jumper cabling from sensors to controller

[Gary Dillard]

This is a follow-on to my thread about 3-pin pwm connectors; I looked through the threads on wiring recommendations and didn't see anything that specifically addressed this....

I am tasked this year with improving the integration of our controls system from a physical hardware standpoint. One of the things that seems to hold us up is cable routing, especially to the sensors. Last year we did a great job cleaning up the power cable routing (love the new relay board), but running small wiring to all the sensors is always the last thing we do. It seems like it can't really be done until the robot is mostly assembled and we always do it in place.

One of the ideas I have is to take all of our sensors (limit switches, shaft encoders, pots, etc.) and terminate them to 3 pin female connectors using just a few inches of wire length, which we could do starting week 1 and mount them with the component. Then we would make a cable for each of the sensors, male to female, extra long (or just use pwm extension cables) so we can test out all the sensors. The final task would be to cut them to length, put a new connector on the cut end and secure them along the routing.

Am I headed in the right direction? Is there any problem having an extra connector(s) in every line? Is there any benefit to adding short cables from each input on the controller side to some location with another connector so I can hard mount /strain relieve that termination point as well?

Or any other suggestions?

[Rickertsen2]

Originally Posted by Gary Dillard

This is a follow-on to my thread about 3-pin pwm connectors; I looked through the threads on wiring recommendations and didn't see anything that specifically addressed this....

I am tasked this year with improving the integration of our controls system from a physical hardware standpoint. One of the things that seems to hold us up is cable routing, especially to the sensors. Last year we did a great job cleaning up the power cable routing (love the new relay board), but running small wiring to all the sensors is always the last thing we do. It seems like it can't really be done until the robot is mostly assembled and we always do it in place.

One of the ideas I have is to take all of our sensors (limit switches, shaft encoders, pots, etc.) and terminate them to 3 pin female connectors using just a few inches of wire length, which we could do starting week 1 and mount them with the component. Then we would make a cable for each of the sensors, male to female, extra long (or just use pwm extension cables) so we can test out all the sensors. The final task would be to cut them to length, put a new connector on the cut end and secure them along the routing.

Am I headed in the right direction? Is there any problem having an extra connector(s) in every line? Is there any benefit to adding short cables from each input on the controller side to some location with another connector so I can hard mount /strain relieve that termination point as well?

Or any other suggestions?

I think this is a great idea. I would be sure to use LOCKING 3 pin connectors. The normal 3 pin .1 headers come apart far too easily.

As to the legality, the rules allow you to do pretty much whatever you want with connectors.

[billbo911]

Originally Posted by Gary Dillard

One of the ideas I have is to take all of our sensors (limit switches, shaft encoders, pots, etc.) and terminate them to 3 pin female connectors using just a few inches of wire length, which we could do starting week 1 and mount them with the component. Then we would make a cable for each of the sensors, male to female, extra long (or just use pwm extension cables) so we can test out all the sensors. The final task would be to cut them to length, put a new connector on the cut end and secure them along the routing.

Am I headed in the right direction? Is there any problem having an extra connector(s) in every line? Is there any benefit to adding short cables from each input on the controller side to some location with another connector so I can hard mount /strain relieve that termination point as well?

Or any other suggestions?

Gary, welcome to the wonderful world of compromise.

With every improvement there will almost certainly be a compromise you will have to consider. Having the short "pig tail" on the sensor will allow you to test it with the RC/OI separate from the robot. It will allow you the verify programming prior to actually having the robot completed. Once the robot is assembled, it will allow easier replacement of damaged sensors or cables. All of these are "good". The compromises associated with pig tails include: mechanical instability, in other words, one more place to have to worry about a connector coming apart, electrical instability, the extra connections between wire and pin, and pin to pin will introduce voltage drop and provide another place that that the signal can be degraded. These are just a couple of the compromises. Personally, I think the advantages out weight the dis-advantages.
You can even take a variable approach. In the instances where dis-advantages out weigh the advantages, don't use the extra connectors.

Properly securing these extra connectors will go a long way in making sure you have success!!!

[jgannon]

Originally Posted by Rickertsen2

I think this is a great idea. I would be sure to use LOCKING 3 pin connectors. The normal 3 pin .1 headers come apart far too easily.

Good suggestion. My favorite three-pin connectors are 3.5mm headphone jacks, because they are robust, easy to wire, hard to jiggle loose, and available just about everywhere. I would suggest them instead of the .1" headers to put between your two cables.

[Al Skierkiewicz]

Gary,
Yes you are headed in the right direction. However, remember that wiring stays with the robot no matter what but the sensors and the controller may change if something goes wrong. We add a connector near the sensor with the wiring terminating at the controller. If the sensor is damaged or fails, another sensor with connector attached is pulled from spares. DB9 connectors work very well but are a little bulky. Since you are already wiring the OI inputs through DB connectors, your students have the experience of wiring that style connector and it doesn't require any special tooling. There are crimp ons available from Digikey that are the same as the push on connectors for the fuse panel. They come in both male and female and with a little heatshrink tubing become a perfectly insulated connection, again without extra tooling. Most sensors are either two or three wire devices, and Switchcraft makes a very nice series of connectors that are available with up to 5 pins, have builtin cable clamp, have a metal shell about 1/4" in diameter and have a locking mechanism built in. They are the TA series and are available also from Digikey. (TA3F female TA3M for male) A little on the pricey side ($6/conn) they cannot be damaged and are reusable.