The error message here is telling you that fs_1[1] is an element of an Array of Float64 but the value you are trying to store in it, is of type Uniform{Float64}.
instead of f_s = zeros.... do
f_s = Vector{Uniform{Float64}}(undef, length(t)+1)
or if you really need them to be initialized to zero
[Uniform{Float64}(0.0,0.0) for _ in 1:length(t)+1]