Connecting hub sprockets to shafts

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Posted by Patrick Dingle at 2/2/2001 7:17 PM EST


Other on team #639, Red B^2, from Ithaca High School and Cornell University.



Does anyone know the most reliable way to connect a hub sprocket to a rotating shaft (no keyway)? We are planning to drill and tap the hub, and bolt slightly into the shaft. Is this reliable, or are there better ways?

Thanks
Patrick

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Posted by Ken Leung at 2/2/2001 7:56 PM EST


Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.


In Reply to: Connecting hub sprockets to shafts
Posted by Patrick Dingle on 2/2/2001 7:17 PM EST:



: Does anyone know the most reliable way to connect a hub sprocket to a rotating shaft (no keyway)? We are planning to drill and tap the hub, and bolt slightly into the shaft. Is this reliable, or are there better ways?

: Thanks
: Patrick


I think you probably want to drill all the way, and bolt through the shaft instead of just bolting in slightly. Some where along the line of Andy Baker’s description of attaching shaft coupling onto the drill motor output shaft. This way, you won’t have the risk of snapping the bolt on one side (or screw). And I am pretty sure you won’t have to worry about weakening the structure of the shaft, because the hub sprocket will be fitting around tightly reenforcing it. Just keep the size of the bolt resonable.

Also, when there are laruge amount of force coming from the sprocket, that force will be twisting the bolt on both side, instead of the shaft pushing the bolt outward. It might take a long time to tap the hole through, but I am pretty sure it’s well worth the time.

Or, as another person suggested, you can mill the shaft flat on its side. Just like the shaft of Van door motor and Globe motor, and broach a sprocket with a smaller hole to tight fit around. The flat shape is going to hold the sprocket from free spinning.

Well, other then these, all I can think of is welding the sprocket onto the shaft… and that ALWAYS work.

-Ken Leung

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Posted by Raul at 2/2/2001 9:06 PM EST


Engineer on team #111, Wildstang, from Rolling Meadows & Wheeling HS and Motorola.


In Reply to: Connecting hub sprockets to shafts
Posted by Patrick Dingle on 2/2/2001 7:17 PM EST:



I once considered what I am about to tell you somewhat of a trade secret. Considering that there may be others out there that have used this technique and because I feel bad hearing that so many people are having problems with keying hubs to shafts, I will tell you the best way to "key" a shaft to a hub that does not require a keyway:

It is called a "dutchman" key. You simply drill a hole through the shaft off-center such that it is tangent at the inner interface of the shaft and hub. Then press a dowel pin in the hole.

So why is this so much more reliable than just drilling a hole through the center? Because it is almost impossible to shear the pin. The failure mode is to compress the metal to the point that is has a little freeplay, but it will not break and will not come loose. The hub will crack from the pressure before you will get the pin to disintegrate. But that requires more force than you could possibly produce unless you use a shaft hub that is really small.

BTW, we only use this method on motor shafts or really tight spaces because we have better methods when we can just machine our own shafts. I won't tell you this one right now - just come see our bot at our pits and I will explain.

Raul



: Does anyone know the most reliable way to connect a hub sprocket to a rotating shaft (no keyway)? We are planning to drill and tap the hub, and bolt slightly into the shaft. Is this reliable, or are there better ways?

: Thanks
: Patrick

[archiver]

Posted by Joe Johnson at 2/2/2001 9:51 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: A very reliable method - trade secret?
Posted by Raul on 2/2/2001 9:06 PM EST:



Raul,

Very cool attachment method. I have seen this kind of
joint before, but I have never used them. Being a
careful person, I am lothe to use anything new if I
know some other method that works.

You should have heard me argue against the 4-bar puck
grabber two years back, "Why don't we go with a lift
again? We KNOW how to do lifts. This 4-bar stuff is
all well and good for design classes in college, but
what kind of troubles are we going to cause for
ourselves if we actually try to use it? yada yada yada..."

Anyway, knowing that Raul-the-magnificent considers
them safe territory has put this shaft joining method
on my short list of "approved FIRST practices" Thanks
for the tip.

Now for the topic of the message. I regret ever
having used the term "trade secret" in regard to stuff
that FIRST teams keep to themselves ;-)

I like the term in that it conveys the idea well, but
it seems that it has a negative connotation to most folks.

This was quite a surprise to me because at Delphi, we
use the term all the time in a very positive way. In
fact, Delphi even pays $1000 to employees that submit
Trade Secrets that are accepted by the
intellectual property review board (the same folks that
decide which inventions Delphi should spend the money
to patent).

Anyway, How do other feel about the term? Should we
scrap it?

Joe J.

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Posted by Raul at 2/2/2001 10:20 PM EST


Engineer on team #111, Wildstang, from Rolling Meadows & Wheeling HS and Motorola.


