Motor coupling

Posted by Athena at 1/24/2001 7:40 PM EST

Student on team #481, DART, from De Anza High School.

We are attaching the motor coupling to our motor. There is no hole in the shaft for the screw. Is drilling a hole in the saft a good idea or should we do something else?
thanx ^.^

Posted by Anton Abaya at 1/24/2001 9:35 PM EST

Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.

In Reply to: Motor coupling
Posted by Athena on 1/24/2001 7:40 PM EST:

: We are attaching the motor coupling to our motor. There is no hole in the shaft for the screw. Is drilling a hole in the saft a good idea or should we do something else?
: thanx ^.^

we are also using the same stuff this year and it was my impression that there was no need for a hole in the shaft for the set screw. I could be wrong however becuase our stuff isnt coming till tomorrow.

if the shaft is held in place by the set screw on the motor coupling, then you should be fine… although drilling straight through a shaft works, u usually need not bother when you are dealing with set screws. the only time drilling straight through a shaft would be for pins.

good luck.

-anton

Posted by Andy Baker at 1/25/2001 7:34 AM EST

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

In Reply to: Re: Motor coupling
Posted by Anton Abaya on 1/24/2001 9:35 PM EST:

We just attached the coupling to the gearbox shaft yesterday.

By all means, don’t use a set screw. As Woodie says… “set screws inhale audiably” (suck).

Here’s what we did, and by the way, this operation was made by a machinist, since no coach or student on our team has ever had sucess doing this operation without buggering it up. So, if you want to do this, get a professional’s help.

Put a 3/8" lock washer on the shaft, then thread the motor coupling on (yeah, the one provided by SPI). Screw it on until it bottoms out on the lock washer (lock washer holds it in place).

There is a 1/16" dia. pilot hole on the coupling… use a “spade drill” or a “carbide bit” to drill a pilot hole for a #8-32 screw, all the way through the coupling (this is hard to do).

Once your hole is drilled, use a titanium coated #8-32 tap… I think it’s called “titankote” (or something like that)… to tap all the way through the coupling, with the shaft included. Take your time as you tap… don’t break it or your gearbox is junk.

Then, put a #8-32 socket head cap screw in there, and voila, a killer coupling attachment.

No, the #8-32 screw is not too big, as long as you don’t drill your pilot hole too big.

We used this procedure for the past three years. I think that we’ve only shattered three screws in the gearbox shaft during competition over the years.

Good luck, and be careful… like I said, get a pro to help you with this one!

Andy B.

Posted by Joe Johnson at 1/25/2001 12:32 PM EST

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

In Reply to: No, no, Anton… set screws inhale!
Posted by Andy Baker on 1/25/2001 7:34 AM EST:

Andy,

You folks have been doing this for 3 years?

Why didn’t you share with us?!?

I have a serious question: The 3 failures you have had, what was the fix? Was it a new transmission or just a new screw?

Do Tell.

Joe J.

Posted by Andy Baker at 1/25/2001 12:57 PM EST

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

In Reply to: ONLY 3 FAILURES!
Posted by Joe Johnson on 1/25/2001 12:32 PM EST:

OK, here are some explainations:

Three failures:
'99: TKO’s tank treads had absolutely no slippage. We shredded one gearbox in Chicago. Also, we snapped two pins (screws) during non-important operating times. The gearbox failure was not due to the pin design.

'00: We went through the entire year (including 4 competitions) without any pin (screw) breakages. We just broke one last week, as we were driving TechnoBeast up and down the ramp. I think that the hole was kinda wallered out due to vigorous driving over the course of the year.

The fix was always to simply replace the gearbox and shaft with a new gearbox and shaft. Like I mentioned on a previous post, the switch is not too hard to do, if you have a backup already assembled. We will have backups this year, for sure.

As for sharing, I’m assuming that you’re being sarcastic… we’re given away this design! No, we didn’t exactly tell people how to drill and tap the sensitive hole, but WE weren’t even sure how it was done.

Here’s how I do it:
I brings in 4 gearboxes and couplings to machine shop, and ask friend to pin the coupling to the hardened shaft by drilling and tapping all the way through for a #8-32 screw. They ask “why can’t you do this”… I say “we’ve boogered up 4 gearboxes already, and we’re giving up. I’ll buy you a Dew if you can do it.” About 2 hours later, I find the gearboxes and couplings assembled and lying on my desk.

Like I said, unless you’re a darn good machinist, get a pro to do this for you.

By the way, this is the only part of our machine that we have “pros” make for us. We all have this capability… if other teams want the same, then they should go to a local machine shop and ask them to do this single task.

Your mileage may vary.

Andy B.

Posted by Michael Betts at 1/25/2001 1:15 PM EST

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

In Reply to: Hey, we share!
Posted by Andy Baker on 1/25/2001 12:57 PM EST:

: I brings in 4 gearboxes and couplings to machine shop …] “I’ll buy you a Dew if you can do it.”

Andy,

A Dew? I’d hate to tell you what beverages I have to use as bribes…

Mike

Posted by Eric Reed at 1/25/2001 2:09 PM EST

Coach on team #481, NASA Ames / De Anza High School, from De Anza High School and It could be you!.

In Reply to: Re: Hey, we share!
Posted by Michael Betts on 1/25/2001 1:15 PM EST:

So, is the general consensus that we should NOT use the 1/8" dowel provided by Small Parts? Any teams try this yet?

Eric - 481

Posted by Anton Abaya at 1/25/2001 10:30 PM EST

Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.

In Reply to: So…Dump Small Parts Suggestion?
Posted by Eric Reed on 1/25/2001 2:09 PM EST:

: So, is the general consensus that we should NOT use the 1/8" dowel provided by Small Parts? Any teams try this yet?

: Eric - 481

i guess i need more experience with these set screws…

good info to know considering we were planning to screw the pins and go with the screws (did i confuse u there? ) hehe…

welll, we’ll see what happens…

set screws=bad, pins=good? am i getting it?

-anton

Posted by Anton Abaya at 1/25/2001 10:36 PM EST

Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.

In Reply to: i repeat the “i am a ninny” phrase… :slight_smile:
Posted by Anton Abaya on 1/25/2001 10:30 PM EST:

: : So, is the general consensus that we should NOT use the 1/8" dowel provided by Small Parts? Any teams try this yet?

: : Eric - 481

: i guess i need more experience with these set screws…

: good info to know considering we were planning to screw the pins and go with the screws (did i confuse u there? ) hehe…

: welll, we’ll see what happens…

: set screws=bad, pins=good? am i getting it?

: -anton

well, although machining is half the fun, we’re not that luxurious to have access to one…so we try to manage as much as we can without having to customize stuff and using raw materials that we can fabricate using simple tools.

I guess during heavy torque conditions slippage may happen with the set screws… fine fine… i’ll pin the darn things… (1 or 2? hehe)

-anton

Posted by Brett at 1/25/2001 11:27 PM EST

Student on team #201 from Rochester High School.

In Reply to: i repeat the “i am a ninny” phrase… :slight_smile:
Posted by Anton Abaya on 1/25/2001 10:30 PM EST:

I don’t think the coupler has any set screws… (none that I would consider set screws) It’s threaded and has 4 screws along the side to clamp it down over the drive shaft and whatever you’re driving, as a compression type fitting rather than set screwing.

Posted by Ken Leung at 1/26/2001 12:31 AM EST

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

In Reply to: Re: i repeat the “i am a ninny” phrase… :slight_smile:
Posted by Brett on 1/25/2001 11:27 PM EST:

: I don’t think the coupler has any set screws… (none that I would consider set screws) It’s threaded and has 4 screws along the side to clamp it down over the drive shaft and whatever you’re driving, as a compression type fitting rather than set screwing.

Ok, so the drill motor coupling can be seen as two part: the first half attaching to the output shaft of the drill motor gear assembly, and the second half attaching to a 3/8" shaft. Both halves each have two #6-32 UNC-28 set screws on the side for tightening the whole coulping so it will grip harder on the drill output shaft as well as the 3/8" shaft.

Now the difference between the two halves is that:

the first half (for drill motor gear assembly) is threaded internally so it can be screwed on, with a 1/16" hole on the side for a spring pin to prevent the coupling from unscrewing.

the second half (for a 3/8" shaft) is smooth internally (not threaded), NO 1/16" hole on the side, and a 1/8" keyway so you can make a identical keyway on a 3/8" shaft and use keystock to lock that shaft with the coupling.

Now, what Andy suggested is a modification on the first half, where you use a lock washer to grip the coupling tightly on the motor output shaft (same way lock washers lock nuts on a bolt), and enlarge the 1/16" pin hole, tap the hole, and use a #8-32 screw (which to my knowledge we count that as set screw) instead of a pin to prevent the coupling from unscrewing. Since the lock washer is always locking the coupling pretty hard, there won’t be as much stress on the #8-32 screw, therefore it worked nicely.

As for the other half, I am not sure how strong are the two #6-32 UNC-28 set screw on the side, but on theory they can be tighten so the 3/8" shaft won’t slip out, while the key prevents that 3/8" shaft from spinning freely. But you would want to support both side of that 3/8" shaft anyway because of the side load if you are putting a sprocket on it to drive a drive train. In the process of supporting the shaft on both side and/or mounting a sprocket on the shaft you can figure out a way of making sure that shaft won’t slide out of the motor coupling…

Posted by Anton Abaya at 1/26/2001 12:36 AM EST

Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.

