Re: low cost stepper driver

Hi,

I'm not sure what your question is in regards to, but an encoder attached to a servo motor is usually run at +5V. While it might be possible to disconnect the encoder while it is powered up and not sustain any damage, you should power down the voltage to the encoder before connecting or disconnecting it it.

A servo motor and its associated encoder can be used in conjunction with an appropriate servo motor controller to provide controlled motion, similar to a stepper motor and drive combined along with a step source.

Not sure if that answers your question or not.

Jeff

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Nelson Collar <nel2lar@...> wrote:
>
> Jeff
> Can the coder be disconected from a servo, or how and what can I use servo motors for? Thanks for any info.
> Nelson Collar
>
>
> ________________________________
> From: jeffalanp <xylotex@...>
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: Tuesday, June 26, 2012 2:54 PM
> Subject: [CAD_CAM_EDM_DRO] Re: low cost stepper driver
>
>
>
>  
>
>
>
> Hi,
>
> A monolithic stepper drive chip like the Toshiba or an Allegro chip will have an absolute maximum voltage rating. A voltage above this and the chip can easily be destroyed, instantly. If the manufacturer of the chip rates the device at a maximum of 35VDC, then it is best to de-rate this value by 15 to 20 percent (or more) for a safer *running* maximum value, i.e. closer to around 30VDC. While the drive can handle voltages up to 35VDC, all day long, no problem, there are events that can occur that can cause the voltage to rise above the max. of 35VDC (if the present running voltage is at, or near 35VDC) such as a rapid motor deceleration, or if using an unregulated power supply, a voltage surge due to things like equipment (compressors) turning off. Starting with a lower voltage than abs. max. with a built in safety margin is the first step to make the system more robust.
>
> Another event that can cause an over-voltage condition is a motor disconnect while the motor is running. A powered disconnect can cause current built up in the motor coil to discharge rapidly creating a high voltage that can destroy the chip. A lot depends on the amount of current built up in the coil at the time of disconnect. If the coil was minimally charged, the chip may actually survive the disconnect. But you never know what state the coil is in, so never connect or disconnect a motor with power on. This means building your system with secure connectors that will not come easily unplugged.
>
> Another thing that can cause over-voltage is static discharge. Walking across carpeting can build up thousands of volts in a human, Then touching the drive, or even wires leading to the drive, allow a path of discharge of the thousands of volts instantly destroying the chip. Lightning discharges can also have the same effect, even if the main bolt is quite a ways away. One of the most common over-voltage conditions in a running wood router system is caused by using an ungrounded vacuum system. An ungrounded vacuum system can create thousands of volts, very much like a Van De Graaff generator. Dis-similar materials like wood dust and plastic hose create a voltage due to something known as the triboelectric effect. The triboelectric effect can be used to create voltages high enough for X-rays to be generated, or drive linear accelerators, so keep those dust collection hose grounded.
>
> An over-current condition can also destroy the drive chip. If the drive chip is rated at 2.5A, then it should not be continuously run at that level without adequate cooling. The amount of current the chip can handle is mainly a function of how much heat can be removed from the chip. A 2.5A rated chip being run in a cool oil bath can conceivably be run at 3.0A or even higher. Barring special cooling like that though, it is best to run at or below the maximum rating. You should be able to run at the maximum current rating as long as adequate cooling is provided. A good heatsink and active cooling such as a fan moving cool air over the heatsink is often enough to handle dissipating heat from the chip.
>
> The main over-current condition that destroys chips isn't running a chip over its rated current level though, it's trying to run the chip with a short. A motor wire connected to the wrong phase or to ground can cause a huge current surge before the chips internal circuitry can turn off the internal transistor. This can instantly destroy the chip. If a system is properly set up to start with, with no stray wires that can cause a short, and no mis-wires, then this type of fault will not generally happen. This is where close attention at setup time becomes crucial.
>
> In almost all hobby systems, setup time is the time when things happen that will destroy the drive. For example running the motors on the bench before installation is a common occurrence. But this can lead to the motor slowly drifting off the desk due to vibrations. All the sudden it falls off, pulling wires with it and a disconnect occurs. A high voltage can be created and poof, a destroyed drive. The drive chip functioned perfectly and in spec. It was just subject to abuse. So take special care during setup to prevent accidents that can destroy the chips. Inspect, and double check all connections for stray wires or mis-wires.
>
> It has been mentioned that monolithic type stepper motor drives are better suited for smaller devices like printers, etc. While the chips are well suited for printers and such, once a small CNC system is set up, and running with voltages in a safe area, with good connectors, and sound wiring, and adequate cooling, the drive system can last years and years, just like it would in a printer. It really comes down to running the chips and its associated system in its safe-operating-area.
>
> Jeff
> www.xylotex.com
>
> --- In mailto:CAD_CAM_EDM_DRO%40yahoogroups.com, "Tony Smith" <ajsmith1968@> wrote:
> >
> > > > has anyone used these ? are any of them any good ?
> > > >
> > > > Dave
> > > Yes! Stay away from the blue ones with the Toshiba chips. They are total
> > junk.
> >
> >
> > The Toshiba chip is the TB6560, or the older TB6550. The main problem with
> > those is they claim to support 36v (max 40v?), and then go bang when you try
> > it. Sticking to 24v seems to work.
> >
> > There's a few versions of those boards, as well as the chips used. A
> > commenter on one of the cnczone thread found his problem was with the
> > optocouplers they used, a later revision didn't have this problem. It's a
> > real YMMV situation.
> >
> > I've got a few of the single motor drivers (rated 3A). These are about $25
> > each on eBay, so it winds up being more expensive than a single 3 or 4 axis
> > board. I noticed those boards now come in an aluminium case (heatsink
> > replacement?), possible an new revision of the internals as well.
> >
> > I figure having individual drivers is a bit more flexible, and if one axis
> > does goes bang I can easily swap a new (possibly better) one in. I also
> > only run them at 2A, for 3A I use the 4.2A version. I dislike running
> > things at their rated spec, mainly because that's usually the peak value.
> >
> > Geckos will give better performance and be more reliable, but are also 3
> > times the price.
> >
> > Tony
> >
>
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