Encoder recommendation for Banebots RS550 ?

[SoloRacr]

Hello all,

I'm brand new to FIRST this year as a Mentor and I'm facing the challenge of encoder and sensor selection.

I've ordered several banebots RS-550-B motors which have a 3/8" encoder backshaft. This will be coupled to a P60 gearbox.
The motor shaft is 3.2mm according to banebots.com

I haven't been able to locate an appropriate encoder that would plug n' play on the back of this motor. Banebots do not seem to offer one.

Is there a US Digital E4 available for this application?
We're beyond crunch-time for ordering parts so I need the expertise of the FIRST community to get this order right the first time. I can't afford to order the wrong part and let the team down.

Any links, p/n's or information would be greatly greatly appreciated. Point me in the right direction and I can do the rest in terms of research, datasheets etc.

Thanks and regards,
Andrew Paul

Team 907, E.Y.C.I Toronto

[Alan Anderson]

Originally Posted by SoloRacr

I've ordered several banebots RS-550-B motors which have a 3/8" encoder backshaft...Is there a US Digital E4 available for this application?

According to the US Digital E4P web page, the largest shaft they accommodate is 1/4 inch.

[billbo911]

As Alan mentioned, the E4P is available in many different bore sizes, .125"(3.2mm) is one of them.
Just make the selection of the part you need and it's options and you will be good to go.

[Joe Ross]

Originally Posted by SoloRacr

I've ordered several banebots RS-550-B motors which have a 3/8" encoder backshaft. This will be coupled to a P60 gearbox.
The motor shaft is 3.2mm according to banebots.com

I haven't been able to locate an appropriate encoder that would plug n' play on the back of this motor. Banebots do not seem to offer one.

Is there a US Digital E4 available for this application?

Any links, p/n's or information would be greatly greatly appreciated. Point me in the right direction and I can do the rest in terms of research, datasheets etc.

There is an E4P with a 1/8 shaft (3.175mm) which might work. Next largest is 5/32.

Originally Posted by Alan Anderson

According to the US Digital E4P web page, the largest shaft they accommodate is 1/4 inch.

The 3.2 mm shaft is extended out the back. The length of the shaft is 3/8".

[SoloRacr]

Thanks Alan & Mr. Bill!

Being in Canada and working through red-tape of school board purchasing departments, ordering direct from US Digital is nearly impossible. So I was hoping that AM or Banebots had this figured out already. They are on our preferred supplier lists.

I think a 3mm collet wheel will do just great.

My risk is that the RS-550 motor doesn't have a compatible mounting pattern on the back of the motor, or (more importantly) that the rear spade connector tabs will clash with the encoder. I need my CAD guys to confirm this. WHY doesn't banebots have a PDF drawing of this motor on their site? gah!

Does anyone have direct experience with integrating an E4P encoder on an RS550 motor?

Thanks again!
Andrew

[Mr. Lim]

Andrew,

Honestly, the thought of direct mounting an encoder to an RS550 has never even crossed my mind. Mostly because I'm still living in the days where processing that many pulses per second was a pipe dream.

I haven't done the math, but you might be close to pushing the limits of the cRIO's FPGA module, which is what handles the pulse counting/timing.

https://decibel.ni.com/content/message/12523

You may want to spec out your pulse per revolutions carefully to make sure everything plays nicely.

On top of that, R49 might limit you if you're planning on mounting the encoder directly to the back of the motor. Mounting holes drilled into the back of the motor likely won't be legal.

[R49]

Motors, servos, and electric solenoids used on the Robot shall not be modified in any way, except as follows:

The mounting brackets and/or output shaft/interface may be modified to facilitate the physical connection of the motor to the Robot and actuated part.
The electrical input leads may be trimmed to length as necessary.
The locking pins on the window motors (PN 262100-3030 and 262100-3040) may be removed.
The connector housings on the window motors (PN 262100-3030 and 262100-3040) may be modified to facilitate lead connections.

To share some experiences, I tend to avoid the E4Ps even though they are really convenient encoders. I've had issues with the disc slipping on the shaft and lose their spacing. Also, don't ever try and disconnect the supplied connectors. It's a quick way to destroy the pads on the PCB. If you choose to use the E4P, be sure to pinch the teeth on the disc so that they provide a death grip on the shaft. I've had a number work themselves loose during a competition.

These days I universally recommend Grayhill 63R series encoders, and to slip surgical tubing over the shaft. Slip the other end of the surgical tubing over the shaft you want to measure. Usually on a shaft that's after the gearbox, as close to the driven assembly as possible.

[SoloRacr]

Thanks for the advice, Mr. Lim

The no-modification rule for motors is an important one.

It was always my intention to adhere/glue the encoder to the motor base using the adhesive transfer option from US Digital.

Shortly thereafter, reality got hold of me and I realized that I was putting the entire functionality of this robot in the hands of double-sided tape.
Fortunately, I've re-thought this strategy and will be monitoring speed using a hall effect sensor.

Another deal breaker for me: We know the RS550 motor to run hot or burn-out if allowed to stall or overheat. The longevity of this motor relies on good air movement. If I were to install a P60 gearbox and a backshaft enocder, I would be blocking all of the vent holes on the motor. Not good.

Thanks again!
Andrew

[billbo911]

Originally Posted by Mr. Lim

..........If you choose to use the E4P, be sure to pinch the teeth on the disc so that they provide a death grip on the shaft. I've had a number work themselves loose during a competition.

These days I universally recommend Grayhill 63R series encoders, and to slip surgical tubing over the shaft. Slip the other end of the surgical tubing over the shaft you want to measure. Usually on a shaft that's after the gearbox, as close to the driven assembly as possible.

I would like to add a bit of advice based on our experience with the E4Ps.
There are "teeth" on both sides of the disk. Long on one side and short on the other. Only pinch the long teeth, not both. If you do both, you end up negating the pinching because the teeth pivot at the plane of the disk.