I bought an Aquazepp LT30 (short body, single speed, 12v with headlight) in the summer of 2017. Once a new battery was installed it was fully functional despite being well used and quite old. I was getting around one hours use out of the battery and measured my underwater speed at 33 m per minute, faster than swimming but not that fast for a scooter.
Though this was ‘slow’ around the same time Marcus Blatchford was scootering around Vobster Quay with a camera attached to the nose of his vehicle at similar speeds taking photos to be processed into a model (via the process of photogrammetry) so it was ideally suited to the task of accompanying him for which many a pleasant dive was had cruising through the wintry atmospheric waters of Vobster Quay.
I was already planning on upgrading my batteries to lithium based chemistry and had been searching Hobbyking for suitable packs, some 16 ah packs came up at a good price so I purchased six of theses giving me 96 ah Vs the standard 33 ah plus the benefit of a higher voltage as these were 4 s packs which give 16.8 v when full and 12 v when empty.
I was unsure if the standard 12v motor would be able to handle the extra power but installed the batteries anyway and took the scooter for a dive. A very enjoyable 90 minutes was spent whizzing back and forth to the end of Brixham Breakwater and back, and back and back…until the scooter seemed to loose power, I had assumed the packs were just flat so ended my dive very happy that my modification had improved both the speed and the duration of the scooter. Brixham breakwater is about 900 m in length and it had taken me just under 20 minutes to reach the end so a big improvement in speed over the lead acid batteries had been achieved.
The scooter was taken home and the batteries charged, and I took it for another dive at Vobster Quay expecting to cruise around faster than before, unfortunately once the scooter was in the water the propeller was making a feeble effort to turn much like it had at the end of my Brixham dive so a bit miffed I left it at the surface and went for a swim without it. Once I got home I took it apart and began to check the batteries had actually charged which they had, on opening the rear motor compartment a burnt smell was apparent and the insides were covered with a thin layer of black dust, clearly the motor had burnt out given the extra power that it was being asked to convert from electricity to rotation of the propeller.
A source of motors from the larger Aquazepp models which run on 24 v was provided by a friend and an order quickly placed. The motor was a direct replacement for the 12 v motor, it just needed the drive gear fixing to the shaft which was achieved using a small screw fixed through the motor shaft. The 24 v motor is heavier than the 12 v motor so I had to remove some of the lead ballast that was required when swapping from lead acid to lipo batteries.
Confident that a motor rated to work at 24 v could handle 4s lipo packs some more test dives were performed using a power meter to assess the average current draw. I found that I was now able to travel at around 44 m per minute with the motor drawing 16 amps so I now had a maximum range of nearly 16 km (6 hrs) ! Not bad for an old Aquazepp !
Next on the improvement list was a rear handle like most other scooters have, the scooter needs two hands to drive comfortably in its standard configuration. A delrin handle and bracket was made and fixed to the shroud, a small PVC trigger box was welded onto the main body which contains a magnet and spring which are actuated by a lever on the trigger. This dramatically improved the comfort when scootering, its now easy to control with one hand and only needs light steering input to instigate a turn.
The scooter is now capable of running at different speeds, a 50 amp Syren brushed DC motor controller has been installed which is controller by an Arduino UNO. The sketch loaded onto the Arduino reads the output from a hall effect sensor mounted to the inside of the hull. On the outside of the hull in the same location is a small plastic rod with magnets embedded which can slide back and forth to increase or decrease the speed. Whilst noise is always going to be loud when using an Aquazepp due to the metal gears the motor seems to run better now it is being supplied through the controller. The speed as its currently set can be run anywhere between around 65 m/ m and 40 m/ m, this can be adjusted further on the surface by editing the Arduino sketch if required. The controller outputs a PWM signal and even running at my current top speed I’m not at 100% duty cycle yet but 65 m/ m seems fast enough for now if dive kit is worn, if snorkelling it is even faster !
The downside to using a variable speed over fixed speeds is monitoring battery consumption, with fixed speeds battery usage can easily assessed post dive and then used as reference in the future, with variable speed unless it is run at fastest or slowest then its hard to gauge where you have been on the scale.
