Help! Direct Drive Issues

[roberthan]

Hi
I'm wondering what's the most direct and easiest way to link an older drill motor with a wheel (any size that's provided in the recent kits)

I'm not really an expert in drive-train, so please excuse of my newbie-ish question. Any suggestions regarding to direct drive or drill motors will be greatly appreciated

-thanks in advance

[sanddrag]

Can you tell us a bit more about exactly what you are trying to do? Thanks.

[roberthan]

I'm trying to build a similar device as the commonly seen ball shooter system from 2006. With the two wheels spinning in different directions, in order to launch a tennis ball.

I'm not really building this as part of my robotics team, but I do plan to borrow some parts from my robotics team. Therefore, I'm trying to keep the design as simple as possible and use the least amount of parts.

[sanddrag]

Are you trying to link just the drill motor itself to the wheel or the drill motor and gearbox to the wheel? What model drill? Do you have a certain diameter wheel in mind? After we have these couple more bits of information, I think I'll be able to start helping you get this figured out.

[roberthan]

I'm going to try to link the drill motor with a gear box to a wheel, I'm not sure exactly which wheels I will use since this contraption is still in the planning stages. (I still have to find out which wheels they have available, maybe the 6 inch wheelchair wheel or the older 9 inch skywheel? those that came in 2002 or 2003 kits) In general, is direct driving with drill motor something that can be easily done or it might take some effort?

I will try to get back to you as soon as I can on the wheels.
thanks for all the troubles.

[SamC]

I think he is trying to make a launcher/shooter similar to these

[sanddrag]

Alright. Well, let's say a drill motor and gearbox in high gear gives us a speed of about 1200 RPM. With a 6" wheel, this equates to a linear speed of about 21 miles per hour at the surface of the wheel (I can go into details on that if you'd like) which is good for a range of about 29 feet if shot at a 45 degree angle (assuming the ball actually leaves the "muzzle" at 21mph and there is no air resistance) Excellent projectile motion calculator/explanation

So, if about 25 feet is an acceptable range, it seems like a 6" wheel spinning at about 1200 rpm would be the hot ticket (and is approximately what a drill motor output would be). If you want to fly farther, up the size of the wheel or the speed of the motor

So, now on the the question, coupling and mounting.

If you have space to put it in line, you can do a direct couple by means of flex coupling. Search www.mcmaster.com for flex coupling. What you do is mount the wheel to an axle such that the wheel is rotationally locked to the axle. Have a couple pillow block bearings (sold at good hardware stores and included in the KOP a few years back, otherwise seach www.mcmaster.com for pillow block) on either the axle on each side of the wheel. Then mount the drill. Then you use the flex coupling to attach the axle to the drill gearbox output. This presents a problem however. Most drill gearbox outputs are threaded (usually 3/8-16 or 1/2-20). Unforunately, most flex couplings are not. So you'll either need to tap it (cut internal threads, with a tool called a tap) or use the stock drill chuck and put a the flex coupling on a shaft that goes into the drill chuck. You either need to make sure the drill rotates in the direction that would tighten the coupling or you need to use a left hand screw anbd washer into the end of the drill gearbox output shaft (all drills have this. if you open a drill chuck as wide as it will go and shine a flashlight in there you'll see a screw head. this is a reverse thread screw that keeps the chuck on)

Instead of a flex coupling, you could install a sprocket onto the drill geabrox output shaft and onto the wheel or axle so you wouldn't have to have the motor inline with the axle. Use a chain to link them. You can either attach a sprocket to the wheel and have bearings in the wheel and a dead (fixed) axle, or you can attach the sprocket to the axle and have the wheel attached to the axle (like the above flex coupling method) with something like a keyway). The spoked Skyway wheels have provisions for bearings and are meant to run on a dead axle and have the sprocket drive the wheel directly. The Skyway Beadlok wheels usually have a keyway and are meant to have a keyed sprocket on a keyed axle to drive them.

To mount the motor, hose clamps (available at any auto store or in the plumbing section of your hardware store) would be a good place to start. It is also possible you could carve some mounts out of wood. Depending on the size and geometery of the motor and gearbox, U bolts might do the trick. Be careful to not take the motor out of alignment with the gearbox in your mounting setup.

If you are looking to do a two wheel setup like the above picture, you'll need them to spin opposite directions otherwise the ball won't be going anywhere. You can do this with gears, some really fancy chain routing (complicated, idler sprockets needed), or two independent motors (like the picture above). Two motors would probably be the best choice so you can control the spin on the ball by varying the speed of the motors.

Also, remember to factor in a bit of "squeeze" on the ball when designing your mechanism. For a tennis ball I imagine it wouldn't be much. It takes trial and error to dial it in.

I hope this helps. Let me know if you have any questions on anything.

[Alex.Norton]

actually the squeeze on the ball can be a very important factor. You can get the ball moving faster than the actual spin of the wheels because the ball will push itself out of the wheels. This year we actually looked at a tennis ball pinching machine and the wheels squeezed the ball and extremely large amount. Like an inch or an inch and a half if I remember.

just a thought

[yongkimleng]

In addition, if you're using two seperate motors you'll probably want to include encoders and use PID to keep both motors in constant rpm.

An interesting thing here is that if both wheels are spinning at different rpms, you can actually control the X direction to a certain extent!

[Dick Linn]

You might want to consider putting a drill chuck on the drill and fastening that to your drive axle. Harbor Freight has various types from $5 to $10. Just search on "chuck". Homier.com has a complete 12v cordless drill for $10! Item 02899.

[Mr. Lim]

Originally Posted by yongkimleng

In addition, if you're using two seperate motors you'll probably want to include encoders and use PID to keep both motors in constant rpm.

An interesting thing here is that if both wheels are spinning at different rpms, you can actually control the X direction to a certain extent!

it's no wonder the robots pictured above (2006 Niagara FIRST Triplets) were codenamed "Beckham" during development.

[yongkimleng]

Originally Posted by SlimBoJones

it's no wonder the robots pictured above (2006 Niagara FIRST Triplets) were codenamed "Beckham" during development.

Lol I'm sorry? Didn't quite get you..

[Tom Bottiglieri]

Originally Posted by yongkimleng

Lol I'm sorry? Didn't quite get you..

David Beckham is a soccer player from England known for his ability to "bend" the path of the ball when he kicks it. Running the motors at different speeds puts lateral spin on the ball and causes the same effect. Hence, the code name.

[yongkimleng]

Originally Posted by Tom Bottiglieri

David Beckham is a soccer player from England known for his ability to "bend" the path of the ball when he kicks it. Running the motors at different speeds puts lateral spin on the ball and causes the same effect. Hence, the code name.

Oh haha no wonder.. I ain't a soccer fan! Well yes thats precisely the theoretical idea I had in mind.. wether it really works with that setup is another thing.

[Mr. Lim]

Originally Posted by yongkimleng

Oh haha no wonder.. I ain't a soccer fan! Well yes thats precisely the theoretical idea I had in mind.. wether it really works with that setup is another thing.

They never did it in competition, but those drill gearboxes pictured above (2006 Triplets) are multi-speed. I remember having a discussion with a member of NiagaraFIRST about running each side in a different gear, and getting a repeatable amount of curve. I'm pretty sure they were quite successful during testing.

But as most FIRST teams found out when it came time to actually win games: why shoot crooked when you could shoot straight?