Propulsion Type Overview - Wiki


#1

This is a WIKI post summarizing all the various drive systems that have been discussed here so far. I am sure I missed a few. Please feel free to update this post directly (I’ll make it a special Wiki post) and please feel free to add links to other posts and external references as you see them fit.

1) Inrunner with Planetary Gearbox

Pros

  • High torque allows using large props (~120-150mm diameter)
  • Good efficiency with larger props
  • Manageable currents (between 15-50A)
  • Inrunners around 500kv can be used
  • Low drag with small(er) diameter inrunners
  • Easy to cool

Cons

  • Fragile planetary gearbox, not designed for fast constant input speeds
  • Gearbox can be expensive and hard to find
  • Additional weight, pod length and overall complexity
  • Gear noise

2) Inrunner Direct
Threads:


Pros

  • Simple
  • Quiet
  • Smooth to ride

Cons

  • High currents (can easily exceed 100A on start)
  • Generally less torque with similar diameters
  • Hard to make/find low kv inrunners motors with small diameters
  • Reduced efficiency with smaller props or jet drives to manager higher rpm

3) Outrunner + Planetary Gearbox

Pros

  • Planetary gear may last longer because of lower input speeds with low kv outrunners
  • High torque allows using large props (~120-150mm diameter)
  • Good efficiency with larger props
  • Manageable currents (between 15-50A)

Cons

  • Motor not easy to cool
  • Bigger Outrunner diameter, more drag
  • Planetary gearbox still a fragile component
  • Planetary gearbox can be expensive and hard to find
  • Additional weight, pod length and overall complexity
  • Gear noise

4) Outrunner Direct
Threads:


Pros

  • Availability of low kv Outrunners
  • Lower motor cost

Cons

  • Motor not easy to cool
  • Bigger Outrunner diameter, more drag
  • Generally higher currents, depending on prop size/pitch
  • Efficiency loss with small props / jet drive

5) Outrunner Direct Wet (epoxy sealed stator)

Threads:

Pros

  • Very simple
  • Good cooling
  • No shaft seals required
  • Availability of low kv Outrunners
  • Lower motor cost

Cons

  • Challenging stator and magnet sealing procedure
  • Motor bearing need to be replaced with ceramic or stainless steel ones
  • Bigger Outrunner diameter starting from 63mm, more drag
  • Generally higher currents, depending on prop size/pitch
  • Efficiency loss with small props / jet drive

6) Double Outrunner, single prop

Pros

  • Availability of low kv Outrunners
  • More torque than a single motor allows for a bigger prop

Cons

  • Cost – double motor, double ESC
  • Pod length
  • Cable/shaft routing may require special mast attachment design

7) Double Outrunner, 2 props front/back

Pros

  • Availability of low kv Outrunners
  • Twice the power ? Not sure

Cons

  • Cost – double motor, double ESC
  • Pod length
  • Will require special mast attachment design with mast in center

8) Double Outrunner, 2 contra rotating props in back

Pros

  • Availability of low kv Outrunners
  • Torque on pod cancels out
  • Supposable more efficient than normal props

Cons

  • Complicated design
  • Cost – double motor, double ESC
  • Pod length

9) Inrunner + Wet Belt
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Pros

  • High torque
  • Possibly more robust than planetary gears?
  • Cost

Cons

  • Needs a robust pod/housing – might require CNC work
  • Requires a belt system that works under water
  • High belt speeds could be a challenge
  • Additional drag from the offset pod

10) Inrunner + Dry Belt

Threads

Pros

  • High torque
  • Possibly more robust than planetary gears?
  • Cost

Cons

  • Additional drag from the offset pod and gear housing – likely more than with wet belt
  • Needs a robust pod/housing – might require CNC work
  • High belt speeds could be a challenge

11) Outrunner inside Board + Bevel/Miter Gear

Threads


Pros

  • “Unlimited” torque by using large diameter pancake outrunners

Cons

  • Motor noise and vibration
  • Long drive shaft down the mast – engineering challenge
  • Motor cooling

12) Rim Drive

Pros

  • Minimal noise emissions
  • Low space requirement - no shaft and no gearbox is needed
  • Sealing of moving parts is not necessary, rotor and stator can be sealed hermetically.
  • Since the blades are mounted to the rotor ring, there is no tip gap, reduces prominent source of noise
  • Everything just sounds awesome in theory – can someone please build one?

Cons

  • Reduced efficiency due to increased friction losses in the gap between rotor and stator

References

– WIKI POST END –