If set screws suck . . .

Please forgive me, as I’m new to this power transmission stuff. . .

If set screws inhale audibly, what other methods are there of attaching a sprocket to a shaft? Or, in my case, to a timing pulley?

I guess I could just bolt the sprocket right into the side of the timing pulley, but I was curious if there were some other methods that are common?

Here is something i got from a recent Indiana FIRST Workshop that we held last weekend…All this information came from Andy Bakers presentation so maybe he can add/explain even more…

GEAR AND SPROCKET MOUNTING

Shaft to gear or sprocket
-Trantorque (for medium to low loads)
-Collar clamp on a split hub
-Drill and tap through on a hub
-Dutchman’s pin
-Weld
-NEVER use set screws for this

Gear or sprocket to wheel
-Skyway- pin whell to large shaft, or capture spokes w/ a hub
-Using 3-4 holes, attach to wheel, close to perimeter

:slight_smile:

you might want to ask Andy Baker from the TechnoKats. They have wonderful way of doing this.

check the white papers or click onthis design

one thing that you can do it just grind down the shaft to put a flat on it. it will make the set screw hold a lot better

A Woodruff key (a semicircular piece of the end of rod, to fit into the slot cut into the side of your shaft) will do a nice job if you have a milling machine, as will a longitudinal milled slot and a length of square keystock. Both require a key way in the hub of sprockets and gears, which is why so many have them. Another way, is the split hub which pulls the gear / sprocket / pulley onto itself to provide the locking force. :cool:

You could always use Locktite (sp?) :smiley:

Just adding a little about using key way…

It is a nice way if the sprockets don’t have a hub (the section sticking out on the side of the sprocket) on it. It is really easy to do if you have access to milling machine. Just have the machinist mill a slot along the shaft. Then you can easily use a keyway broach set to cut out the key way on the sprocket. So, when you out the sprocket on the shaft, and line up the slots on both of them, they will become a square space where it can fit a square key stock. Of course, you will have to measure out how much you are going to cut away on the shaft and sprocket, but that’s not hard to do.

Drill and tap through is also a good and easy way, if the sprocket has a hub on it. Simply drill through the center of sprocket hub with the shaft inside¡K Then tap it. This is better than using just a pin since the pin will slide out easily.

I am sure no one will recommend doing this¡K but if you HAVE to use a hubless sprocket, and you don’t have access to welding (see below), then you will just have to drill on the side of the sprocket through the teeth (OUCH!), and tap the hole afterward. I am sure there is a rule among engineers against doing this, but so far I haven¡¦t done it and haven’t been warned about doing it…

A Dutchman¡¦s key, if I remember correctly, is simply drilling a hole through the side of the sprocket hub (not through center), and a resulting hole whose center is tangent to the shaft. Then, all you have to do is put a pin through it, and the sprocket will be rotating with the shaft magically! (actually, it¡¦s because the shaft is compressing the little section of the pin against the sprocket¡K I think)

Also, if you have access to welding, then you can weld the sprocket onto the shaft… You will probably need to mill away a chamfer on the sprocket hole for more area for welding…

But if you want the sprocket removable… then you can choose to weld metal pieces perpendicular to the shaft, and bolt the sprocket onto those metal pieces. Circle disks will work as well.

These are some of the easy ways¡K other methods involve cutting the shaft and sprocket hole into different shapes, such as a double D (])¡K

About “locktite”… maybe Lloyd is talking about “tie wrap” or “zip tie” or “cable tie”… Oh yeah, “bar lok” too…

Maybe he meant LOCTITE (gets the spelling from my cool pen i glued together at the Loctite both at the Assembly Technology Expo in Rosemont, Ill.)

:slight_smile:

We have used various methods for attaching sprockets to shafts the last few years. Dowel pins sometimes shear, and are a pain to remove and then reinstall.

If the sprocket will fit on a 1/2" shaft, you can use a 10-32 cap screw instead of the dowel pin. However, this requires a large shaft and sprocket.

Only at our last competition in October did we try set screws with a flat ground on the shaft (10-32 set screw). After wanting to gear the robot down even further, we chose 12 tooth sprockets mounted on 1/4" shafts connected to the drill motors. Our belt walked off the track, locking everything up. The drill motor had enough torque to stretch the chain and move the plate the motors were mounted to, to the point the chain jumped teeth. It eventually bound up, and we smoked our drill motor and toasted a breaker. The set screw never budged which amazed me.

