Scooter Design - What's different with the Cuda?

Hi,

Have lurked on this forum for many years (and learnt lots!) but this is my first post
We are currenltly looking for 2 new scooters. Having used Gavins and SS we thought our decision would be between those.

Have had a look more closely at the X scooter since reading the benchmark testing.

In partcular interested in the CUDA - but interested to know WHY it out performs the others.

I understand that part of it is the use of a brushless motor (right?) and it seems to be run at a higher voltage but how does the actual output of the motors differ between the brands?

Particularly:

• what speed do the props spin at
• what are the torque figures for the motors
• How else can they be compared?

Its a big decision for us to buy 2 scooters so we are keen to get it right and know as much as we can about what we are buying.

Thanks for any help you can provide

John

John,

Besides the motor (87% efficient at high speed), the battery technology that they use is a huge factor.....NIMh and Lion. Having no gearbox also improves efficiency.

The CUDA family of scooters represents the sum of all our experiences making and diving the Sierra scooters. We took everything that we learnt, wished for, dreamt about, and put it into the CUDA. We designed a motor to not only give higher speeds but also be extremely efficient (over 87%) at cruise speeds. This gives you the power to overcome the worst currents combined with the endurance for the longest explorations.

Click to expand...

On there website they have a page comparing the different scooters:

http://www.dive-xtras.com/pages/scooters/compare/comparison.asp

jborg:

Hi,

Have lurked on this forum for many years (and learnt lots!) but this is my first post
We are currenltly looking for 2 new scooters. Having used Gavins and SS we thought our decision would be between those.

Have had a look more closely at the X scooter since reading the benchmark testing.

In partcular interested in the CUDA - but interested to know WHY it out performs the others.

I understand that part of it is the use of a brushless motor (right?) and it seems to be run at a higher voltage but how does the actual output of the motors differ between the brands?

Particularly:

• what speed do the props spin at
• what are the torque figures for the motors
• How else can they be compared?

Its a big decision for us to buy 2 scooters so we are keen to get it right and know as much as we can about what we are buying.

Thanks for any help you can provide

John

Click to expand...

John,

I doubt the specs you seek will be of much help. What matters is peak power.

Many scooters use the same basic "back end" from the Oceanic Mako. This features a high torque, low rpm brushtype motor, adjustable pitch prop, and "kort nozzel"

These brushtype motors are simple, reasonably reliable and.... limited in output.

At around 500-600 watts these brushtype motors simply cannot dissipate heat fast enough to avoid damage. The limiting factor for designs using these motors is the maximum power output, and the power output / lbs of motor weight.

I'll point out that in the era when these DPV's were designed this power limit was not a concern because lightweight, high capacity batteries did not exist. The batteries limited the design, not the motor.

Brushless motors can offer some efficiency advantages over brush type motors but the greatest advantage for the DPV application is the ability to get much higher power outputs in a small lightweight package.

A key reason for this is the much improved heat rejection of a brushless motor. A typical dc brush type DPV motor has a wire wound armature that rotates inside a housing that contains permanent magnets. These wire windings deep inside the motor get hot and it's hard to conduct this heat away.

Brushless motors can be thought of as a DC motor that has been turned inside out, the magnets rotate, and the windings are on the outside. This allows for much easier cooling, and allows for much higher power output per volume, and per unit weight.

The 'Cuda' motor weighs about what the motor in a Gavin etc. weighs, but is capable of much higher, 1000 + watts, output.

The higher voltage is part of what provides the higher power output per unit weight or unit volume. If you for example imposed ~44 volts on a "24" volt Gavin motor you would certainly get higher power outputs, but the motor would quickly burn up.

Lightweight, high output motors are what allow the operating envelope of the Cuda to be so large.

Hope this helps,

Tobin

Thanks to the both of you - information has been very useful.

So, if the CUDA uses the same prop as the other x scooters the higher speed must be achieved through higher RPM, not pitch (although I understand this is adjustable as well).

I think a Gavin, SS etc rotate at a fixed speed of 1000rpm. The CUDA must roate at a similar rate to this for the same speed but it also must roatate considerablly higher as well when it reaches higher speeds

Think I am starting to get a grasp on it... ...

jborg:

I think a Gavin, SS etc rotate at a fixed speed of 1000rpm.

Click to expand...

No, not really. Much slower, and RPM is still a function of imposed voltage and load. The operator cannot vary the motor speed on these scooters, but that does not mean it is "fixed"

jborg:

The CUDA must roate at a similar rate to this for the same speed but it also must roatate considerablly higher as well when it reaches higher speeds

Click to expand...

At high speed the Cuda prop will be turning faster than the Oceanic based DPV's, but the difference is less than you might think.

Tobin

jborg:

Thanks to the both of you - information has been very useful.

So, if the CUDA uses the same prop as the other x scooters the higher speed must be achieved through higher RPM, not pitch (although I understand this is adjustable as well).

I think a Gavin, SS etc rotate at a fixed speed of 1000rpm. The CUDA must roate at a similar rate to this for the same speed but it also must roatate considerablly higher as well when it reaches higher speeds

Think I am starting to get a grasp on it... ...

Click to expand...

The 1000 rpm is the free speed, running with no load. as Tobin refers to, the speed under load in the water is considerably slower.

You are totaly correct in you second paragraph. The scooters only moving interface with the water is the prop, and as the props (SS,Gavin,X) are basicaly the same, the only real variable to play with is RPM.

really appreciate all the replys, am starting to get some things worked out in my head.