In Reply to: clearing confusion…
Posted by Ken Leung on 1/26/2001 12:31 AM EST:

: : I don’t think the coupler has any set screws… (none that I would consider set screws) It’s threaded and has 4 screws along the side to clamp it down over the drive shaft and whatever you’re driving, as a compression type fitting rather than set screwing.

:
: Ok, so the drill motor coupling can be seen as two part: the first half attaching to the output shaft of the drill motor gear assembly, and the second half attaching to a 3/8" shaft. Both halves each have two #6-32 UNC-28 set screws on the side for tightening the whole coulping so it will grip harder on the drill output shaft as well as the 3/8" shaft.

: Now the difference between the two halves is that:

: the first half (for drill motor gear assembly) is threaded internally so it can be screwed on, with a 1/16" hole on the side for a spring pin to prevent the coupling from unscrewing.

: the second half (for a 3/8" shaft) is smooth internally (not threaded), NO 1/16" hole on the side, and a 1/8" keyway so you can make a identical keyway on a 3/8" shaft and use keystock to lock that shaft with the coupling.

: Now, what Andy suggested is a modification on the first half, where you use a lock washer to grip the coupling tightly on the motor output shaft (same way lock washers lock nuts on a bolt), and enlarge the 1/16" pin hole, tap the hole, and use a #8-32 screw (which to my knowledge we count that as set screw) instead of a pin to prevent the coupling from unscrewing. Since the lock washer is always locking the coupling pretty hard, there won’t be as much stress on the #8-32 screw, therefore it worked nicely.

: As for the other half, I am not sure how strong are the two #6-32 UNC-28 set screw on the side, but on theory they can be tighten so the 3/8" shaft won’t slip out, while the key prevents that 3/8" shaft from spinning freely. But you would want to support both side of that 3/8" shaft anyway because of the side load if you are putting a sprocket on it to drive a drive train. In the process of supporting the shaft on both side and/or mounting a sprocket on the shaft you can figure out a way of making sure that shaft won’t slide out of the motor coupling…

the summary actually helped… :slight_smile:

Posted by Anton Abaya at 1/26/2001 12:39 AM EST

Coach on team #419, Rambots, from UMass Boston / BC High and NONE AT THE MOMENT! :(.

In Reply to: thanks ken…
Posted by Anton Abaya on 1/26/2001 12:36 AM EST:

: : : I don’t think the coupler has any set screws… (none that I would consider set screws) It’s threaded and has 4 screws along the side to clamp it down over the drive shaft and whatever you’re driving, as a compression type fitting rather than set screwing.

: :
: : Ok, so the drill motor coupling can be seen as two part: the first half attaching to the output shaft of the drill motor gear assembly, and the second half attaching to a 3/8" shaft. Both halves each have two #6-32 UNC-28 set screws on the side for tightening the whole coulping so it will grip harder on the drill output shaft as well as the 3/8" shaft.

: : Now the difference between the two halves is that:

: : the first half (for drill motor gear assembly) is threaded internally so it can be screwed on, with a 1/16" hole on the side for a spring pin to prevent the coupling from unscrewing.

: : the second half (for a 3/8" shaft) is smooth internally (not threaded), NO 1/16" hole on the side, and a 1/8" keyway so you can make a identical keyway on a 3/8" shaft and use keystock to lock that shaft with the coupling.

: : Now, what Andy suggested is a modification on the first half, where you use a lock washer to grip the coupling tightly on the motor output shaft (same way lock washers lock nuts on a bolt), and enlarge the 1/16" pin hole, tap the hole, and use a #8-32 screw (which to my knowledge we count that as set screw) instead of a pin to prevent the coupling from unscrewing. Since the lock washer is always locking the coupling pretty hard, there won’t be as much stress on the #8-32 screw, therefore it worked nicely.

: : As for the other half, I am not sure how strong are the two #6-32 UNC-28 set screw on the side, but on theory they can be tighten so the 3/8" shaft won’t slip out, while the key prevents that 3/8" shaft from spinning freely. But you would want to support both side of that 3/8" shaft anyway because of the side load if you are putting a sprocket on it to drive a drive train. In the process of supporting the shaft on both side and/or mounting a sprocket on the shaft you can figure out a way of making sure that shaft won’t slide out of the motor coupling…

:
: the summary actually helped… :slight_smile:

also… as a note, we did everything above except tap hole to fit in a set screw… we figured it did not need it, but if you guys suggest it, i’ll see what our machinist thinks of it…

the shaft end of things is the confusion to us and we are just going to drive on it and just tighten those set screws as much as possible and see what happens. we do not expect to have problems, but we’ll see what happens anyway.

thanks for the info…

-anton
“Set Screws are those babies that make funny noises.”