I guess they’re stronger than the dowel pins we’ve sheared, and a whole lot easier than the cap screws (package better too).

Dowel pins inhale not quite so audibly. I would put them one step above set screws on my list of “good ways to attach stuff”, making them second worst.

Welding would probably be my #1, but you had better be sure you have your ducks in a row before you start, or you’ll end up making some wonderful modern art, which isn’t so wonderful when you are trying to build a robot.

Trantorques are nice, but if one slips, you might be headed for a world of hurt. The times I’ve seen them slip, they were being used in a place where the forces were too much for them to handle, and it was back to the drawing board.

When attaching a wheel to a gear or sprocket, I always prefer the method Clark brought up, holes around the perimeter. It’s a very solid method, and I’ve never had a failure there.

Of all the methods mentioned in this thread, the one we probably use most frequently for attaching a hub to a shaft is to drill and tap through the hub and shaft and use a cap screw and nut. We have used 10-32 bolts for 3/8 shafts and it has been ok.

I can’t say we have never had a failure in the form of a sheared bolt, but it is very rare. I suspect that in the case of the few failures, the drilling and tapping were less than perfectly done.

When we have two sprockets next to each other with the same center, we normally bolt through sideways with appropriate spacers. This is very reliable.

Okay. . . here’s what I’ve designed for, so I hope it’ll work -

http://www.magenet.com/~imagination/3dchassis_s.jpg

The motors are driving the wheels via a 3/8" pitch roller chain around a 40 tooth sprocket. That’s the purple disc in the picture.

Toward the outer edge of the 'bot, there’s a 7.132" dia. boreless timing pulley (the green thing) that’s made of cast iron. On the inside are 2" thick polycarbonate wheels that’ll be made of several pieces bolted together.

The shaft is 1/2" dia., but isn’t used to drive the wheels. It exist solely as a surface for the wheels to rotate upon. Since the timing pulley “bore” is 2.188" in diameter, we’ll machine a bearing from Delrin rod to occupy the space between the shaft and the timing pulley.

Instead of driving the shaft, I plan on letting it idle and putting clearance holes through the polycarbonate wheels and sprocket, and tapping 3/4" through the 1" width of the timing pulley. Then, we’ll use 1/4 - 20 threaded rod to tie it all together with appropriate spacing. There are 8 rods around the circumference of the the wheels and sprocket. So, essentially, when the sprocket spins around the shaft, the threaded rod will spin everything else since it’s all attached.

This is my first drivetrain, and it’s practice for us, but we’d love to be able to use this design in January. . . both because it’ll save us a lot of time, and it’s cool :slight_smile:

But, if anyone can see something that’ll surely make this shatter into a million pieces, I’d really appreciate it if you’d share it with me.

Thanks!

If you know you have enough time to make extra parts then I would say weld it but… If not use a keyway and a key. We welded our two gears together and really sucked when half the teeth broke off of one of the gears. We had to sacrafice another transmission off the robot and lose that other transmission’s arm function.

Well, for me, right now, welding isn’t an option.

The timing pulleys are iron, but they’re offset from the sprocket by several inches; and the design wouldn’t work without some serious changes if they were any closer.

The sprocket does butt up against another wheel, but that wheel is to be fabricated from polycarbonate sheet, and thus - no welding.

Give me a few more weeks, and I should know for sure if this all works like it’s supposed to. Otherwise, I guess I’ll just have to redesign a simpler drive mechanism before January.

Taper-lok bushings (ref. Browning Catalog)

I’ve learned a lot over two years :wink:

too bad you werent around a little longer than that
ChiefDelphi Forums > Old Forum Archives > 2001 > What is your favorite method for attaching gears to shafts?

ChiefDelphi Forums > Old Forum Archives > 2001 > Connecting hub sprockets to shafts

:smiley:

I have been :wink: I just never had to do power transmission work until the 2002 season, so I never took the time to learn about it.

We’ve attached gears manny ways in 7 yrs of competition, and the best way so far is by on e of 2 methods, 1) using a hex broach to put a “X” diameter hex in the gear and using a piece of hex stock on the shaft. Keep gear in place with a snap ring. 2) If no broach is a vailable then bore a hole in the gear and weld a “Craftsman” 7/16, 1/2" socket in place and use a apiece of hex on the shaft. Works extremely well and the gear is easily removed and serviced. Also used this “hex coupling” on the output of the trans unit to make it easy to separate the trans from the drivetrain for fast servicing. We could remove the trans in under a minute last season. :cool: