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SOLVED

## Re: ODESolve with a limit

OK  !

Sorry I missed that.

According to my solution the current reaches 10 A at t=2.848 ms.

Luc

## Re: ODESolve with a limit

Whew!

Disagreeing with you is usually a losing bet!

Highlighted

## Re: ODESolve with a limit

I guess now your solve block models the current limitation correctly, assuming a(n ideal) current limiting device in series with the motor.

Luc

## Re: ODESolve with a limit

The current limiting 'device' is just academic at the moment.  I'm not much for electrons so won't even speculate on what it could be.  Also, at least for this problem, I'm told kt = 1/ks.  I believe this is derivable but haven't done it myself yet.  Also, I believe the simulink answer is actually per this picture - I'd previously been plucking the wrong current.

Sapphire III
(in response to DJF)

## Re: ODESolve with a limit

If kt = 1/ks the units don't balance.

## Re: ODESolve with a limit

Fred,

it's not the derivative of T (T'(t))  but T(t) itself that is equal to n*k.t*i(t)...

Luc

## Re: ODESolve with a limit

{to DJF}

Ah, and then your simulation starts at t=0.1 s, rather than at t=0...?

Luc

## Re: ODESolve with a limit

yes, although that is completely arbitrary - just done to show what happens before voltage is applied.  Starting at t=0s is fine.

## Re: ODESolve with a limit

That's the problem with typing in a problem from a picture.  Correct solution attached.

## Re: ODESolve with a limit

Now your curve matches the (corrected) curve of DJF. Two independent methods arriving at the same answer. That gives confidence.

Unfortunately (for me) Mathcad 11 doesn't like the construction with the min():

That is: it refuses to limit i(t) to 10   !

But strangely the w(t) curve resembles yours...

Luc

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