[ODE] Fw: Problems in QuickStep

Russell Bartley russellbartley at kromestudios.com
Tue Jun 26 23:35:14 MST 2007


It was a bad value that I was setting with dJointSetUniversalParam()

I am now asserting it before putting it into the joint.

The bad value was beacuse of a non normalised matrix that I was using trig 
functions on. asin(1.00000001) = QNAN, not PI/2


----- Original Message ----- 
From: "Russell Bartley" <russellbartley at kromestudios.com>
To: <ode at ode.org>
Sent: Wednesday, June 27, 2007 3:52 PM
Subject: [ODE] Fw: Problems in QuickStep


>I just spotted a problem in my reasoning, sorry about this,
>
> the joint array is not an array of joints, but an array of joint pointers,
> so the memcopy is fine.
>
> I just need to find out why I have a bad limot.histop value.
>
>
> ----- Original Message ----- 
> From: "Russell Bartley" <russellbartley at kromestudios.com>
> To: <ode at ode.org>
> Sent: Wednesday, June 27, 2007 3:39 PM
> Subject: Re: [ODE] Problems in QuickStep
>
>
>> Sorry to continue this, but Im d like to get it straight in my head.
>>
>> To clarify which version I am using, it is a heavily modified version of
>> ODE 0.6, but the code in question hasn't changed since ODE 0.6 to the
>> latest snapshot that I got off the ode site.
>>
>> I tried to get the CVS version but it came up with an error.
>>
>> anyway.
>>
>> I found a situation inside of  universalGetInfo1() where at the end of 
>> the
>> function:
>>
>> constraint1 == false,
>> j->limot1.fmax == 0,
>> j->limot1.limit == 2,
>> and
>> limiting1 == false
>>
>> which meant that
>>
>> universalGetInfo1() was not incrementing m for the first constraint, 
>> while
>> adlimot() would later on.
>>
>> The m would not get incremented here becausse constraint1 == false.
>>
>> The reason constraint1 == false was:
>>
>> a)    j->limot1.fmax == 0
>>
>> and
>>
>> b)    testRotationalLimit() was not getting called on the first
>> constraint, because limiting1 was == false.
>>
>>
>> The reason limiting1 == false was that the j->limot1.lostop and
>> j->limot1->histop both had rubbish values in them (1.#QNAN00)
>>
>> Now I thought Id put a bad joint into this function, so I checked the
>> input in QuickStepper()
>>
>> At the top of Quickstepper, a pointer to some dxJoints are passed in
>> (*_joint) of length nj.
>>
>> Then a copy of these joints is made by the lines:
>>
>> dxJoint **joint = (dxJoint**) alloca (nj * sizeof(dxJoint*));
>> memcpy (joint,_joint,nj * sizeof(dxJoint*));
>>
>> this being an allocation of some memory for a dxJoint class array of nj
>> length, and copying a number of bytes the length of the size of a dxJoint
>> times the number of joints.
>>
>> now some of these joints could be derived classes of dxJoint, such as
>> dxJointUniversal, which take more memory? dont they? Since
>> dxJointUniversal have extra members such as  limot1 and  limot2
>>
>> so the 2 lines above may or may not be allocating enough space for the
>> joint array that is passed in?
>>
>> and the mem copy may not be copying all of the joints members because the
>> joints are not pure dxJoints, but dxJointUniversals which will have a
>> larger sizeof(), and therefore need more memory copied.
>>
>>
>> Then when universalGetinfo1() is called, the dxJointUniversal pointer
>> passed in is actually a pointer to the copy of the original joint, which
>> was assumed to be of dxJoint size, and may not have been allocated or
>> copied correctly in quickstepper.
>>
>> This could be the cause of the j->limot1.lostop and j->limot1->histop 
>> both
>> having rubbish values in them (1.#QNAN00)
>>
>> Is my reasoning correct?
>>
>>
>>
>>
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Patrick Enoch" <Hendrix_ at gmx.net>
>> To: <ode at ode.org>
>> Sent: Wednesday, June 27, 2007 12:27 AM
>> Subject: Re: [ODE] Problems in QuickStep
>>
>>
>>> Hi,
>>>
>>> yes, looks okay to me now, too :) I completely overlooked those lines
