Hey everybody. does anybody happen to know when FIRST allowed teams to use victor 883’s? I know they did at one point, because we had some lying around the shop.
The reason I ask is, I am looking for 2 of them that I could possibly buy from another team for less than IFI’s $150 price tag, so that I can use them in a custom project. At least if I know when they were legal, I know which teams would possibly have some that they no longer need.
Any help would be greatly appreciated.
1999 to 2002 as I recall.
The 884’s were introduced in the 2003 season.
Email David Bodmer at [email protected]
I know we have a few on our practice bots and I’m sure we can spare a few.
.
Why thank you. Both of you. Sending out an email now!
Keep in mind the FIRST 883’s do not handle above 12V like the ones available from IFI do (fairly certain of this).
I’ll check this out tonight with the 1 that I do have. I know that the 884’s and the 883’s both accept input voltage of 24v, and that the 884 regulates it down to 12v output. I just never bothered to check that of the 883
I just checked with an 883 that was plucked off one of our older FRC bots, and put on a vexbot, and it does indeed output at 24v.
Interesting, that is very good to know!
I’m trying to figure out what made me think that years ago…
OK,
The old 883 and 884 may output 24 volts but they are not designed for that voltage. The breakdown on the FETs is too low. There are a few minor differences between the two. The 883 needs a transorb attached to the power input, the 884 has an internal one included. There was a production run of “blue” 883 which were the preproduction of the 884. I believe another significant difference is the inclusion of the dead-band in the 884 to quiet the output with noisy joysticks.
Please note that the IFI/VEX site has part numbers for the new 883, 884, and 885 controllers which are available in 24 volt versions and available with either 24 or 12 volt fans.
Actually, I believe the 883 had a 10% dead-band, while the 884 lowered that to 3%.
Joe,
I am thinking that was the 883 “blue” but I have not found that documented in my files yet.
Sorry to go a little off-topic, but what exactly is a “dead-band?”
Thanks.
It’s an area around zero (typically) where changes in the input produce no change in the output (output typically stays at zero in the deadband).
For example:
y = zero if -delta<=x<=delta (“deadband”)
y = m(x-delta) if x>delta
y = m(x+delta) if x<-delta
~
Akash,
The deadband is a software/firmware defined zone where the output remains disabled. The Victor is at neutral with a 127 value on the input PWM. From the IFI Programming Guide:
PWM Speed Controller Full Forward = 254-227 Neutral = 136-123 Full Reverse = 0 – 37
Joystick Y Axis Full Forward = 254 Neutral = 127 Full Back = 0 – 25
Joystick X Axis Full Left = 254 Neutral = 127 Full Right = 0 – 25
Joystick Wheel Full Forward = 254 Neutral = 127 Full Back = 0 – 25
The dead band is the neutral 136-123 value. These values were needed as typical joysticks would never return to the same value when the joystick was released (return to center). By including the deadband, anywhere near the center would cause the Victors to stop. Since the neutral position is also sensed for “brake” mode, it was essential for that operation to produce a neutral PWM output when the joystick was released. Used joysticks still have problems in that there is considerable overshoot when you let go from a full throttle position due to wear of the mechanical components. Since many teams are using hand held controllers, the problem is not nearly as bad as with a full up CH control stick as was provided in the KOP in the past. Joe may have a better handle on this, but I think the deadband was able to be modified in the robot code.