Question: Maple does not expand in Taylor

I created the next code:

f := M+2*e*sin(M)+(5/4)*e^2*sin(2*M)+(13/12)*e^3*sin(3*M)-(1/4)*e^3*sin(M)+e^4*((103/96)*sin(4*M)-(11/24)*sin(2*M))

fb := Mb+2*eb*sin(Mb)+(5/4)*eb^2*sin(2*Mb)+(13/12)*eb^3*sin(3*Mb)-(1/4)*eb^3*sin(Mb)+eb^4*((103/96)*sin(4*Mb)-(11/24)*sin(2*Mb))

x := cos(wb-w+fb-f)

rho1 := ab*(1-eb^2)/(1+eb*cos(fb))

rho2 := a*(1-e^2)/(1+e*cos(f))

P3 = (5/2)*x^3-(3/2)*x

R3 = GM3*(rho1/rho2)^3*P3/rho2

When I do 

R3exp := mtaylor(R3, [e, eb], 5);

it returns 

R3exp := R3

When I do 

> R3temp := series(R3, e = 0, 5);
> R3exp := series(R3temp, eb = 0, 5);
> convert(R3exp, polynom);

it returns

R3

Could you tell me how I can expand in Taylor R3 around e=0 and eb=0 ?

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