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Description about my project to drive an electric Stand Up Paddle (SUP)

Beeeeer

Abstract

Hi guys πŸ‘‹

this is the repo to document my SUP project. It is on the hand for me to not forget my ideas and schematics and on the other hand I hope that I can help someone by starting with her or his projects.

Regards!

Patrick

Disclaimer

I only show my personal experience / project by building up an electric SUP

  • I am not responsible of any damage you are producing by copying this project
  • Explicitly not for any fire, which can be caused by the battery

--> Please check the regulations for your country before you are starting with your project πŸ‘

As example in Austria 4,4kw systems (and shorter than 10m) do not need a license and you do not need a driver license (https://bootsfuehrerschein.at/)

Overview

So enough obligatory stuff...

I will show you the following point from my project and hints I have learned

  • A couple of links I found to get a feeling about the speed or your SUP and the needed energy
  • All CAD models will be stored here in the CAD folder (as Step and STL files) --> The modeling is done in Fusion 360 Personal so when you want access to the complete model feel free to contact me here
  • All electric wiring and components I have used
  • The Software I have used / written will be linked or stored in Software
  • A cost overview about the setups
  • Links to all parts

Hints

Basic fluid dynamics

First of all you cannot "calculate" the speed hard from any equation! You need to make guesses about different forces.

In industry application there are using CFD-Simulation to define the force on a numeric model. But I guess this will be a bit of overengineering for a SUP πŸ˜‚

In easy word you need this equation: Fdrag = cd * A * p/2 * v^2

Fdrag (in N) is the force we produce in the fluid

cd * A (A in m^2) is the geometry part of your SUP. cd is normally known from cars as Drag-Coeffient and defines how good your geometry is laying in the fluid. And A is the area which is projected in the length of your sup.

p (in kg/m^3) is the density of your fluid, for water it is 1

v (in m/s) is your velocity.

So in summary

  1. The drag force increases quadradic with your velocity!
  2. Reducing the front area decreases the drag force --> Higher load means that the front area in the water will be increased and so also the drag force
  3. Using a good shape is decreasing the drag force (That is the reason why boats are not formed like a block)

The drag in the water is not the only one. You also need to have a look on the drag your body is producing by standing on the SUP. But the density of water is a lot higher than the density of water focus first on your water components.

Links: https://en.wikipedia.org/wiki/Drag_coefficient

Calculating the target speed

So from the chapter before we learned that we cannot calculate the speed of our system by starting the project.

But we can do "number founded guessing" πŸ˜…

Therefore one option is to go over your propeller geometry and the rotation speed of your motor.

So in easy words: When your motor spins 1000 rpm (r/min --> rotation per minute) with your battery and your propeller "brings you" 10cm (cm/r --> centimeter per rotation) forward every rotation you will get the following speed:

1000 r/min * 1 cm/r = 100 m/min = 1,7 m/s = 6,1 km/h

Ok but 3 questions

  1. What means "brings you forward"?
  2. What is about the fluid dynamic from the chapter above?
  3. What is about efficiency?

Ok...

  1. The propeller has a pitch. So as example your propeller has pitch of 20mm it brings you 20mm forward every rotation. So here we do not go deep in the geometry of our propeller just take the pitch.
  2. Because we have no idea about the fluid dynamic values we need to guess a factor for our calculation. On experience a geometry factor of 0,75 is senseful.
  3. The efficiency of your motor is also really relevant when we talk about the rpm. Normally you get a KV value for your motor which means how many rpm per volt you generate. But normally your motor has a efficiency about 80% so this needs to be calculated in the rpm.

But!

There is a calculator online so you can forget all my words from before 😁

Link: https://www.offshoreelectrics.com/conversion.php

As described with 80% motor efficiency on my motors and 25% "slip" on the propeller my calculation is fitting the reality.

Ofcourse at the moment for slow speed (till 7km/h) --> As higher your speed will be as higher will be the fault, because your slippery will increase in quadradic way.

Project V1

Overview

About

Project V1 started with a set of electronic I had at home. Therefore the focus stayed on a very easy and cheap solution. With V1 I reached 3 km/h with a 3S battery and in V1.1 5 km/h with a 6S battery.

BOM (Bill of material)

This is explicit for the first draft of V1!

Before you start buying check also the subversion. So you do not need to buy this controllers when you want to build a 6S system!

Function Title Price Bought date Comment
Battery Amazon Link 42€ 28. April 2020 -
Motors (2x) Aliexpress Link 26€ each 15. August 2022 -
Controller (2x) Aliexpress Link 11€ each 12. May 2020 40A Variant
Battery Watcher Amazon Link 13€ (5 pieces) 30. April 2020 -
Arduino Supply Aliexpress Link - - Bought in a set --> Link just an example
Remote Amazon Link 25€ 28. April 2020 For a longboard
Arduino Nano - 3€ - I have no idea where all my arduinos from πŸ˜…
Cables / Connectors - 15€ - Depends on your favorit cables. I did everything with XT60
Wings - 1€ - Self printed
Waterproof Box Amazon Link 12€ 28. August 2022 -
Waterproof Cable holder Amazon Link 7€ (25 pieces) 27. August 2022 -

So in sum: 192€ on my side (72€ for this project the rest stayed already in my apartment)

Hardware / Mechanical parts

Mechanical_001

You see the mechanical design in the overview picture in attached version. The Step files are in the CAD folder. --> CAD/V1

The wing is based on a NACA (0018) profile without any camber. --> So "no camber" means it does not produce force in any direction

Mechanical_002

The wings are screwed with 3x M4 screws against the driving direction in the flap.

