DC motor and coin cell box into the car and put the ON switch in/on the front of the car so when the gate opens the motor runs. The weight you would put into a controller w/BT and a propellor can go to moar battery.
I agree, you are looking for all out POWER, so forget remote and put a switch on the front and let it go.
You can catch it at the other end and turn the power off.
KISS...
Tom.....
Thanks guys for the feedback. You're right that I should be feeding the DC motor directly from the battery and not from the 3.3V line from the bluetooth module. I'll switch that up and I think I'll also use a N-channel MOSFET rather than the transistor just to be on the safe side as I'm not entirely sure how much current this motor will draw with the propeller on. I think I am going to switch to these other 8.5×20mm Motor 16000KV Brushed Motors, three blade whoop propeller, and this 650mAh 1S Battery 3.8V HV LiPo Battery. There shouldn't be any reason why I couldn't power the bluetooth board and the DC motor using this battery, right? I mean, I don't really need to have the smaller 105mAh LiPo battery charging the bluetooth module and the larger battery simply powering the DC motor... In theory, it should be able to power both right?
Also, the reason why I don't think a switch option will work is because I can't be at the starting gate to turn it on before the race. No one is allowed to touch the cars once it's been registered... and the gate is really a just a small little metal stick that juts up from the bottom of the track... not a full gate per se. Anyway, I just figured the bluetooth module would be a little cleaner (assuming I can hide all this stuff inside the car).
TomGeorge:
I agree, you are looking for all out POWER, so forget remote and put a switch on the front and let it go.
You can catch it at the other end and turn the power off.
KISS...
Tom.....
