.PS
gen_init
  linewid = linewid*0.8
  circlerad = 0.35/2
  bw = boxwid/2
  bh = boxht/2
# Gimbal.m4
# https://tex.stackexchange.com/questions/734796/how-to-create-a-gimbal-model-for-one-axis-using-tikz

#gen_init
  iflatex(command "{\sf
    \newcommand{\Sub}[1]{{\hbox{\scriptsize `#1'}}}")
Gimbal: [
textht = 15bp__
circlerad = 8bp__

 Ir: arrow right_ linewid*3/2
  { "Current" ljust at Ir.start+(-5bp__,textht) "reference" ljust
    "$i_\Sub{reference}$" ljust at Ir.start-(0,textht*2/3) }
 Ka: box "$K_a$"
  { "Current" at Ka.s -(0,textht) "amplifier gain" }
  arrow right_ linewid*3/2
  { "Motor" at last arrow+(0,textht) "current" }
 Kt: box "$K_t$"
  { "Motor torque" at Kt.s -(0,textht) "constant" }
  arrow
 S1: circle; {"$-$" at S1.n above ljust; "$+$" at S1.w above rjust }
  arrow right_ linewid*1.2
 GI: box "$\frac{1}{J_\Sub{s}}$"; arrow "$\omega_h$" above 
  { "Gimbal inertia" at GI.s -(0,textht) }
 S2: circle at Here+(0,3/2*boxht)
  {"$-$" at S2.e above ljust; "$+$" at S2.s below rjust }
  { arrow <- right_; "$\omega_b$" above rjust }
  arrow left_ from S2.w to (GI.e,S2)
 Bv: box "$B_v$"
  arrow left_ "$T_\Sub{viscous}\mathstrut$" below from Bv.w to (S1.e,Bv)
 S3: circle "$+$"
  { arrow <- from S3.w; "$T_\Sub{ext}$" above ljust }
  arrow from S3 to S1 chop
 Fc: box ht boxht*3/2 at Bv+(0,boxht*7/4)
  arrow from Fc.w to (S3,Fc) then to S3.n
  "$T_\Sub{friction}$" at (S3,Fc) above
  [ Orig: Here; thicktmp = linethick; thicklines_(0.4) 
   V: arrow from Orig up_ Fc.ht*5/12
   H: arrow right_ Fc.wid*5/6 with .c at Orig; thicklines_(thicktmp)
    line thick 1.2 up Fc.ht/2 with .c at Orig
    spline 0.55 thick 1.2 down_ boxht/5 right_ boxht/9 \
      then right_ boxwid/9 then right_ boxwid/4 up_ boxwid/8 
    { "$F_c$" above rjust }
    spline 0.55 thick 1.2 from last line.start up_ boxht/5 left_ boxht/9 \
      then left_ boxwid/9 then left_ boxwid/4 down_ boxwid/8 
    { "${-}F_c$" below ljust }
    ] with .Orig at Fc
 Gl: box wid boxwid*5/4 with .e at GI.e+(0,-boxht*2) \
  "$\frac{\omega_g^2}{s^2+2\zeta \omega_g s + \omega_g^2}$ "
  { "Gyro lowpass" at Gl.s -(0,textht) }
  arrow from Gl.e to (S2,Gl) then to S2.s
 Gd: box wid boxwid*5/3 at (Kt,Gl) \
  "$\frac{(d^2/12)\,s^2 - (d/2)\,s + 1}{(d^2/12)\,s^2 + (d/2)\,s + 1}$"
  { "Gyro delay" at Gd.s -(0,textht) }
  arrow left_ from Gl.w to Gd.e
  arrow left_ from Gd.w chop 0 chop
 S4: circle "$+$"
  {"Gyro noise" at (S4,last ""); arrow from last "".n to S4.s }
 Rm: arrow left_ from S4.w to (Ir.start,S4)
  { "Rate" ljust at Here+(0,textht) "measurement" ljust }
    "$w{}_\Sub{measured}$" ljust at Here-(0,textht*2/3)
  
]
# "Single-axis gimbal model" below ljust at Gimbal.sw+(0,-5pt__)
  iflatex(command "}%")
.PE