POT round or flatted shaft?

I do not understand the preference for a 180 POT with either a round or flatted shaft for use with the 12v DC worm gear motors.
From searches, people have used both over the years and never mentioned flat or round.

I'm curious as to if there is even a reason for one over the other in this case. Putting together the list and buying parts, so would like to make informed choices.

Tried searching "2620657 round" and "2620661 flatted" with no quotes. Maybe a flatted gives an implementation benefit, maybe round does, or maybe it doesn't matter They cost the same and since I'm ignorant and curious, have got to ask

Round:
https://www.digikey.com/product-detail/en/6127V1A180L.5/987-1387-ND/2620657

Flatted:
https://www.digikey.com/product-detail/en/tt-electronics-bi/6127V1A180L.5FS/987-1392-ND/2620661

Thanks, checked out the FAQ for how to connect / protect a pot
and it helped me understand that since I'm getting:

6127V1A180L.5
and the 6127 datasheet
lists the shaft at 1/4" (6.35mm)

That as long as my chosen flexible coupling has range that includes 6.35mm, it'll work with the POT, like the ones linked in the FAQ have 6.35mm-12mm range, and some at amazon have 5mm-8mm range. Having one that starts at 6.35mm may fit nice and snug at the outset.

Thanks, kind of thinking out loud as a log of learning on the way to buy/build. And of course, in case my understanding is wrong!

Just to mix things up but there are Hall sensors that allow total non-contact angle sensing for feedback. They are just like the ones with shafts but instead of connecting to a shaft and having to allow for small misalignments in the motion, you mount the magnet on the motor output shaft and mount the sensor itself in the right location relative to the magnet position. The ones I used allow for a couple of mm misalignment and that’s easy. No friction, binding, or flexible couplings.

@Zed thanks, I didn't mention it anywhere, and am glad you brought up Hall sensors, as I've only refereed to "POT." The intention is to definitely get Hall sensors or Hall sensor POTs as recommended in many threads (and as you just described), I neglected to mention it in any of the posts in this thread. I went with this POT for what you just said, - to have a non contact "Hall sensor POT." The detailed description for the product states, "Hall Effect Sensor Rotary Position Round Shaft Solder Turret." From what I understand from the linked PDF above, the 6127V1A180L.5 is this kind of "Hall Sensor POT" and can help achieve what you are speaking of?

I've read posts abut people buying separate Hall sensors and going DIY, but thought that was a "Hall Sensor POT," and therefore sufficient. Your implementation of "non contact" sounds like the ideal recommendation, and would appreciate it if you could checkout the item link/pdf and verify that the linked 6127 is the right item, or if I need some extra components.

I could be ready to buy the completely wrong item, as am just going through threads getting a laymen understanding of the components, even though I don't understand their functions yet. Thanks again!

EDIT: I did go this build page and check it out:
https://www.xsimulator.net/communit...-build-a-3d-printer-has-been-essential.10642/

@gSeat - that pot isn’t what I was meaning by non-contact. I think what they mean is there is no electrical contact as there is in a wire wound or thin film potentiometer. The 6127 has an input shaft that still has to be aligned properly with what drives it or use a flexible coupling of some kind.

These are what I used: https://www.digikey.com/product-det...ity-solutions/RTP180LVEAA/480-6128-ND/5252730

These are totally non-contact in every sense and they work perfectly with the JRK 12v12. You mount the magnet on the rotating part and the body in the proper position. I used mounts that tied the bodies to the motors so any motor mount flexing wouldn’t affect the Hall sensors since the Hall sensor moves with the motor. But the magnet does not touch the sensor body when properly set up. No bearing, no friction, no wear, no maintenance. Cost for these is more expensive than some Hall sensors (at $42 each) and cheaper than others. You also need the mating connectors for these. Others have wires and terminals, or even need a circuit board. DigiKey has 5 pages of truly non-contact Hall sensors to choose from. But shafted versions are fine too. You just need to be careful about alignment and allowing for minor misalignment.

But it’s not really correct to refer to Hall sensors as potentiometers. Two different effects that produce the same output signals only under certain circumstances. As luck would have it, the way you connect a pot to a JRK and Hall sensor I linked produce the same outputs.

