Building a robot for a class project! Driveline question

[flamewulfe]

So, I'm building a 'bot for a class project, and have a question:

What's the best way to secure a lawnmower style wheel (simple plastic hub) to a 7/16" threaded shaft? I found a killer deal on Amazon for these seat motors (http://www.amazon.com/gp/aw/d/B005IR1NBA/ref=redir_mdp_mobile), which look like they are torquey enough to propel a decent amount of weight (10 - 15lbs) at a slow to moderate speed.

I can't come up with a fairly easy but secure way to lock the wheels onto the threaded shafts of the gear motors; the thread is nonstandard, so no hope of threading things directly on.

Any ideas?

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[Buickguy]

drill a hole thru the shaft and drop a roll pin in it and use washers and a nut to secure the wheel on.

 

[racingtadpole]

drill a hole thru the shaft and drop a roll pin in it and use washers and a nut to secure the wheel on.

If you also file two half round slots in the back side of the wheel hub that match the roll pin, it will be keyed onto the shaft.

 

[theoldwizard1]

Buickguy is sending you in the right direction. Actually, if you read the Amazon page with a "real" computer you would have seen

Threaded shaft is at a right angle and is 4-1/8" x 7/16". Shaft thread is non-standard, so treat it as a smooth shaft and mount pulley or gear with a setscrew.

The set screw would go through the wheel hub and clamp on to the threaded shaft. I don't know how well the would hold up because the hub is probably plastic. A roll pin, at least the length of the outer diameter of the hub going all the way through the hub and shaft, would hold up better.

If the ID of the wheel hub does not fit snugly to the axle (threads), clean the threads and wheel bore with alcohol and fill the gaps with epoxy. You will still need the roll pin in order to get positive engagement from the axle to the wheel.

 

[flamewulfe]

Hey guys, thanks so much for the ideas! You think it will be possible to drill these guys for a roll-pin (http://www.harborfreight.com/materi...free-tires/7-inch-semi-solid-wheel-98951.html)?

Can't find the size of the bore of these online. Guess I'll find out when I pick them up.

Think a hub sleeve or spacer could be used if the bore is bigger then 7/16"?

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[flamewulfe]

Oh wow, this looks slick (but expensive!):

http://forums.parallax.com/showthre...ar-Wheel-and-Motor-Mounts-Feedback-Requested!

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[theoldwizard1]

Hey guys, thanks so much for the ideas! You think it will be possible to drill these guys for a roll-pin (http://www.harborfreight.com/materi...free-tires/7-inch-semi-solid-wheel-98951.html)?

Can't find the size of the bore of these online. Guess I'll find out when I pick them up.

The hub does not stick out very far so there will not be enough clearance for the drill chuck to make a straight hole using a standard length 1/8" drill. They do make extra long drill bits but they are hard to find.

Think a hub sleeve or spacer could be used if the bore is bigger then 7/16"?

1. 5 minute epoxy is your friend. Just remember it take several hours to fully cure rock hard. Also clean both surfaces with alcohol before using epoxy.
2. Work with gravity not against it.

If you are going to fill the gap between that threaded drive axle and the ID of that hub, you can use epoxy. It will run out unless you punch a hole in a small piece of light cardboard (business card or poster board) and put the axle through it (with a piece of wax paper in between so the epoxy won't stick to the cardboard) flush up to the axle hub. Remember rule #2.

The epoxy will not be strong enough to hold the wheel to the shaft when the motor is operating. You still need a way to pin the hub of the wheel to the shaft.

 

[mds5951]

what about turning it down and rethreading it?

 

[mds5951]

Or what about cutting the shaft and welding a bolt/all thread on? You'd have to take your time and make sure not to warp it by welding and make sure it's dead center

 

[flamewulfe]

Still haven't gotten the wheels yet, but I ran into another problem I may have already solved; after looking at the tentative design, I realize I should probably use some sort of bearing/pillow block to help support some weight, between the wheel and the motor. I couldn't find any with a 7/16" bore (is a shaft that size unheard of?), so what I did was order 5/8" bore pillow blocks with 7/16" to 5/8" reducer sleeves, all found on Amazon. Pricey for what they are, but I think they'll work.

