This will not read 5 volts. You may not read anything depending on the device in the PWM cable since it would be pulled up in the Victor by the internal power supply and opto coupler.
The PWM Signal Driver cable that the OP said he was using gets its power from the receiver via the red wire1. The signal driver cable then sources the current required to drive the Victor’s PWM input2.
@DBFIU: If you aren’t getting a voltage signal at the Victor end of your PWM signal cable (as described in earlier post), check to make sure the cable is getting power from the receiver.
1 http://www.ifirobotics.com/victor-883-speed-controller-robots.shtml
2 Robot MarketPlace - IFI VEX Pro 36 Inch PWM Signal Driver Cable
thanks for the help guys it is greatly appreciated… i am going to test my reciever and cables right now.
A run-of-the-mill digital volt meter connected between signal and ground on the output end of the PWM cable sending a standard Victor spec signal (from a cRIO) will read:Neutral = .75v
Forward = 1.0v
Reverse = .5v
The meter reading isn’t bothered by the pulsed nature of the PWM signal.
(These voltages are as measured)
P.S. Joe reminded me that the IFI signal voltage was lower, and I’d assume that the signal driver cable would mirror those lower voltages that Joe listed.
However, the PWM voltage I measure off an old pBasic IFI controller has neutral at .32v, rather than .375, so some variation between controlling devices should be expected. If the OP measures the signal cable output, please post the voltages you get for our future reference.
(For completeness for those robotics teams wanting to measure this on a cRIO, a Jaguar range signal will read:Neutral = 1.49v
Forward = 2.29v
Reverse = .67v
I couldn’t find a spec anywhere for the period of a “standard Victor spec signal”.
Is it 20ms period with 1ms, 1.5ms, and 2ms pulses at 5v for reverse, neutral, and forward? And is this what the OP’s Futaba 6XAS is sending?
If so, and assuming that the voltmeter on DC setting responds to the algebraic average of a PWM signal, then one would expect the meter to read (2ms/20ms)*5v = 0.5 volts at full forward.
On the other hand, if the meter on DC setting responds the the RMS of the signal, then one would expect the meter reading to be sqrt(2/20*25)=1.6V
The attachment shows what the parameters are for the IFI system, the cRIO when used with a Victor, and the cRIO when used with a Jaguar. I suspect the Futaba system would be the same as the IFI system (20ms period).
To toss out another idea, the Victors themselves have been damaged in some fashion. Hopefully this isn’t the case, but did you recalibrate the Victor successfully, or did it fail (that is, did the LED change colors appropriately?) You can check the procedure and the colors that you should see here.
Thanks, Mark.
I think the measured IFI signal voltage is lower (than the signal from the cRIO) lower because the IFI period is longer. They both have 5v pulses.
If you look at the chart Joe posted, the following formula holds true for all 3 columns:
S = W/L*H
where:
S is the measured (with a voltmeter) output signal voltage
W is the ontime (pulse width)
L is the period length
H = 5v is the height of the pulse (pulse voltage)
the PWM voltage I measure off an old pBasic IFI controller has neutral at .32v, rather than .375, so some variation between controlling devices should be expected.
That seems reasonable. The measured (with a voltmeter) output signal voltage “H” would be affected by tolerances off all three terms on the right, as follows:
∆S = (H/L)∙∆W + (W/L)∙∆H - (H∙W/L2)∙∆L 1
Since you already have a testbed setup there, if you have the time and inclination an oscilloscope trace would reveal which of the three terms is making the largest contribution to the difference.
1 This is derived from the above formula S=W/L*H for the algebraic average of the signal. I wonder if all voltmeters respond precisely to this metric. If not, that could be an additional reason why the measured voltage differs.
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Hello all,
Thank you so much for your insight. I have since replaced my 15 year old futaba controller, it was the main cause of the problem. The Vic was not getting a PWM signal. I have a new controller and it delivers a proper strong PWM signal.
Now there is a new problem. I have a small 550 mabuchi size brushed motor in my RC car. This thing pulls maybe a 60 amps with this 7.2v nimh pack. It is hooked up to my vic 883 and my new controller. If I floor it, it STUTTERS badly.
I calibrated the vic, got the green light for a good calibration. So that worked out. But the stuttering is occuring in both forward and in reverse.
If I dont floor the throttle, it wont stutter. If I pull gradually into throttle it wont do it, only when I got wide open throttle. It might be a large current surge, but how on earth can this little motor affect the vic 883? I used to put close to 200 amps through this vic NO PROBLEM. I dont think it is a current carrying capability. I am not sure where the stuttering problem is coming from now.
Please help if you can,
Thanks
- D
Is the battery protected in some way? What you describe sounds like a protection device cutting in at high currents. Do you have a breaker installed?
If you’re only supplying 7.1 volts, a quick increase in current could be pulling the Victor’s input voltage down to the point where it doesn’t work properly. Are your supply wires dropping too much voltage because they’re too long or too high a gauge?
or poor connection quality? as in bad crimps or the like?
also look for wire damage…
All valid points and I think you are all right.
Remember, this victor is used to seeing 12-24v. I am using a 7.2v pack with no cutoff or breaker, its probably pulling 60 or so amps so the voltage is dropping below 6v which I believe it minimum for victors.
I will put another pack in parallel to see if it solves the problem, I anticipate that it will.
I am sorry, the Victor will not work reliably at 7 volts. The internal voltage regulator will drop out at near that input voltage.
Hello everyone,
Thank you all for the suggestions.
Here is where I stand.
I wired two 7.2v nimhs in series for a 14.4v pack. Powered the victor, it ran fine for a few minutes, then it started to do the power cutoff thing again. This was literally 60 seconds from when I started driving around under LIGHT throttle. Literally couldnt have been more than 50 amps I was pulling in very short bursts. The voltage could not have possibly dropped from 14.4v down to 6v because of a 50 amp pull, that just doesnt sound right.
After I took the car back inside, I inspected it, couldnt see anything wrong. I think the wire gauge is a little on the thin side, but it didnt even get warm so I dont see how that could have had an effect within window of just 60 seconds or less.
The power cutoff is strange and it is starting to aggravate me to no end!!!
Not sure what else to do, maybe get thicker wire? Better joints? The joints are regular crimp on lugs and the wire is 18 gauge.
DB,
I think it is telling that you ran for almost a minute before problems started. What are the ratings on your 7.2 volt battery packs? There should be something rated in AH or maH listed onthe batteries label.
Hello,
Thank you for all the help. I figured it out.
I fully charged my batteries and re crimped the connections and it ran fine. The voltage drop was attributed to one of my batteries not having a full charge and the other was charged.
When I was charging the batteries I did them in parallel and for some reason one of them might have gotten lose and the charger showed that it peaked but it really wasnt fully charged.
The car ran great and it really screams on 14.4v!
Thank you guys!
Consider that a confirmation of the typical advice not to charge batteries in parallel like that. Unless you’ve always kept the batteries in parallel, so that they have experienced the same conditions throughout their life, you’re likely to have problems. For example, one battery might charge first and fool the charger into shutting off before the other one has gotten a significant charge.