Don"t have a solution for designing a "mechanical" step, but do have a suggestion for "physical" steps.
Start by putting your right foot on the drawbar and push yourself up.
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Lift your left leg and put your left foot on the left platform/axle.
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Use your left hand to hold the governor control rod for balance.
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Push yourself up with your left leg, pull with your left hand, and swing your right leg over the seat frame.
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Do not use the speed control lever to pull yourself up because it could break.
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Put your right foot on the right platform/axle.
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Have a seat.
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These steps have helped me climb aboard "Sparky" our 51M and all three of our 51 MTs.