The motors are screwed with 4x M4 screws each.

Electric

Electric_001

Every side of a block in the overview represents a connector. On my side every big-line or powerline is connected with a XT60 connector. The both power cables from the controllers are soldered together in one XT60 connector to the power module.

The connector for the motor are 4mm motor connectors. (Amazon Link)

On the power module are 3 cables soldered to the arduino.

The interface to the receiver and to the logic input of the controllers is done with breadboard cables.

The battery watcher is plugged directly in the balancer connector of the battery. It is just to know the cell voltage while driving and get an acoustic warning, when one cell is under the defined end voltage.

Software

You will find the software in the software folder. --> It is not pretty but it does the job πŸ˜…

The software has only 3 features

  1. Distribute the input signal to both controllers
  2. Build a cruise control to not hold the receiver on throttle
  3. Watch the battery complete voltage and stop the controllers if the voltage is to low

Project V1.1

Because the motors are rated till 6S Battery config it is near to update the system for a higher RPM on the motors!

--> With this config I reached 5 km/h with my SUP. Of course, when the voltage decreases also the speed decreases: Speed

In general I am able to drive 45 min and 2,8 km with one 4500 mAh battery

Therefore I bought the following equipment:

Function Title Price Bought date Comment
Battery Amazon Link 102€ (2 Packs) 21. October 2022 -
Controller Amazon Link 43€ (4 pieces) 21. October 2022 -
XT60 Connector Amazon Link 6€ (5 pairs) 21. October 2022 -

So in sum 151€ extra costs


The mechanical and electric parts stayed the same.

Controller

The interface from the controller differ from the original one. Therefore the software changed from PWM to DShot. You will find the software in the corresponding subfolder.

The controller itself is a bit underpowered for my motor so I changed the configuration via the BLHeli interface.

I will show you a konfig setting I needed to change to power up my motor by I also burned one of the 4 controller with the setting and a other motor (a high RPM drone motor to test). So be really careful!

The config I changed: Config

To change it I connected the controller via an Arduino Uno.

  1. Connect the input pin from your controller with pin 0 from the Arduino
  2. Use the BLHeliSuite 16.7.x
  3. Flash the arduino to "Arduino BLHeli Bootloader"
  4. Connect to the controller with the interface "SILABS BLHeli Bootloader (USB/COM)"

Project V2

So the forecast will be true 😁

Battery

I will build up an own battery and use the LG INR21700 M50T Cells: Datasheet Link

In the configuration of 12S6P are 72 Cells so 1,3 kWh Capacity in theory. The cells can give continuously 3C so 15A in the configuration with 6P the Battery is usable till 90A. With 43V (12S * 3,6V) the Battery can be used till 3.9kW continuously.

Function Link Price Bought date Comment
Cells Nkon Link 300€ (75 Cells) 13. January 2023 -
2x Spacer Nkon Link 33€ (74 pieces) 13. January 2023 -
Battery Soldering Strip Nkon Link 22€ (8m) 13. January 2023 -
BMS Ebay Link 95€ 13. January 2023 -
Charger AliExpress Link 50€ 14. January 2023 400W without balancing
Connectors AliExpress Link 27€ (5 pieces) 14. January 2023 Waterproof 4 Pin Γ‘ 25A
Cable AliExpress Link 24€ (2m Red, 2m Black) 14. January 2023 7 AWG
Box Amazon Link 50€ 10. March 2023 Size L

So in Sum 601€

Powertrain

Function Link Price Bought date Comment
Motor + Propeller Flipsky Link 171$ 30. October 2022 -
Controller Flipsky Link 90$ 30. October 2022 VESC 50A
Bluetooth-Adapter Flipsky Link 26$ 30. October 2022 This is optional but makes the config easier
Cooler Amazon Link 10€ 23. February 2023 -
Crimps Amazon Link 10€ 23. February 2023 -

So in Sum with shipping 364$ or 381€

Mechanic

Function Link Price Bought date Comment
Fin Amazon Link 10€ 11. February 2023 -
Alu Holder - 25€ 13. February 2023 Lasered at a local manufacturer

You will find all CAD-Files in the CAD/V2 folder.

The idea was to build up a strong core from 5mm aluminium. This core will than be added by a wing of 3D-Printed PLA. So in the first picture you see the aluminium core (here was the propeller faced in the driving direction, this is changed now)

Init_Mechanic

Here is a picture with the PLA printed wing outlet on one site, how they look together and ready to drive:

Wing

Electric

Electric_002

Forecast

Because 5 km/h is still to slow I will exaggerate a bit 😁

The following motor is in delivery: https://flipsky.net/products/flipsky-inrunner-brushless-dc-65111-motor-160kv-3000w-for-surfing-boat-underwater-thruster-for-hydro-efoil?variant=37571726344379

It will spin 8k rpm with a 12S battery (so 2x 6S in series) and generates up to 3 kW πŸŽ‰

With the guessing from before I expect a velocity around 40 km/h but I will update this sheet when I set up everything.