These are a bit hard to make things out since I printed the plastic in black and it doesn’t photograph well, but it should get you the idea. The black thing in the center of the output shaft is the magnet. It has a couple of setscrews that lock it in place on a little adapter I printed that fits snug inside the hollow output shaft.

In the second photo you can see the end of the 1/4" mounting stud on the lower left and the printed plastic adapter on the lower right mounting. In the third photo the sensor mounting plate and sensor is mounted up.

That’s how I did it but there are as many ways as people. And again, shafted sensors work great too.

@Zed Amazing info and description - and thank you for the pics. The whole, "No friction, binding, or flexible couplings, maintenance" is definitely enticing at around an only $20 increase cost per motor. I'll have to stew on this over the weekend and read around some more, as I see some forum matches for "RTP180LVEAA."

Did you design the printed parts yourself?

I did. I was going to post it all when I put up my build thread but I’m happy to post the stl files now if you want to print.

The mounting plates have internal pockets to set nuts into during printing. The standoffs are internally threaded 1/4-20 since that was the stud size I used to mount my motors. I also have a long standoff for the top because at first I didn’t have a bolt on that one but was getting some flex so added a plate and a bolt. But you either print three of the short standoff’s and three nuts or two shorts and a long and 4 nuts. Or just use regular bolts and nuts. The plates are the critical part and the application note shows the proper gap which the standoff’s get you with a thin washer in there.

One thing about the standoff’s is you want to chase the threads with taps and dies to keep stresses low. In all the disassembly/reassembly steps I’ve had to print extras since the threads would sometimes break.

But there are also mating connectors required ($1.50 each plus you need the contacts). Those connectors are latching and make disassembly and reassembly trivial. So these do take more work but to me it was worth it. They make for a very neat installation but you need to be comfortable with tiny crimp connectors or willing to just solder to the sensor pins.

If you do a search at DigiKey, there are also sensors from Littlefuse that look good and are also non contact. They are cheaper, have wire leads, and would need a different mounting. I haven’t used them to say for certain that they are interchangeable, so make sure they are appropriate. I think they are something like $12-15 so not as big a deal if there are issues. They are cheaper but you would need to engineer proper mounting to get the proper alignment. Even without a bearing, alignment is important or it can make the response go a bit non-linear. A motion platform is probably pretty forgiving though.

@mirkobastianini used these on his platform so his opinion may be helpful to see what he thought.

I’ll go ahead and post the files and you can use them or not as you wish.

Here are the .stl files. The units on the standoffs and nut are in inches and the plate is in mm.

@Zed man, thank you so much, incredible...I'm conflicted about which way to go just because it's my first time around, and of course just want to "get up and running" but the contact/maintenance free seems ideal, thanks for mentioning @mirkobastianini I'll contact him to ask about perceived implementation difficulties vs regular pot/hall sensor

Appreciate all of this info, and others that come across this will as well
maybe @Pit can add this to the POT FAQ where it talks about how to configure them, it seems like such a great alternative to the norm. Thank you a ton!
NOTE: only reason conflicted really is that I don't posses a 3d printer - and this seems like the final thing pushing me to getting one, and it may be...

Man, only one tip. Don't have fear (if you can) to spend little bit of money on this things regarding simulator. This kind of potentiometer is the best you can use, is no-contact, so there a no mechanical fault possibilities.
And it's compact and beautiful.

Best choice.

getting a 3d printer by Monday some time... I'm eyeballing the one that includes the @Zed and @mirkobastianini tech support line since they went this route Kidding...diving deep into the rabbit hole with a smile

So much of this was new and intimidating when I started. I didn’t know anything about 3D printers or motion platforms - and there is a lot to know. But taken in little bites it’s not bad at all.

Getting ready to order
The non contact 480-6128-ND
https://www.digikey.com/product-det...ity-solutions/RTP180LVEAA/480-6128-ND/5252730
and
282087-1 connector
https://www.digikey.com/product-detail/en/te-connectivity-amp-connectors/282087-1/A105021-ND/1860707

If there is anything else from digikey I ought to pick up with this order, I'd appreciate a heads up - I got 3 JRKS from Pololu, and will get extra wiring maybe heat shrink too form amz/other. Cheers, happy weekend!

