Updating extra fields pivot table laravel - laravel

Question

I have 3 tables,
a pedido(order) table, a product table and a pedido_product table
I have an extra field cantidad in the pedido_product table that i´m trying to update for each product orderd
I'm able to update the extra fields with hardcode values in my update method, my cantidad get's updated correctly
$productId = 2;
$cantidad = 1.1;
Pedido::find($pedidoId)->products()->updateExistingPivot($productId, [
"cantidad" => $cantidad
]);
Now i have a form where i try to update the cantidad on each product on the same request
{!! Form::open(array('action' =>
['PedidosController#update', $pedido->id],'method' => 'PATCH')) !!}
#foreach ($pedido->products as $product)
{!! Form::text($product->pivot->product_id,
$product->pivot->cantidad, ['class' => 'form-control' ,'id' => 'cantidad']) !!}
i get what i want, an array with a key refrenced from the product_id and the value of the to be updated cantidad. but now how do i bind productId and cantidad in the update method to the array i recieve from my form and loop through them in my update method?
$pedido = $request->input();
$productId = ? ;
$cantidad = ? ;
Pedido::find($pedidoId)->products()->updateExistingPivot($productId, [
"cantidad" => $cantidad
Thanks
edit
I didnn't found the ansert but i changed the approach, instead of updating them all at the same time, i update them one by one by opening the form after the loop and passing throug a hidden form that provides the product_id this does the trick
#foreach ($pedido->products as $product)
{!! Form::open(array('action' => ['PedidosController#update', $pedido->id],'method' => 'PATCH')) !!}
{!! Form::text('cantidad', $product->pivot->cantidad, ['class' => 'form-control']) !!}
{!! Form::hidden('id', $product->pivot->product_id, ['class' => 'form-control']) !!}