In Reply to: Can I officially take back my "trade secret" comment?
Posted by Joe Johnson on 2/2/2001 9:51 PM EST:



Joe,

I guess I am the opposite. I like to try new techniques every year in some part of the design. BTW, the technique does require a mill with a sturdy cutter to perform; a simple drill press will not work well. But, once the hole is in the hub, we have been successful in using that a a pilot hole in the pits if a motor has to be replaced. We have used this technique on the Van door motor and have never had a failure of the shaft or hub. I suppose it could work on the drill transmission as well. It will certainly hold the new coupling in place much more securely than the screws.

The term "trade secrets" is a perfectly good term and should not be abolished but instead understood. It is a part of the engineering world that all high school students need to appreciate. We, at Motorola, are also taught to respect what we call "intellectual properties", but I like "trade secret" better. In fact, Dean is really sensitizing us to secrets in industry by the recent "IT" (Ginger) publicity. I say keep it and be proud of the hard work you have done in giving yourself an edge. We can all wait until you feel that you have attained new secrets and feel you can divulge your old ones. That is also what is done in industry.

: Raul,

: Very cool attachment method. I have seen this kind of
: joint before, but I have never used them. Being a
: careful person, I am lothe to use anything new if I
: know some other method that works.

: You should have heard me argue against the 4-bar puck
: grabber two years back, "Why don't we go with a lift
: again? We KNOW how to do lifts. This 4-bar stuff is
: all well and good for design classes in college, but
: what kind of troubles are we going to cause for
: ourselves if we actually try to use it? yada yada yada..."

: Anyway, knowing that Raul-the-magnificent considers
: them safe territory has put this shaft joining method
: on my short list of "approved FIRST practices" Thanks
: for the tip.

: Now for the topic of the message. I regret ever
: having used the term "trade secret" in regard to stuff
: that FIRST teams keep to themselves ;-)

: I like the term in that it conveys the idea well, but
: it seems that it has a negative connotation to most folks.

: This was quite a surprise to me because at Delphi, we
: use the term all the time in a very positive way. In
: fact, Delphi even pays $1000 to employees that submit
: Trade Secrets that are accepted by the
: intellectual property review board (the same folks that
: decide which inventions Delphi should spend the money
: to patent).

: Anyway, How do other feel about the term? Should we
: scrap it?

: Joe J.

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Posted by Michael Betts at 2/3/2001 10:18 AM EST


Engineer on team #177, Bobcat Robotics, from South Windsor High School and International Fuel Cells.


In Reply to: Re: "trade secret" comment - don't take it back!
Posted by Raul on 2/2/2001 10:20 PM EST:



Joe,

I agree with Raul. The concept of a trade secret is a good one. Knowing when to "announce" to the world your product's capabilities is critical to a successful project.

Keep the term.

Mike

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Posted by Ken Patton at 2/4/2001 12:17 PM EST


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.


In Reply to: Can I officially take back my "trade secret" comment?
Posted by Joe Johnson on 2/2/2001 9:51 PM EST:




: You should have heard me argue against the 4-bar puck
: grabber two years back, "Why don't we go with a lift
: again? We KNOW how to do lifts. This 4-bar stuff is
: all well and good for design classes in college, but
: what kind of troubles are we going to cause for
: ourselves if we actually try to use it? yada yada : yada..."

Joe, 4-bars are easy, don't be scared of them :)). We did them for our lifts in 1997, 1998, and 1999. You just have to pay attention to the loads where you are driving the linkage. Like you say, simple college engineering. It also helps to counterbalance the mechanism.

Regarding shaft connections, we tend to use the shafts as they exist on the motors, and wire EDM the appropriate shape into the hub of whatever we are driving. We have been using square holes since 1997.

Ken

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Posted by bill whitley at 2/4/2001 8:34 PM EST


Student on team #70, Auto City Bandits, from Powers Catholic High School and Kettering University.


In Reply to: scared of 4-bars, huh?
Posted by Ken Patton on 2/4/2001 12:17 PM EST:



What exactly (or unexactly) is a 4 bar grabber? I (nor anyone else on my team) knows what one is. Times like these I'd kill for an engineer. I don't know what I'm going to do since I couldn't buy Joe J's time with unlimited Dew. Anybody else willing to take that deal? Unlimited dew, or coke or whatever, if you wanna come tell us how many things are wrong with our robot. Its a short drive to Flint. ;-)

Bill
Team 70

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Posted by Dan at 2/5/2001 12:01 AM EST


Other on team - from Carnegie Mellon sponsored by -.


