Little girl's off-rail industrial hand car

[Elliot]

Also doing it wrong. Four ATV tires, effed-up steering geometry. $10,000 worth of company time by professional fabricators, and it worked like crap.




I replaced the tires with much taller ones, and converted the front to a single wheel. Woosh.

[BoyScoutGirl]

Thanks for the explanations!

Right now the group is split between plan E and plan F. I currently prefer plan E because I love the idea of having to coordinate four people to turn. Sure, we'd be weaving all over the place, but it would be fun. I also like the idea of tighter turns and no distinction between the front and rear of the vehicle.

However, it seems I may have fallen prey to feature creep. Because plan E requires two pumps, there doesn't seem to be a good way to power plan E with only one or two people. Having one person's arms pump the left and right levers at different rates is really too tall an order, especially if you have to coordinate with someone across from you who's attempting do do the same.

Much to ruminate on!

[Elliot]

Maybe some Complication Creep also?
Plan E (whether two or four casters) with two people... each person pumps one side. No need for both to pump both sides. But maybe I misunderstood you.

One person might require quite a bit of practice to steer Plan E (2 or 4). But how often would you be alone on it? Just get the thing out in the street and ask people where they want to go -- and in 30 seconds... off you go with a full crew.
At least that's my experience with my own four-seat pedal-vehicles.

Considering that "strangers" may/will ride this thing, you might want to pad the pump handles real well. Leave "slots" in the padding for the hands, but lots of padding to minimize broken noses and teeth.

Good fun, this brainstorming!

[BoyScoutGirl]

Oh, how embarrassing - of course two pumps wouldn't require four people!

I might have a smattering of book smarts, but I am going to hang out here a lot longer before I develop a lick of common sense!

Definitely planning to minimize broken teeth! Also, skinned knees: actual handcars' pump levers went down past the knees; we're probably not going to allow quite such a large range of motion. Other precautions include making sure there's a enough of a lip on the car that we don't just keep backing our stances up until we fall off the front/back of the car. If we go the see-saw route with two pumps, we'll need to allow enough room to not knock knees.

[BoyScoutGirl]

Ah, and one more thing:

Drive (gear) ratio changeable by re-positioning crank pin.

We tried mocking this up in Shapeways, but we seem to have run into a problem: if the length of the connecting rod, the length of the crank arm, and the distance between the connecting rod attachment on the lever and the lever fulcrum are not carefully balanced, it seems to affect the balance of how far 'round the pump lever arm swings.

I haven't mocked it up myself, but my friend reports that only adjusting the effective length of the crank arm can make the pump lever dip lower and raise higher on the right than on the left. I have a hard time visualizing this, but I think it may be due to the fact that the crankshaft was not lined up directly under the pump lever fulcrum. Most real handcars have the crankshaft offset from the pump lever fulcrum on the opposite side of where the connecting rod attaches to the pump lever. In other words, S and C are on opposite sides of the vertical here:


I don't know why this is, unless perhaps it was just to get the sprocket with the crankshaft far enough to the side so it would directly engage the teeth on the axle without having to use a chain. We were thinking of having the sprocket with the crank directly below the pump lever fulcrum, but that definitely was not the historical trend...

[Elliot]

The original Exercycle. Note where the on/off switch is. I picked up one of these for $20 at a flee market. First time I naturally leaned forward to reach for the off switch... the handlebar of course came the other way. Must have been invented by Charles Darwin. Sold it for $100.

[Elliot]

As for George Sheffield... seems to me you understand the dynamics of the geometry pretty well!

[Captain Goddammit]

If you want it to have the look of the Sheffield illustration, but not confined to a set of tracks to run on, it pretty much has to be a four wheeler with one drive axle and one steer axle.
Having the wheels outboard of the platform seems a very good idea, better stability and you can use 20" wheels instead of 16". Or even 26". I think everyone will agree that larger wheels always work better on the playa. The larger the better.
A two-axle layout makes scrub steering more difficult. I think if you use scrub steering it may work better for the rear end to steer.
Lowering the deck and having outboard wheels would mean you'd have to go with the car style steering where the wheels hinge on each end of the axle, rather than the little red wagon style steering where the whole axle pivots in the center.


I'm starting to think using a freewheel hub would be a good idea, so It has the ability to coast instead of the pump handles always having to pump whenever it rolls.
Braking can be easily be accomplished with bicycle type hand brakes with the brake levers mounted on one of the pump handles. If you have separate left and right brakes I think it could be a great advantage for making turns.
If you have chain running to the drive wheels you could pretty easily use three-speed (or more) hubs, with bicycle type twist-grip shifters on the pump handles and have your gears. Gears are often a good thing.
However, the freewheel and/or multi-speed hub setup would render it a one-direction vehicle. That may not really matter much.

[ygmir]

as relates to range of motion for the levers, remember that leverage is what will make the driving easier, but as the length increases, so will the range of motion, unless you put some sort of "stops" in as limiters.

[Captain Goddammit]

You can't have stops on the pump levers or the cart will stop, if I understand what you mean. You just have to get the stroke right.
A chain and sprockets somewhere in the drive system would give you an easy way to adjust things.

[ygmir]

You can't have stops on the pump levers or the cart will stop, if I understand what you mean. You just have to get the stroke right.
A chain and sprockets somewhere in the drive system would give you an easy way to adjust things.

good point. not sure why I was thinking hydraulic, when talking about pump.
yeah, chain and sprocket for leverage, too.

