Speed Controller brake/coast setting

[steven114]

Is it possible to control the brake/coast setting on the 884s with the digital out pins? I didn't want to try anything, as I believe a 1 is +5v. Will I damage anything by using this to select between brake and coast on the fly?

Thanks,
Steven

[Kevin Sevcik]

I have no idea about the actual anser to your question, but when don't you control it with a relay? I'm fairly certain that would work, though not a spike relay.

I say get a miniature 5V relay, hook the coil up to the digital output, and hook the other side up to the brake/coast jumper. I'm assuming this will work, except I have no clue how much current the digital outputs can supply on the signal pins. Or even if that's how they work. IFI doesn't have much information on digital outputs on the website. The realy should work, however, as FIRST talks about using a microswith to control the brake/coast setting.

[KenWittlief]

I dont know the correct answer, but I would not connect them to the digital output pins

try searching the forum, im sure someone has done it before - seach on 'victor brake' and see what comes up

[Biff]

A dip relay would do the trick for the "jumper" side, The current the coil draws is a published thing and a long time ago they were avialable from Digi-key. I would talk to the folks at Innovation First If the digital outs can sink the current. If you get dip relays get the ones with internal diodes, without diodes, the back emf can fry things, else put a diode as clsoe to the coil wireing as you can. If all is a go in terms of the rules you may have to use a driver transistor to keep the current to what the controler can do, OR Use a spike with diodes like called out in the <5.6.3> to drive two relays and avoid the whole asking permission about hooking directly. Also the information you seek may be in the user guide for the full size controler. Good luck

[KenWittlief]

if the rules allow it, the easiest thing to do would be to have a contact switch that you close with one of the little servos they gave us.

[jacob_dilles]

yeah and if your not into servos and contact swiches.... just get a 5v dpdt relay, hook it up to (1) digital output and *vwala* perfect switching. the Victor 884 uses a pic microprosseser to control the fets in the HBridge, and its not going to be exsessive current at all. just remember to put it all in a box

[velocipenguin]

The officially-sanctioned method, as suggested by IFI in the Victor 884 User's Guide, involves using servos and SPDT switches. I'm not sure if there are other methods that would be safe and successful, but that seems to be the one they encourage.

[jacob_dilles]

okay.

servos are $30 bucks each. relays are free.
servos and switches are exsesivly prone to failure.
servos eat up power...
servos are huge compared to relays.

with all that said, yes its the "offical" way to go. will our team do it? uh no

[velocipenguin]

I'm not saying that other methods are wrong. I'm just saying that the servo method is the one suggested by IFI.

For the record, you can draw 1 ampere total from all of the analog output and digital I/O Vcc pins. If you're not powering a lot of other stuff from those, using small relays should be fairly safe.

[Al Skierkiewicz]

The suggested method is one we have used over the years. A servo with the cross attachment is mounted in such a way that when it turns it bumps into a microswitch that is wired across the brake pins on the speed controller. Controlled from software the servo either closes the switch or opens it.

[Kevin Sevcik]

The servo method does have one thing going for it. The servo should stay in position after power is cut to your robot. I think. I'm not an electronics guy on the robot, but if the power to the servo gets cut then it will definitely stay in position.

[KenWittlief]

where do you get these free relays from?

I will take 10 million please :c)

if you are talking about the relay spikes that are in the KOP - you cannot use those to control the brake pins - the spikes put out 12V switched plus or minus, and they need power on their input (+12V) to work. they dont get their power from the PWM cables.

[Phil_Lutz]

Originally Posted by Kevin Sevcik

The servo method does have one thing going for it. The servo should stay in position after power is cut to your robot. I think. I'm not an electronics guy on the robot, but if the power to the servo gets cut then it will definitely stay in position.

The Servo will not move if there is no force applied to it on power-down.
We are using a servo to hold a brake mechanism for our winch. When power off occurs, the spring tension will rotate the servo to a non stressed position.

For the purposes of activating a switch, the servo will not be "loaded' and therefore work for you.

Phil

(PS. I fly R/c planes and gliders so I know servos

[The Lucas]

Originally Posted by steven114

Is it possible to control the brake/coast setting on the 884s with the digital out pins? I didn't want to try anything, as I believe a 1 is +5v. Will I damage anything by using this to select between brake and coast on the fly?

Thanks,
Steven

This question was answered in the Q&A today (ID: 893):

Q: Can a digital output of the Robot Controller be connected to the B pin of the Brake/Coast selector on the Victor 884 in order to control the Brake and Coast functions of the Victor?
A: No. There are possible ground loop problems associatedwith this approach.

Unfortunately, the answer is no. You can’t legally wire a digital out to the Victor, but it might work. Ground loop problems are tricky and usually produce noise. They usually occur in audio/video systems.

You could probably stare at Victor 884 and RC schematics for hours debating about whether a ground loop problem would exist. Basically, the digital out current leaves the RC and must return to ground through the Victor (instead of the RC), thus creating a ground “loop”. This could possibly be solved by connecting the ground pin of the digital out to the A pin (which is grounded) of the Victor, but this depends on the internal wiring of the Victor and could produce problems of its own. It really doesn’t matter. FIRST said we can’t use this method and that is all that matters.