>>> checking for the "fmax" variable in getInfo1. Nothing needs to be
>>> fixed. Thanks for reviewing!
>>>
>>> Patrick
>>>
>>> On 26.06.2007, at 15:23, Remi Ricard wrote:
>>>
>>>> Hi Russel,
>>>>
>>>> You should state which version of ode you are using or even better
>>>> which
>>>> revision of the joint.cpp file you are refering to.
>>>>
>>>>> I had a problem in the function QuickStepper that I think might be a
>>>>> memory overwrite bug. I could be wrong tho.
>>>>>
>>>>>
>>>>> At the top of Quickstepper, the number of constraints are
>>>>> calculated and
>>>>> put into the variable m.
>>>>>
>>>>> Each joint is quizzed on the number of constraints via the function
>>>>> getInfo1()
>>>>>
>>>>> Now I've only been testing this on Universal joints, so it may be
>>>>> different for other joints.
>>>>>
>>>>> The getinfo1() function on a universal joint maps to
>>>>> universalgetinfo1()
>>>>>
>>>>> Inside of this universalgetinfo1() function the number of
>>>>> constraints is
>>>>> filled out into the dxJoint::Info1.m variable.
>>>>>
>>>>> This value can be from 4 to 6.
>>>>>
>>>>> it starts at 4, and  If (j->limot1.fmax > 0) and hence
>>>>> (constraint1 ==
>>>>> true) it will be incremented by 1
>>>>>
>>>>> If (j->limot2.fmax > 0) and hence (constraint2 == true) it will be
>>>>> incremented by 1
>>>>
>>>>  From revision 1108 to HEAD (I did not look before that)
>>>> You have the m increased if limot1.fmax > 0 or there is limits and the
>>>> angle is outside the range for this motor.
>>>>
>>>> Same thing for the second motor.
>>>>
>>>> So it is not only increased if fmax > 0
>>>>
>>>>>
>>>>> then later on in QuickStepper, the function joint->getinfo2() is
>>>>> called,
>>>>> which calls the function dxJointLimitMotor::addLimot() twice.
>>>>
>>>> Yes,
>>>>
>>>>>
>>>>> This function modifies the values in the joint based off the row
>>>>> index
>>>>> passed in, which in the first call to dxJointLimitMotor::addLimot
>>>>> () row
>>>>> equals 4. The first call returns a value to indicate if more rows are
>>>>> needed, which is used by the second call to addlimot() as the row
>>>>> index
>>>>> to update.
>>>>
>>>> The value returned by addLimot does not indicate if more rows are
>>>> needed. It only tells that this row was used. So the next call to
>>>> addLimot should fill the next row if the first call to addLimot fills
>>>> the row 4.
>>>>
>>>>>
>>>>> The criteria to work out how many rows are needed inside of
>>>>> addlimot()
>>>>> are based off wether the (limot.fmax > 0) AND wether the
>>>>> limot.limit is
>>>>> non zero.
>>>>
>>>> The value limot.limit is set in testRotationalLimit and it indicates
>>>> which limit is not respected.
>>>> limot.limit = 0 ( both limit respected)
>>>> limot.limit = 1  lostop not respected.
>>>> limot.limit = 2  hitstop not respected
>>>>
>>>>>
>>>>> This is different to the original calculations of how much memory
>>>>> would be required by the earlier calls to universalgetinfo1().
>>>>
>>>> For me everything looks OK.
>>>>>
>>>>> This means that occasionally these criteria would be different, and
>>>>> underestimate the required memory needed from the getinfo1()
>>>>> function.
>>>>> This resulted in the calls to addlimot() modifying memory after the
>>>>> allocation (which in this case I believe would be the jb array?)
>>>>>
>>>>>
>>>>> I modified getinfo1 to calculate the m value based off not only
>>>>> the fmax
>>>>>> 0 test, but also the limit != 0 test. This seemed to fix my bug.
>>>>>
>>>>> Is this a bug that has been in ODE for a long time that needs to be
>>>>> fixed or have I made a mistake somewhere?
>>>>
>>>> Need more info on the version you are talking since for me the code I
>>>> look at seems OK.
>>>>
>>>>
>>>> Remi
>>>> _______________________________________________
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>>>
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>>
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