We carry freewheels and freewheel axle adapters so having a freewheel in the drivetrain is definitely an option. Our axle adapters are available for all common axle sizes such as 1", 3/4", 5/8", and 15mm.
These freewheels and axle adapters are available on this page: https://electricscooterparts.com/bicyclesprockets.html
We only list axle adapter for 1" axles on the page linked to above however if you need an adapter for a different size axle then please let us know and we will post a link to the shopping cart page that the adapter you need is sold on.
All of the parts could be purchased individually or we could make a kit out of them. The advantage of buying a kit is that it has a 10% discount over purchasing the parts individually, and that we install matching and labeled connectors on all of the parts so they are plug-and-play right out of the box.
The factory that we get our gear motors from does not make a 24 Volt 600 Watt gear motor and only produces a 36 Volt 600 Watt version. However we do carry a 24 Volt 450 Watt gear motor which is our item # MOT-24450G.
This 24 Volt 450 Watt gear motor is designed for electric bicycles so it does not have a flat mounting base like the 36 Volt 600 Watt gear motor does, so a mounting base would need to be fabricated for it. This 24 Volt 450 Watt gear motor of course has less power than the 600 Watt gear motor does but it also has other limitations over the 600 Watt gear motor such as having a smaller non- ventilated case which heats up quicker and hold heat longer than the 600 Watt motor's case does, and also having smaller less robust gears and a smaller diameter output shaft.
If you need to use a 24 Volt system and the 450 Watt motor is not powerful enough then two of these 450 Watt motors could be used to increase the power output to 900 Watts. These 450 Watt gear motors have fairly short shafts though so machining a belt cog to fit it might be a challenge.
Another option which will be available next week is a 48 Volt 1000 Watt gear motor. We will be receiving these motors and adding then to our site in the next week or two. They will be our most powerful gear motor and will open up a whole new level of power to our beach wagon kits.
Regarding brakes they may or may not be needed depending on the terrain that the beach cart will be driven on and parked on. With a gear ratio that provides a top speed of around 3 MPH there will be a significant amount of motor braking when the throttle is released. The more weight that the cart is loaded with and the steeper incline that it is traveling down will lower the amount of braking that the motor will provide. The motor braking tends to be strong but gradual. Motor braking will not completely stop the cart on downhill terrain so the final power to stop the cart when traveling downhill will need to be provided by hand or with a mechanical brake.
If you want to be able to stop the cart quickly and completely for safety reasons when traveling downhill without stopping and holding it by hand then adding a mechanical brake would be necessary.
You could build the cart and take it out for a test run to see if the motor braking is sufficient, and if it is not then add a mechanical brake to the cart later.
Here are photos of the different switch options.
A freewheel only disengages the wheel from the sprocket in one direction and does not act like a neutral gear in a transmission. Freewheels are always in the same state and can not be switched on or off.
The freewheel allow the driven wheel(s) to roll freely without drag from the chain and motor in the direction that the motor powers the wheels in. This allows the beach cart to be pushed forward by hand without any resistance from the motor. Without a freewheel the cart would be difficult to push by hand when the motor was off. The freewheel allows the beach cart to coast when traveling downhill. If there is no freewheel in the drivetrain then the motor acts as a brake when going downhill.