If your motor cables are not shielded over that length, I am pretty sure that you are going to get all kinds of strange behavior from your system. The one biggest source of noise is the motor load switching. The noise is a factor of the area between the earth plane and the motor cable (or cables if not twisted). If the cable is screened and correctly earthed, you will minimize the noise but if it is not, you are transmitting it all over the place. I would suggest that you dont waste time and get them properly screened and earthed. The earth is only connected at the source or drive side otherwise you cause an earth loop. . On 2013/01/08 08:03 PM, Viesturs Lācis wrote: > 2013/1/8 Peter C. Wallace <[email protected]>: >> Sounds like you have a severe noise issues, which is not terribly surprising >> with 11M motor cables. >> >> First thing I would do would be to add a common mode choke around the U/V/W >> Motor wires at each 7I39 end of the motor cable: Laird-Signal Integrity >> Products 28B1122-100 is a good choice here. > Ok, I will try to find some place, where to obtain ferrite rings. One > shop did not have them, the others were already closed, so I will try > them tomorrow morning. I guess that visiting places that fix different > electronics stuff also might work - they might have something to pull > these things out, so I will try my luck finding some of them as well. > >> Another thing to do is increase the encoder filtering if you have not already >> done this: >> >> See the hostmot2 manual page, raw mode section (you need to enable >> raw-mode) >> >> Don't know if there's a HAL example of using raw-write but here's an >> approximation: >> >> setp hm2_[HOSTMOT2](BOARD).0.write-address 13312 # (0x3400) >> setp hm2_[HOSTMOT2](BOARD).0.write-data 8 (divide/10) >> setp hm2_[HOSTMOT2](BOARD).0.write-strobe TRUE > I added enable_raw to config string right after number of encoder > modules to be loaded in top of ini file and copied the above 3 lines > in main HAL file. The thing is that I receive error message that pin > hm2_5i23.0.write-address is not found. I tried also write_address > instead of write-address, but still the same. Any ideas? > > The encoder has 4000 PPR and motor will not spin faster than 50 > revolutions per second, so that is 200 kHz max count rate. I guess > that adding a little safety margin would be smart, so what write_data > value I need to set filter time constant at 6 usec? > > > >> Other things >> >> Shielded motor wires > Not implemented. I did not find any 4-lead multistrand wires with > shielding, where each lead would be at least 0.5 mm^2. So I went for > unshielded 0.75 mm^2 4-lead wires. > > What is the idea behind it? To prevent noise being induced in motor > wires or to keep noise being induced by the current in motor wires? I > mean - keep the noise out of motor wires or keep it inside and not let > out? > >> shielded encoder cables (differential signals on twisted pairs) shield >> terminated at 7I39 (differential adapter) end and open at motor end > Both of them are implemented - encoder signal is differential, cable > is shielded, connected to ground on a clamp right on case of control > box - that is the point, where all the ground wires meet. > > >> Forgot to say: the Hall wires should also be shielded >> and since they are single ended you may need to add a >> .1 uF capacitor from each Hall pin to Gnd at the 7I39 end >> of the cable > It already has a shield - they are share the same cable with encoder signals. > I will try to find a place to obtain capacitors. > > > 2013/1/8 Bruce Layne <[email protected]>: >> The first thing I'd do is get a digital storage >> oscilloscope and observe all of the signals - motor power, Hall effect >> signals, encoder signals, any control signals. > I have been thinking about purchase of oscilloscope for a long time. > So far their pricing have seemed too much for me, so I have not > obtained it and unfortunately have insufficient funds to do it now. > Thanks for the reminder though! I guess that having oscilloscope would > allow me to see, where exactly the noise is - is it hall signal, > encoder or whatever else... >
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