On Mar 16, 7:14=A0am, John Devereux <j...@devereux.me.uk> wrote:
> BillSloman<bill.slo...@ieee.org> writes:
> > On Mar 16, 12:41=A0am,BillMartin <w...@wwmartin.net> wrote:
> >> Hi,
> >> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
> >> recommend for a simple, low performance integrator to generate a volta=
ge
> >> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one =
to
> >> two seconds duration, no repeating..one shot style. Looking at just
> >> Mouser, there seem to be 23 parts in soic-8 to choose from...
>
> > The Linear Technology LT1013 has rather tighter specifications.
>
> Bill, that's a $5 against a $0.05c part. Well, nearly.
>
> He wants cheap and nasty; LM358(a) is it.
>
> If he wants it gold plated he can pay the extra 0.5 cents and spring for
> a LM258A! :)
>
> > The single version - the LT1006 - is a whole lot more tightly
> > specified and quite a bit more expensive again. You might balance the
> > extra cost against the saving on a smaller integrating capacitor.
>
> I doubt it!

Texas Instruments are now second sourcing the LT1013, and that seems
to be a roughly $1 part. Big film capacitors cost that kind of money.

--
Bill Sloman, Nijmegen

Bill Sloman <bill.sloman@ieee.org> writes:

> On Mar 16, 12:41&nbsp;am, Bill Martin <w...@wwmartin.net> wrote:
>> Hi,
>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>> recommend for a simple, low performance integrator to generate a voltage
>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>> two seconds duration, no repeating..one shot style. Looking at just
>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>
> The Linear Technology LT1013 has rather tighter specifications.

Bill, that's a $5 against a $0.05c part. Well, nearly.

He wants cheap and nasty; LM358(a) is it.

If he wants it gold plated he can pay the extra 0.5 cents and spring for
a LM258A! :)

> The single version - the LT1006 - is a whole lot more tightly
> specified and quite a bit more expensive again. You might balance the
> extra cost against the saving on a smaller integrating capacitor.

I doubt it!

-- 

John Devereux

On 3/15/2012 5:20 PM, Bill Martin wrote:
> On 03/15/2012 05:10 PM, mike wrote:
>> On 3/15/2012 4:41 PM, Bill Martin wrote:
>>> Hi,
>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>> recommend for a simple, low performance integrator to generate a voltage
>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>>> two seconds duration, no repeating..one shot style. Looking at just
>>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>>
>>> Thanks,
>>> Bill Martin
>>
>> Since you have no requirements for linearity...or anything else...
>> I'd just use a cap and a resistor.
> That was version 1.
>>
>> The only application I can think of for a device that has "no repeating"
>> is some kind of trigger for something that goes boom.
> Oh, I hope not. It just shuts down due to power being turned off. :-)
>>
>> Precise requirements/specifications are your friend.
>
> Ok, a sort-of-linear ramp is desired. I may then torture that into
> something exponential, but opposite of how r-c time constant works.
> The game is simple: Feed as much power to a small dc brushed motor as
> possible without making the drive "slip". So, the faster it's turning,
> the more pwm I can shove at it without increasing average current too
> much. It's a toy circuit...driving a 1/24 scale electric dragster.
>
> Bill
>
PWM power supply chip with soft start?
Feed output back to soft start circuit?

If the drive "slips" make a better drive.
If you mean "wheels spin", can you do something
with a position sensor on the suspension?
Maybe a spring on a wheel out the back that
detects a "wheelie" and reduces the current?
That'll give you optimization for the current
track conditions.
Having the front wheels on the ground, especially
if they're doing any steering, is just a waste
of energy.  ;-)

On 03/15/2012 06:33 PM, Tim Williams wrote:
> If you want to limit torque then you want a constant current drive. Set
> it to just below the point of slippage then let it go.

This is very much the idea here. Full traction control would be nice, 
but not really needed to be better than what's out there now in way of 
motor control.

> One can easily be made with an LM393 triangle generator + PWM comparator
> and an LM358 half as the current feedback error amplifier. The setpoint
> can be constant, or controlled from a second error amplifier to control
> speed or voltage or some other variable.
>
> Tim
>
Version 1 does pretty well with just an r-c curve to control the pwm 
ramping up, but it's really not the right shape for the ramp. Backwards, 
actually! pwm is done by a nifty little chip from Supertex, meant to be 
controlling cooling fans in electrical racks. Darn thing comes Soooo 
close, but doesn't quite do everything needed.

Bill

On 03/15/2012 06:59 PM, Jamie wrote:
> Bill Martin wrote:
>
>> On 03/15/2012 05:10 PM, mike wrote:
>>
>>> On 3/15/2012 4:41 PM, Bill Martin wrote:
>>>
>>>> Hi,
>>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>>> recommend for a simple, low performance integrator to generate a
>>>> voltage
>>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About
>>>> one to
>>>> two seconds duration, no repeating..one shot style. Looking at just
>>>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>>>
>>>> Thanks,
>>>> Bill Martin
>>>
>>>
>>> Since you have no requirements for linearity...or anything else...
>>> I'd just use a cap and a resistor.
>>
>> That was version 1.
>>
>>>
>>> The only application I can think of for a device that has "no repeating"
>>> is some kind of trigger for something that goes boom.
>>
>> Oh, I hope not. It just shuts down due to power being turned off. :-)
>>
>>>
>>> Precise requirements/specifications are your friend.
>>
>>
>> Ok, a sort-of-linear ramp is desired. I may then torture that into
>> something exponential, but opposite of how r-c time constant works.
>> The game is simple: Feed as much power to a small dc brushed motor as
>> possible without making the drive "slip". So, the faster it's turning,
>> the more pwm I can shove at it without increasing average current too
>> much. It's a toy circuit...driving a 1/24 scale electric dragster.
>>
>> Bill
>>
> How do you plan on detecting if it is slipping or not?
>
> Going to have a generator reference on the front wheels?
>
> Jamie.
>
>
It's not going to be that advanced. I would have to mount the board on 
the "moving parts" to really do traction control. Just doing "educated 
guessing", once there is enough run data to tune it up.