 

[flamewulfe]

what about turning it down and rethreading it?

I don't have access to a lathe, easily. But didn't think of that.

 

[flamewulfe]

Or what about cutting the shaft and welding a bolt/all thread on? You'd have to take your time and make sure not to warp it by welding and make sure it's dead center

I can weld, but I'm not sure I'm good enough to align them perfectly. Is this something typically done with some sort of homemade jig?

 

[theoldwizard1]

So how heavy is this thing going to be ? Those pillow blocks look like overkill, depending on how much this thing has to carry.

P.S. Don't forget tp shop eBay !

 

[theoldwizard1]

Or what about cutting the shaft and welding a bolt/all thread on? You'd have to take your time and make sure not to warp it by welding and make sure it's dead center

I can weld, but I'm not sure I'm good enough to align them perfectly. Is this something typically done with some sort of homemade jig?

A jig required in order to get the new axle dead center. Also kind of risky because the gears in side the housing are likely nylon/plastic and the heat might melt them.

Another thought. Get a piece of steel tubing that is 7/16" ID and 5/8" OD. Cut it just shorter than the length of threaded section. Tack weld it to the shaft at each end. Now you can thread the outside with with standard threads. Use standard nuts and external star washer to drive the wheel !

Use jam nuts to lock the nuts.

 

[srmofo]

What's The Duty Cycle On Those Motors? In My Limited Experience With Seat Motors They Tend To Over Heat Quickly. If You Are Planning On Using Them As Drive Motors I Think You Are Going To Run Into Problems If You Plan On Driving It More Than A Few Minutes Without Cool Down time

 

[flamewulfe]

So how heavy is this thing going to be ? Those pillow blocks look like overkill, depending on how much this thing has to carry.

P.S. Don't forget tp shop eBay !

Well, it's basically a Shop Vac version of a Roomba. I ordered a small 12V car shop vac to start with, just to finish the project for the class, but I'd eventually like to upgrade to a larger duty Shop Vac, using the same hardware. I'd like to keep as much of the original hardware as possible, hence the beefiness of the driveline. How cool would this be to clean up all the sawdust/metal shavings between projects?!?!

A jig required in order to get the new axle dead center. Also kind of risky because the gears in side the housing are likely nylon/plastic and the heat might melt them.

Another thought. Get a piece of steel tubing that is 7/16" ID and 5/8" OD. Cut it just shorter than the length of threaded section. Tack weld it to the shaft at each end. Now you can thread the outside with with standard threads. Use standard nuts and external star washer to drive the wheel !

Use jam nuts to lock the nuts.

You know, I didn't think about sleeving the entire shaft; I bought short 1" sleeves to make the added bearing blocks work. How well do you think the 'sleeving' would take threads? Dependent on material type?

What's The Duty Cycle On Those Motors? In My Limited Experience With Seat Motors They Tend To Over Heat Quickly. If You Are Planning On Using Them As Drive Motors I Think You Are Going To Run Into Problems If You Plan On Driving It More Than A Few Minutes Without Cool Down time

Nuts. I didn't think of that. I guess I'll hook them directly up to 12V DC, and monitor them for a while with the temp gun. Do you think they'll heat up without a load, or do they need to be loaded to really get an idea of how they hold up?

I started writing some of the drive code already for the 'bot, but I'm waiting for some more of the hardware to come in before I hit the construction hard and heavy. I'm using ultrasonics for distance (may flip to IR sensors if the ultrasonics are too noisy), and the microcontroller platform I'm using is the BeagleBone Black: http://beagleboard.org/Products/BeagleBone%20Black. Should essentially be a wall dodging, random direction picking 'bot. I'm hoping I can drive the 12V DC drive motors with PWM for speed, and maybe, time permitting, figure if I can relay control the 'vacuum' part of the 'bot.

 

[theoldwizard1]

You know, I didn't think about sleeving the entire shaft; I bought short 1" sleeves to make the added bearing blocks work. How well do you think the 'sleeving' would take threads? Dependent on material type?

If you use "mild steel" you should have no problem threading it.

Welding the sleeve to the shaft takes a good, delicate touch with a MIG or TIG.