In Reply to: 4 bar?
Posted by bill whitley on 2/4/2001 8:34 PM EST:



"4 bar" is short for "4 bar linkage" which is pretty much just four bars connected by 4 pivots at the corners where one of the bars is static.
If you've ever watched Battlebots and have seen champ Biohazard (the very good and low flipping robot made by a former FIRST coach), it's flipping arm is a four bar linkage. The bars are certain lengths so that the path of the arm goes out and up.
Dan

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Posted by Joe Johnson at 2/5/2001 5:47 AM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: 4 bar?
Posted by Dan on 2/5/2001 12:01 AM EST:



For a long time I was confused by the name 4 bar because I only counted 3 bars! But, in geek speek, the chassis counts as a "bar."

Joe J.

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Posted by Matt Berube at 2/5/2001 9:34 AM EST


Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.


In Reply to: 4 bar?
Posted by bill whitley on 2/4/2001 8:34 PM EST:



Bill,

If you guys ever need help it really is a short drive from Saginaw to Flint. We would be very happy to take a day and come visit you.

Matt B.
T49
The Knights

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Posted by Ken Patton at 2/5/2001 12:34 PM EST


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.


In Reply to: 4 bar?
Posted by bill whitley on 2/4/2001 8:34 PM EST:



One of the great things about 4-bar linkages (or linkages in general, really) is that for their capability, they are relatively simple devices to build and maintain. Couple that with the fact that they are FIRST-rules-friendly (pins in links are free), and they make good FIRST robot devices.

Ken

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Posted by Joe Johnson at 2/5/2001 3:37 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: 4 bar?
Posted by Ken Patton on 2/5/2001 12:34 PM EST:



For all the great things 4-bars can do, I remain a simple pivot kind of guy.

You say, "po-TA-to," I say, "pa-TAA-to."

Joe J.

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Posted by ChrisH at 2/5/2001 1:13 AM EST


Engineer on team #330, Beach 'Bots, from Hope Chapel Academy and NASA JPL, J & F Machine, Raytheon, et al.


In Reply to: A very reliable method - trade secret?
Posted by Raul on 2/2/2001 9:06 PM EST:



: It is called a "dutchman" key. You simply drill a hole through the shaft off-center such that it is tangent at the inner interface of the shaft and hub. Then press a dowel pin in the hole.

Raul,

Thanks for reminding me. I'd forgotten all about dutchman keys. And you're right as long as one half of the joint survives you should be able to use it as a pilot for a replacement of the other half in a field repair.

Chris Husmann, PE
Team 330 the Beach'Bots

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Posted by Ed Sparks at 2/2/2001 10:15 PM EST


Engineer on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.


In Reply to: Connecting hub sprockets to shafts
Posted by Patrick Dingle on 2/2/2001 7:17 PM EST:



Check out those trantorques on page 384 of the small parts catalog. A little costly but very easy to work with. Keep an eye on the "Max Torque" values in the chart and be sure to hold the 0.0015" tolerences on the shaft and bore. I always have our machine shop bore our sprockets/gears on a lathe. You'll see a bunch on team 34's 'bot this year and they are "fasteners" so they don't gig your SP budget. You can buy these a little cheaper from Fenner Drives and even buy an 11mm version that works well on the van door motor shaft.

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Posted by Joe Johnson at 2/2/2001 10:27 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: How about a Trantorque !
Posted by Ed Sparks on 2/2/2001 10:15 PM EST:



Zoinks! Do I feel stupid. I just bought some 10 mm
Trantorques and paid a bit more that what they cost to
have a machinist open them up to 11 mm specifically for
the purposes of using them with the Van Door Motors.

We did this last year and it worked extremely well.

Now that I know where to get 11 mm out of the box, I am
all set.

Thanks.

Joe J.

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Posted by PAUL GIANNOSA at 2/2/2001 11:56 PM EST


Engineer on team #27, TEAM RUSH, from OSMTECH and TEXTRON AUTOMOTIVE CO..


In Reply to: Connecting hub sprockets to shafts
Posted by Patrick Dingle on 2/2/2001 7:17 PM EST:



: Does anyone know the most reliable way to connect a hub sprocket to a rotating shaft (no keyway)? We are planning to drill and tap the hub, and bolt slightly into the shaft. Is this reliable, or are there better ways?

