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#1
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Connecting hub sprockets to shafts
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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#2
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all the way through
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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#3
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A very reliable method - trade secret?
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 |
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#4
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Can I officially take back my "trade secret" comment?
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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#5
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Re: "trade secret" comment - don't take it back!
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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#6
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Re: "trade secret" comment - don't take it back!
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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#7
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scared of 4-bars, huh?
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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#8
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4 bar?
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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#9
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Re: 4 bar?
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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#10
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and the 4th bar is the chassis...
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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#11
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A short drive.
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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#12
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Re: 4 bar?
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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#13
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I am still a simple pivot kind of guy...
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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#14
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Re: A very reliable method - trade secret?
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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#15
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How about a Trantorque !
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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