Re: Is it okay to run one motor in a two motor transmission?
 

I'm not so sure about this. It may be all electronically operated but there is definitely something in there that makes a noise when operating (as far as I know) correctly. Everytime we've "triggered" a properly working spike on my team we've heard it click. One interesting thing is this relay is listed as solid state whereas the Spike is not. But I don't know anything about H-bridges so I have no clue.

Re: Is it okay to run one motor in a two motor transmission?
 

If I can remember, I will open one tonight. Are you still using one of the old Spike modules from a few years back? Those were relays as I remember. The "H" bridge is the same as is used in the Victor, effectively it is four switches only two of which are turned on at a time. Think of a capital H where the motor (or load) is the crossbar and the four switches are the lines above and below the cross. The top of the H is connected to battery + and the bottom is connected to battery -. If the upper left and lower right switches close, then the motor sees current flow in one direction and turns forward. If the lower left and upper right turn on then current flows through the motor in the opposite direction and the motor reverses. If both the bottom left and right switches turn on then there is a closed loop to battery - shorting out the motor for "brake". If all switches are open then no current flows and the motor "coasts".

Re: Is it okay to run one motor in a two motor transmission?
 

Al did a good job of explanation. Here is the spec sheet for an H bridge driver I was designing into a product some time ago: http://www.st.com/stonline/books/pdf/docs/10386.pdf

This device is made for automotive applications and can switch 30A of DC current. The auto industry uses them to control window motors, seat motors, et cetera.

Re: Is it okay to run one motor in a two motor transmission?
 

Cool!
Under reverse battery protection, many people use a diode reverse biased across the battery input. It will only turn on when reversed and have no forward voltage drop to affect the elctronics. Hook it up backwards and the diode blows the fuse.

Re: Is it okay to run one motor in a two motor transmission?
 

Al and Mike Betts from previous. I think the brake/coast jumper serves the function of the FET at the bottom of mike's schematic, providing a dissipation path for the "reverse emf" or back current of the off but driven motor. I did a quick review of the InnovationFirst docs on the 884/883 victor and the section on the brake/coast jumper talks about using limit switches to do in operation change from brake to coast if the hold feature of brake is desired. In final note. Wouldn't an open circuit present an infinite resistance therefore represent a total current drop. The current would be zero even though the armatuer coils are breaking the magnetic fields inducing electron flow against an infinite resistance. Nough for now. LRU

Re: Is it okay to run one motor in a two motor transmission?
 

This is getting a bit confusing because we are talking about both Spikes and Victors.

First of all the Spike does not have a brake.

A brake is usually an active control where both lower side FETs are turned on (LSa and LSb) and both uppers (HSa and HSb) are turned off. When EMF is produced by the motor (acting as a generator) one of the two lower FETs would conduct and the opposite FET's anti-parallel diode completes the circuit giving the short circuit.

This same effect can be made with a N.O. relay across the output. It has the benefit for FIRST robots of continuing the brake action after power is removed. I believe that IFI uses the relay method.

I believe the FET at the bottom on that H bridge diagram is to give an active clamp across Vcc is the input voltage is reversed. The FET is turned off if Vcc is normal or if Vcc = 0.

Re: Is it okay to run one motor in a two motor transmission?
 

Okay wait,

Putting aside the mechanical vs. solid state debate aside... I know it was stated that as long as the victors are jumpered for "coast", i could have the motor spin freely without having to worry about some catastrophic detonation somewere down the line between the motor and the battery. Or will I? I have some itchy feeling that if I had only one of two motors in a dual motor gearbox running, the other motor (non-powered) will somehow generate enough current to cause the victors to transform into a fried $100 dollar paper weight...

Re: Is it okay to run one motor in a two motor transmission?
 

No. That will not happen. As long as you have the coast jumpered and the backdrive pins defeated, you will be OK...

Re: Is it okay to run one motor in a two motor transmission?
 

Ok, thanks.

Re: Is it okay to run one motor in a two motor transmission?
 

Larry,
The limit switches mentioned in the IFI docs are simply a microswitch with contacts wired to the brake/coast input on the Victor. A servo is then used to energize the microswitch giving complete control over brake. We have used this method many times in the past. As to the infinite resistance question, you are correct, no current flows when the coast jumper is selected. With no current flow, there is no way for the current in the armature to develop back EMF (Electro Motive Force) and therefore no opposing force to movement coupled to the armature. Mike's schemo is a device he was working on, not the IFI device. The Victor does not have a relay in the output and no low side FET in the common lead.
As a side note to everyone, a reminder actually. Victor circuits are open to the outside world to allow cooling air to flow. Metal chips can and do fall into the Victor and permanent damage is the result. When working on your robots, make sure all metal chips are removed first and cover the electronics with a drop cloth when you drill on the robot.

Re: Is it okay to run one motor in a two motor transmission?
 

I opened one of the Spike Blues last night. The black box sticking up is where all the power is modified. It has several pins on it but not enough to be individual relays. It is a sealed box none the less. I think IFI will have to give the answer on this one. It could be a special relay or solid state device.

Re: Is it okay to run one motor in a two motor transmission?
 

For those interested, the following link has a good discussion
on H-Bridge circuits of both the relay and solid state type.

http://www.dprg.org/tutorials/1998-04a/

Re: Is it okay to run one motor in a two motor transmission?
 

Doc,
Very nice find! For those who will read the article, in the final drawings just substitute three power FETs for each of the transistors and you will have the Victor output circuit.