: Thanks
: Patrick
HI PAT. JUST LOOKED @ SOME OF THE RESPONSES TO YOUR POST. I HAVE USED RAUL'S "DUTCHMAN" METHOD VERY SUCESSFULLY ON OUR WHEEL HUBS LAST YEAR AND I AM USING IT ON MY PLANETARY HUB WITCH REPLACES THE FRONT .5 OF THE DRILL MOTOR TRANS. THE DRILL SHAFT IS A CUSTOM ONE TURNED ON A LATHE FROM A GRADE 8 .75 BOLT. WE ARE ATTACHING A 16 TOOTH GEAR TO THE .472 DIA. SHAFT BY USING A DOWEL PIN. THE WAY I DID THAT ON LAST YEAR'S MACHINE WORKED REALLY WELL. WE NVR BROKE A GEAR OR SHAFT. WHAT I DO IS DRILL OUT THE 8/32 THREAD HOLE IN THE HUB TO .187 DIA. I DRILL AND TAP A LARGER 1/4-20 THD HOLE ON CENTER WITH THE .187 BORE. NEXT I BORE A .1875 DIA HOLE INTO THE .472 DIA DRILL SHAFT .200 DP. THIS IS SLIGHTLY LESS THAN HALF OF THE SHAFT. I CUT A .187 DOWEL TO FIT INTO THE GEAR AND SHAFT AND HOLD IT IN PLACE WITH THE 1/4-20 SET SCREW. I DON'T THINK YOU COULD GENERATE ENOUGH FORCE TO SHEAR A DOWEL PIN THAT IS ABOUT 45-55 ROCKWELL C. YOU ALSO MAINTIAN STRENGH IN THE SHAFT BY NOT BORING A HOLE COMPLETLY THROUGH. SORRY IF I'M A LITTLE WORDY. I CAN SEND YOU A AUTOCAD14 FILE SHOWING YOU GRAPHICALLY HOW I DO THIS. MY E-MAIL IS PMGRACER@AOL.COM

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Posted by Joe Johnson at 2/3/2001 4:58 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: Connecting hub sprockets to shafts
Posted by PAUL GIANNOSA on 2/2/2001 11:56 PM EST:



Paul,

I am very interested in your design. Can you make a
jpeg of your AutoCAD screen as well as snap a digital
photo of your actual modifications?

I would love for you to upload some files to our Photo
Gallery. The upload feature allows you to put in some
explanatory text.

We would love to see it.

Of course a White Paper would be even better.

What do you say?

Joe J.

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Posted by PAUL GIANNOSA at 2/4/2001 11:25 PM EST


Engineer on team #27, TEAM RUSH, from OSMTECH and TEXTRON AUTOMOTIVE CO..


In Reply to: upload a Jpeg to the Misc Photo Gallery.
Posted by Joe Johnson on 2/3/2001 4:58 PM EST:



: Paul,

: I am very interested in your design. Can you make a
: jpeg of your AutoCAD screen as well as snap a digital
: photo of your actual modifications?

: I would love for you to upload some files to our Photo
: Gallery. The upload feature allows you to put in some
: explanatory text.

: We would love to see it.

: Of course a White Paper would be even better.

: What do you say?

: Joe J.
HEY JOE J. I'M GLAD SOMEONE READS THIS STUFF. I CAN EMAIL YOU A AUTOCAD14 DRAWING/ BMP OR WHATEVER DATA YOU WANT. IT WOULD BE BEST IF YOU COULD GIVE ME A CALL TO MAKE ARAIGMENTS. MY PAGER # IS 810-418-1035. PAGER IS BEST. MY EMAIL ADDERSS AT HOME IS PMGRACER @ AOL.COM AND MY WORK MAIL IS PMG6 @DCX.COM. I JUST FINISHED WORK ON THIS YEARS MOTOR MOUNT SYSTEM. I GOT RID OF THE FRONT HALF OF THE TRANS, USING ONLY THE PLANETARY RING AND GEARS AND BUSHING, AND MAKNG A NEW "HUB SHELL" SO THAT YOU CAN MOUNT THE MOTOR SYSTEM OFF OF THE FRONT OF THE SHELL. THE TRANS BOLTS TO THE SHELL AND THE MOTOR IS CLAMPED TO THE SHELL. IT IS ALL ONE UNIT. I DID NOT USE THE PIN SET UP TO LOCK THE GEAR ON THE .472 SHAFT BEING WE ARE USING A 16 TOOTH HUBBED GEAR. THERE IS NOT ENOUGH MEAT TO USE A PIN. SO I MILLED A SLOT .125 DEEP IN THE SHAFT AND USED A .156 DIA END MILL TO PUT A .03 DEEP RADIUS IN THE GEAR. THIS WORKS LIKE A KEYWAY WITH A TWIST. I USED A .156 DOWEL PIN WHICH WILL NOT SHEAR. I STILL PREFER TO PUT THE PIN PERPENDICLUR TO SHAFT, BUT DESIGN WON'T ALWAYS COOPERATE. HOW IS YOUR ROBOT PROGRESSING? WE DROVE OURS UNDER ITS OWN POWER SAT @ 3:30PM. STILL ALOT OF STUFF TO FINISH THOUGH!!! TALK TO YOU SOON, PMGRACER