@gSeat - those connectors are just the bodies. You also need the connector sockets that are for the AWG wire you are using. Also, note you need to extend (not pull out completely) the little red strip to be able to set the connector sockets in place. It locks them in place when you push it back in. But it also locks them out if it is pushed in when you are trying to set them in. Be sure to see the data sheet. The sockets are cheap. I’d get some extra just to be safe if you haven’t manually crimped connectors before.

And also, if you aren’t comfortable with the added complexity, there are other more conventional Hall sensors that cost less. But you do need to mechanically couple them.

Those look nice, thanks - Do people use the larger terminal blocks even if using thinner wire for ease of working with the JRKs? The connector sockets are for "CONN SOCKET 15-18AWG" so they can't (at least the specs say) work with thicker wire - but those connector blocks look like they'd make working with the jrks just a bit easier?

@Zed thank you for mentioning the connector sockets (I was unaware of them) oddly, at least to me, - found them at
https://www.digikey.com/en/product-highlight/t/te-connectivity-amp/amp-superseal-ip67-connectors
by clicking on the link for "Featured Product AMP SUPERSEAL IP67 Connectors " - on the 282087-1 web page. Maybe you and @mirkobastianini have some input regarding those large terminal blocks as well - like did you use those terminal blocks and end up using thicker gauge fine with the connector sockets?

Regarding the complexity - yup will be fun adapting to it and learning - you and @mirkobastianini sold me on these,- plus these are tried and true by the both of you so just rolling with them instead of trying to save a few bucks and risk something that doesn't work or I can't figure out in a timely manner BUT thank you for describing where to find the cheaper alternatives!

The wiring for the Hall sensors doesn’t need to be heavy gauge. It’s just milliamperes on those wires. You only need enough gauge really for strength and durability. You should twist the wires, though. It helps to minimize noise pickup.

This picture shows the twist but also shows a bit bulkier, older, mounting plate than the .stl files I posted. The new plate is clearanced to give more room for the system to sag and still not have output arm fittings hit the plate - at least on my system.



On those big terminal blocks for the JRK, they are a good idea if you aren’t just going to solder to the board. You do want the ability to disconnect, though. I used bullet connectors on pigtails I soldered directly to the boards.

These don’t show the actual connections on the JRKs, but you see the bullet connectors. I forgot to take photos of the JRK connections. They are upside down in the square red housings with the heat sink/fans. You need to be a little careful with the screw terminals because if you overtighten them, you can strip them - what I did but with the stock ones - and had to take them back off the boards. The larger ones should be harder to strip but that’s why I went to soldering direct and using the bullets.



But if you are going with screw terminals on the JRKs, I’m definitely with @noorbeast. It sounds like you are considering just using thinner wire gauge overall but something to keep in mind is there are voltage drops. You can look up typical wire resistances by gauge online per unit length. Get the length of your runs and that gives you the wire resistance. Voltage drop is just i x R so is proportional to the amount of current you are pulling and 30 or more amps is quite a bit. Lost voltage is lost current and torque and turns to heating in the wires. The pgsaw motors have fairly small gauge wire leads. I cut mine back to just a couple of inches and put bullet connectors on them. The rest of my wiring is all 10 AWG to minimize resistance losses but I also have other stuff in the circuit so wanted to minimize losses.

Can’t tell you how necessary the heavy gauge is. It depends on how long your runs are. https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table At 4 feet (remember it’s total length both ways), the resistance of 14 AWG is 0.01 ohms. At 30 amps that’s 1/3 of a volt lost and turns 12 volts into 11.7. It’s not huge but if your wire runs are longer, it can get significant. And all other resistances in the loop count too - connectors, circuit boards, motor leads, etc. Just something to be aware of. 12 gauge should be fine for reasonable runs. Maybe even 14 for short runs.

Last photo shows the Hall wiring. Black is ground, red is +5, yellow is feedback/signal.

In my opinion, to do a good job, you need to recreate the possibility to disconnect all...so you really need those large connector for JRK and use 10 AWG cables to avoid overheating.