Rotational system with 32 motors

[Michel12]

Hello,

I'm building a rotational system with 32 rotors/motors that I want to try out under water. And I would like to adjust the speed of all the motors ranging from 0 to 120 RPM and do this with a RC control system. So basically I want to hook all 32 motors up to one receiver but I need some help with the electronics.

I would like to keep every thing as small as possible, therefor I thought of using a MicroFlight Transmitter/Receiver and  Solarbotics Geared Pager Motors (25:1) and 3.7v Single Cell Li-polymer Battery(s) with a Max Discharge of 15C (1350mA) (see pix) It is possible to wire several motors on to one MicroFlight receiver in parallel, as long as the total current does not exceed 3 amps or the capability of the battery. (whichever is lower)

Note, my original plan was to use gears (see design pix) but the Solarbotics motors have a transmission belt output instead of a gear, and I think this is probably safer incase some rotors touch each other etc.  The question I now have is the generated rotational speed (RPM) when using 32 motors and that one receiver.

And here is were I would like to get some help or suggestions with figuring out the RPM's, I was thinking:
- input of 3V / 32 (motors) = 0,094V
- Unloaded RPM (3V): 920
- 920 * 0,094 = 86 RPM
- Belt transmission: 86/5 = 17 RPM

So if I go full throttle would my speed be 0 -> 17 RPM ?

If that's the case wouldn't it perhaps be easier to use regular brushed motors (11 Ohm) and a resistor to gear the speed down so I end up with a throttle speed of 0 -> 120 RPM ?

kind regards,

m.


http://www.microflight.com/Online-Catalog/Receivers


http://www.solarbotics.com/products/gm15/specs/

Designs:

[Razor Concepts]

Motors will not turn at 0.094 volts under load of a prop underwater. Don't wire them in series, parallel them so that the voltage (regulated to 3v?) is higher.

[knossos]

I would like to keep every thing as small as possible, therefor I thought of using a MicroFlight Transmitter/Receiver and  Solarbotics Geared Pager Motors (25:1) and 3.7v Single Cell Li-polymer Battery(s) with a Max Discharge of 15C (1350mA) (see pix) It is possible to wire several motors on to one MicroFlight receiver in parallel, as long as the total current does not exceed 3 amps or the capability of the battery. (whichever is lower)

...

And here is were I would like to get some help or suggestions with figuring out the RPM's, I was thinking:
- input of 3V / 32 (motors) = 0,094V
- Unloaded RPM (3V): 920
- 920 * 0,094 = 86 RPM
- Belt transmission: 86/5 = 17 RPM

So if I go full throttle would my speed be 0 -> 17 RPM ?

Since you are wiring your motors in parallel, the voltage to all motors would be the same.

- input of 3V / 32 (motors) = 0,094V 3V
- Unloaded RPM (3V): 920 RPM
- 920 * 0,094 = 86 RPM
- Belt transmission: 86/5 = 17 RPM 920/5 = 184 RPM

[Michel12]

Motors will not turn at 0.094 volts under load of a prop underwater. Don't wire them in series, parallel them so that the voltage (regulated to 3v?) is higher.

Hi Razor, thanks for your reply. My electronics knowledge is actually almost 2nd to none, sorry I've ordered my Robotics bible and I'm waiting for it but I thought I already asked someone.

So what you are saying is when I divide the 3V by 32 = 0.094 V  then I'm wiring them in series. If I wire them parallel they keep having 3V input and I'm not reducing the speed and keeping the Unloaded RPM of 920. With the transmission belt I could get a speed of about 920/5 = 184 which is probably quite okay if I handle the throttle carefully? What about the batteries can I put 5 or 10 of them parallel on the input and keep a 3V input or do I get a 3 * 5 = 15 V input or is this the case when I put them in series?

[Michel12]

- Belt transmission: 86/5 = 17 RPM 920/5 = 184 RPM

Thx Knossos, Has someone got experience with using a full throttle speed of 184 would I be able to just slowly speed up from 0 to 20 RPM or do these things go rapidly?

What about using a resistor (in series/parallel) to slow things down?

[Michel12]

Ok, I got my answer to what happens to the overall input voltage it stay's 3 V when in Parallel.


source: http://www.batteryuniversity.com/partone-24.htm

Parallel connection of four cells.
With parallel cells, the voltage stays the same but the current handling and runtime increases.

This leaves me with only 2 questions:
- If I use 32 motors and 8 batteries wouldn't the current be to big for the print to handle?
- If I add a resistor in parallel or series would that decrease RPM or will it prevent the motors from working properly?