Posted by Eric Reed at 1/26/2001 5:44 AM EST

Coach on team #481, NASA Ames / De Anza High School, from De Anza High School and It could be you!.

In Reply to: clearing confusion…
Posted by Ken Leung on 1/26/2001 12:31 AM EST:

Actually, Small Parts did not include the 1/16in dowel they had originally listed. They sent 1/8 in dowels instead, with a small “use these instead” note, but no small “install these like this” note. I’m just wondering if the SPI switch to 1/8 in dowels makes this a more attractive method, or if the #8 screw is still the best way. Has anybody actually tried it yet?

Posted by Andy Baker at 1/26/2001 7:17 AM EST

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

In Reply to: clearing confusion…
Posted by Ken Leung on 1/26/2001 12:31 AM EST:

Ooops, I forgot… remove that lock washer after machining. It is there in order for you to clamp on the coupling while not having the shaft turn while making the hole.

Andy B.

ps… also, read my note on set screws!

Posted by Andy Baker at 1/26/2001 7:50 AM EST

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

In Reply to: I forgot: remove the lock washer after machining!
Posted by Andy Baker on 1/26/2001 7:17 AM EST:

Another thing:

Yous guys and your set screws… geesh!

A set screw looks like a small threaded shaft with one end that is kinda pointy and the other end HAS NO HEAD ON IT! The non-pointy end with no head has a socket in the end so that you can turn it with a wrench.

If you see any of these menacing screws lying around your shop, get rid of them!

There are three types of machine screws that some of you may be thinking are “set screws”.

A SOCKET HEAD CAP SCREW is a machine screw with a head on it that has a socket for an allen wrench. This head looks like a stubby cylinder.

A BUTTON HEAD SCREW is a machine screw with a flatter, rounded head on top of a screw. This head also has a socket on it for an allen wrench.

A FLAT HEAD SCREW is a machine screw with a cone-shaped head that fits down into a counter-sunk hole (not counter-bored, that’s a hole for the socket head cap screw). This cone shape also has a socket on it for allen wrenches.

So, now you know the deal. Talking about set screws is like nails on a chalkboard to many of us.

The screws on the side of the SPI gearbox couplings are socket head cap screws… not set screws.

Andy B.

Posted by Ken Leung at 1/25/2001 2:00 PM EST

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

In Reply to: No, no, Anton… set screws inhale!
Posted by Andy Baker on 1/25/2001 7:34 AM EST:

I am wondering why aren’t you guys using key/keyway… I mean, I know both method will work really well, but I tend to think that a key is more reliable than a pin or set screw. I am sure you guys already talked about this, but… What factors contribute to your decision of drilling a hole and put set screw through?

And when you said you’ve been using this for the past three years, I assume you are talking about custom made couplings… or do I not know Small Parts have been providing those couplings for a few years now?

Posted by Andy Baker at 1/26/2001 7:20 AM EST

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

In Reply to: why not a key way?
Posted by Ken Leung on 1/25/2001 2:00 PM EST:

We’ve been pinning the gearbox shaft for three years. It is just hard to do, that’s why we have not directed people to do the same (we wasted many gearboxes trying to do it ourselves).

We are using the keyway for the other end of the coupling.

Andy

Posted by Joe Johnson at 1/26/2001 9:59 AM EST

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

In Reply to: We’ve made a custom shaft, not a coupling
Posted by Andy Baker on 1/26/2001 7:20 AM EST:

We have always managed to use either the double D’s on the motors or the gears that are on the motors already or press on new gears/sprockets or used a trantorque type clamp on coupling.

We have yet to cut a keyway.

Haven’t seen the need as of yet.

FYI.

Joe J.

Posted by Ken Leung at 1/24/2001 10:41 PM EST

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

In Reply to: Motor coupling
Posted by Athena on 1/24/2001 7:40 PM EST:

: We are attaching the motor coupling to our motor. There is no hole in the shaft for the screw. Is drilling a hole in the saft a good idea or should we do something else?
: thanx ^.^

Looking at the graph of the motor coupling, and I assume you are talking about the drill motor coupling, I believe you are talking about the 1/16" hole for the spring roll pin. It is intended to lock the coupling in place by preventing it from unscrewing. So yes, you will need to drill hole in the shaft, and yes, it is safe and a good idea to drill holes on the shaft for mounting this coupling as well as a common way of mounting sprockets on output shafts.

You want to make sure the hole on the shaft to be as small as possible, because the hole will weaken the structure of the shaft according to the size of both the shaft and the hole, and make sure you drill the hole through the center of the shaft. One method of making sure that happens is to use a short countersink bit to start a pilot hole to guide the 1/16" drill bit from sliding randomly on the curvy surface of the shaft.