Using Digital Output to control Brake/Coast on Victor

[Neurovirus]

Can a female-female PWM cable be used to connect Digital Output to Victor?
How will you program it to brake and coast using easyC?
and any other thing that I need to know...
Thanks for your help!!

[cardinalman86]

I don't think u can connect a female connector to a victor. I might be wrong, and somebody can correct me if i'm wrong, but in a Victor, normally don't u put the male end into the pwm hole. Then we need to know what program your using to program your robot? It will guide you through the process.

[Jim E]

Yes it can, but we have not tried it.

If your application requires that you have to switch from brake to coast, or vice versa, then try it. Just make sure the control lines are defined as digital outputs and not the default inputs in the IFI code.

I'm not sure how well the brake function works with the victor. My guess would be it will slip somewhat if the motor inertia is too great for the victor to hold.

To program this, you basically need the I/O switch to simulate the jumper being installed on the victor. This may require 2 output lines from the controller. You need to find out about the circuitry inside the controller( pull up resistors, etc.) in order to determine if you pull the pin low to close the switch, or if it is reverse logic. See IFI's website for this information.

Good Luck.

[DonRotolo]

I believe you need to connect a digital output of the RC to the center pin of the Victor "Coast/Brake" connector (which is male on the victor, so you'll need a double-femals PWM cable, but a single-pin cable is all you really need).

Then, set the pin High or Low depending on whether the brake is on or off.

Remember this is dynamic braking: Brake off means "Open circuit" when Victor is at 127, Brake on meand "Short Circuit" when vistor is at 127.

A DC motor acts like a generator - a short will cause the generator load to be high and cause a braking effect. The force depends on the speed of the motor - high speeds generate a lot of power and thus a lot of braking, low speeds generate virtually no braking effect.

Search the forums for more info on both points.

Don

.

[Qbranch]

Also, please remember that all energy has to go somewhere. When the victors ground both sides of the motor, and all that electricity can't go anywhere fast, the CIM will generate a little heat and a TON of electro magnetic field.

Beware: at a high speed, this EM field can be more than intense enough to disrupt analog signals and sometimes even digital signals.

Can't wait to see all the autonomouses this year (especially ours... )

-q

[Jim E]

Thank you Don for the excellent post. That helps clear it up for me.

So having the brake set would mean the battery is drawing a large current into the motor in order to stop it's inertia if running full bore. The victor doesn't see the current path at all since the MOSFETs are short circuited(no damage) or do the Victors sink the excess current?

If the speed is great enough, then there exists the possibility to trip the 40A breakers when the brake is applied?

I need to search the Forums myself.

[DonRotolo]

No batteries involved, The Victor is switched on in such a way as to short the motor terminals together. The MOSFETs have to absorb the full output of the motor(Generator), that energy transfer is the braking action.

The victor input is not drawing any current during braking, and the input side is electrically isolated from the goin's on at the output.

Don

[Qbranch]

Originally Posted by Jim E

So having the brake set would mean the battery is drawing a large current into the motor in order to stop it's inertia if running full bore. The victor doesn't see the current path at all since the MOSFETs are short circuited(no damage) or do the Victors sink the excess current?

If the speed is great enough, then there exists the possibility to trip the 40A breakers when the brake is applied?

No, there is little or no current draw on the battery beyond what the cooling fan on top the victor draws. All that happens is both sides of the motor are tied to ground (bottom two mosfet triplets energized) which causes the motor's back EMF to fight the forward motion of the motor. Note i said EMF: this is what you have to watch out for. It won't pop breakers or anything, but just like a broad-spectrum low frequency RF emitter it'll induce currents in any surrounding signal wires.

-q

[Al Skierkiewicz]

Alex,
You are correct about the back EMF working to brake the motor but the action occurs as the armature windings move withing the magnetic field of the permanent magnets within each motor. Any wire in a changing magnetic field will induce current to flow in the wire. The current flows into the very low impedance of the speed controller when in the Brake mode. As long as the motor is not spining faster than it did when being driven, the EMF generated should be about the same as when controlled. It will of course produce a current flow opposite to that when it is driven by a voltage source. There should be no real increase in generated field than that which occurs with the motor under control. The high instantaneous currents will produce some fields around the motor wiring, and these may interfere with some signal wiring. If you are not using zip type cable (the two wires are bonded to each other and the fields tend to balance out.) then the fields around the wire can be a source of interference. For that reason, do not run servo, sensor or modem cables near motor wiring

[Jim E]

Thanks for the posts.

I had planned on using brake on some Victors this year. Now I know that any sensor wires running close to the motors require special considerations for EMI shielding. That isn't a big issue, but the robot controller is located pretty close to the motors in question. I'm pretty sure there isn't any EMI shielding there (aka. new layout).

[Qbranch]

Originally Posted by Jim E

pretty sure there isn't any EMI shielding there (aka. new layout).

You could also use a lead brick to shield your robot controller if it's bothering you. (lead brick aka battery).

Ok, i'm officially not posting on this thread anymore tonight. (3 posts later...)

-q

[The Lucas]

In this post I describe how I make a brake/coast cable. I do recommend you take the white pin out of the black housing (shrink tube or electrical tape the exposed metal) and plug it into the center pin on the brake/coast header. The 3 pin black housing is too wide for the brake/coast header (it is built for jumpers) and it will not plug in all the way. I also chain 2 victors per digital output. I wouldn't recommend chaining more than 2 victors per output.