Bill

If you want to limit torque then you want a constant current drive.  Set it 
to just below the point of slippage then let it go.

One can easily be made with an LM393 triangle generator + PWM comparator and 
an LM358 half as the current feedback error amplifier.  The setpoint can be 
constant, or controlled from a second error amplifier to control speed or 
voltage or some other variable.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Bill Martin" <wwm@wwmartin.net> wrote in message 
news:jju10m$9ef$1@dont-email.me...
> On 03/15/2012 05:10 PM, mike wrote:
>> On 3/15/2012 4:41 PM, Bill Martin wrote:
>>> Hi,
>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>> recommend for a simple, low performance integrator to generate a voltage
>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>>> two seconds duration, no repeating..one shot style. Looking at just
>>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>>
>>> Thanks,
>>> Bill Martin
>>
>> Since you have no requirements for linearity...or anything else...
>> I'd just use a cap and a resistor.
> That was version 1.
>>
>> The only application I can think of for a device that has "no repeating"
>> is some kind of trigger for something that goes boom.
> Oh, I hope not. It just shuts down due to power being turned off. :-)
>>
>> Precise requirements/specifications are your friend.
>
> Ok, a sort-of-linear ramp is desired. I may then torture that into 
> something exponential, but opposite of how r-c time constant works.
> The game is simple: Feed as much power to a small dc brushed motor as 
> possible without making the drive "slip". So, the faster it's turning, the 
> more pwm I can shove at it without increasing average current too much. 
> It's a toy circuit...driving a 1/24 scale electric dragster.
>
> Bill
> 

On Mar 16, 12:41=A0am, Bill Martin <w...@wwmartin.net> wrote:
> Hi,
> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
> recommend for a simple, low performance integrator to generate a voltage
> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
> two seconds duration, no repeating..one shot style. Looking at just
> Mouser, there seem to be 23 parts in soic-8 to choose from...

The Linear Technology LT1013 has rather tighter specifications. The
single version - the LT1006 - is a whole lot more tightly specified
and quite a bit more expensive again. You might balance the extra cost
against the saving on a smaller integrating capacitor.

--
Bill Sloman, Nijmegen

Tim Wescott wrote:

> On Thu, 15 Mar 2012 16:41:12 -0700, Bill Martin wrote:
> 
> 
>>Hi,
>>anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>recommend for a simple, low performance integrator to generate a voltage
>>ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>>two seconds duration, no repeating..one shot style. Looking at just
>>Mouser, there seem to be 23 parts in soic-8 to choose from...
> 
> 
> Surely you mean 23000.
> 
> The LM358 is still out there, and cheap.
> 
Ha, you got that right!,. I have crap loads of them.

Jamie

Bill Martin wrote:

> On 03/15/2012 05:10 PM, mike wrote:
> 
>> On 3/15/2012 4:41 PM, Bill Martin wrote:
>>
>>> Hi,
>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>> recommend for a simple, low performance integrator to generate a voltage
>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>>> two seconds duration, no repeating..one shot style. Looking at just
>>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>>
>>> Thanks,
>>> Bill Martin
>>
>>
>> Since you have no requirements for linearity...or anything else...
>> I'd just use a cap and a resistor.
> 
> That was version 1.
> 
>>
>> The only application I can think of for a device that has "no repeating"
>> is some kind of trigger for something that goes boom.
> 
> Oh, I hope not. It just shuts down due to power being turned off. :-)
> 
>>
>> Precise requirements/specifications are your friend.
> 
> 
> Ok, a sort-of-linear ramp is desired. I may then torture that into 
> something exponential, but opposite of how r-c time constant works.
> The game is simple: Feed as much power to a small dc brushed motor as 
> possible without making the drive "slip". So, the faster it's turning, 
> the more pwm I can shove at it without increasing average current too 
> much. It's a toy circuit...driving a 1/24 scale electric dragster.
> 
> Bill
> 
How do you plan on detecting if it is slipping or not?

  Going to have a generator reference on the front wheels?

Jamie.

On 03/15/2012 05:10 PM, mike wrote:
> On 3/15/2012 4:41 PM, Bill Martin wrote:
>> Hi,
>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>> recommend for a simple, low performance integrator to generate a voltage
>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>> two seconds duration, no repeating..one shot style. Looking at just
>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>
>> Thanks,
>> Bill Martin
>
> Since you have no requirements for linearity...or anything else...
> I'd just use a cap and a resistor.
That was version 1.
>
> The only application I can think of for a device that has "no repeating"
> is some kind of trigger for something that goes boom.
Oh, I hope not. It just shuts down due to power being turned off. :-)
>
> Precise requirements/specifications are your friend.

Ok, a sort-of-linear ramp is desired. I may then torture that into 
something exponential, but opposite of how r-c time constant works.
The game is simple: Feed as much power to a small dc brushed motor as 
possible without making the drive "slip". So, the faster it's turning, 
the more pwm I can shove at it without increasing average current too 
much. It's a toy circuit...driving a 1/24 scale electric dragster.

Bill