[tamarakay]

Now this is an awesome thread

[BoyScoutGirl]

Basic shape:

Shown with
6 x 4' platform (1.5" square tube)
16" diam x 4" wide wheels (trailer wheels, pretty cheap)
3' tall tower
4' lever (2" square tube)

I love the look of these 24" wheels, but they're narrow (1.75") and pretty expensive, so we're wary. Any comment?


The challenge continues to be steering. We're throwing all in behind four wheels in a rectangle pattern, having given up on two pumps and reversible steering for the time being. We've only got a few months to build this thing, after all!

Steering and braking ideas:


As shown above, we're currently planning on powering rear wheels on a split axle. We've been looking at sourcing parts mostly from standard bicycle parts (crank, sprocket, bearings). Each rear wheel will have a freewheel sprocket, which (I believe) means we'll be powering turns from the inside wheel only.

The sketch shows steering by a coordinated yaw movement of the pump handle, but it could just as easily (or even more easily) be accomplished with a tiller. We're less worried about that end than the wheels themselves at this point.

Right now, steering is the front two wheels. The sketch was made with casters in mind, though now we're looking at go-kart steering with trailer parts. We think we've got it where each front wheel can roll freely with respect to the ground (trailer spindles) but is locked to the other front wheel with respect to angle. However, go-kart steering appears to be what was attempted in several of Elliot's "Doing it wrong" images, so we were hoping for feedback.

You'll notice that we've got the wheels in wells that are above the floor of the handcar. This will limit our ability to angle the front wheels. How much freedom of rotation should we aim for? One of our guys things 5 degrees is enough, but 5 degrees on a six- or possibly eight-foot platform means a huge turning radius...

[Captain Goddammit]

5 degrees will result in a bus-like turning radius, you'll definitely want more.
There is a chain and sprocket link in my MV's steering (as well as gears, rods, u-joints, etc.) and it works great. I'd try to minimize or eliminate cables in the steering, they tend to be sloppy and troublesome.
On your rig I think I'd use all solid linkage. You can make a bell-crank up front to transfer fore & aft movement to side-to-side movement to do your steering.
You could probably cut tie rod ends off junkyard cars and weld them to the ends of some pipe, like gas or water pipe, to make dirt-cheap custom linkage that is super strong and pretty slop-free. You'll need a cordless sawzall or portable torch to do it at the Pull-a-Part. Or maybe there's cheap go-cart stuff you can just buy.

Definitely work on getting the Ackerman angle correct in your front steering. The inside tire in a turn needs to turn sharper than the outside tire. You get that right by drawing a line from each front spindle to the center of the rear axle. Your steering arms that come from each front spindle - that your tie rod attaches to - need to follow that line, as viewed from above. Don't just make the front wheels turn exactly parallel to each other or you will have unnecessary drag when you turn, and turning will already be harder than it should be due to the inside tire doing the propulsion.

The "Tuff Wheels" really are tough, I don't think you'd break them and you can easily use bike freewheels with them, but you can most likely scrounge up trailer or small car wheels cheaper. Not a bad idea, I wouldn't argue against it, but it keeps getting heavier... it'd be stout though. And that's good. Inflate the tires extra-hard, it'll roll very significantly easier.

I think the idea of having the pump handle pivot to do the steering is a great idea. Only thing I'd suggest is having only one side steer, leave the other side fixed. Less confusion would be involved in steering the thing, no consensus among four drivers that way. Build the pivot really stout. Then cut it off and throw it away and rebuild it with heavier steel and make it way stouter than that. I did three steering systems on my MV before I was happy with how strong it was.

[EGAZ]

........ .......

Love this thread

[BoyScoutGirl]

Captain, we're grateful for the advice and guidance. Thank you again.

We did think about go-cart parts but were worried they wouldn't be heavy-duty enough. This leads us to the question of weight.

The 3D model above is estimated at 160-180lbs total, assuming we'd use 1.5" square tube with a wall thickness of 0.062". We could make the whole thing about 30 lbs lighter by switching to 0.050" steel, but we worry about accidentally burning through such thin walls while welding.

Is 1.5 x 0.062" overkill? As it's wisely been said on these forums before, overkill is still kill.

[Captain Goddammit]

I wouldn't compromise the strength of the thing over 30 pounds, stouter is better.

[EGAZ]

I agree. Anyone that is decent with a Mig welder should have no problem welding it up. might need to drop to .035 wire.
If they know Tig, all the better.

[Tiahaar]

Should work! Go with 24x3" tires on those wheels if you can, something like the Sunlite Cruiser Flame 24x3".

[BoyScoutGirl]

We ran the numbers again and it's even less than a 30 lb difference, so we're almost certainly going to opt for stronger. We also did some tests of how much the metal deflects under anticipated weight stresses. In other words... we've been buying short sections of tube, suspending them from the ends, and standing on them. You know, for science!

Thanks for the reference, Tiahaar. I'll investigate see if we can fit those on the Tuff Wheels - I think they might be too wide. That said, the Tuff Wheels are much more expensive than trailer tires, so I'll have to see if the added cost is worth the sweet aesthetic.

As for welding... it'll be my first time but I already know of a studio where I'll go for training first. One of the other guys on the project has some welding experience, though which type of welding I don't know. Stick welding, maybe? Part of the decision there is going to be what kind of equipment we can get our hands on, which will depend on our workspace... which we're still working on finding, unfortunately. As a group we're not against purchasing the equipment.

[EGAZ]

I strongly suggest you use a mig or wire welder to weld it up. It can be done with a 'stick' welder. IF the person welding has some experience, uses very small rod and has a AC/DC +/- welder with 'dial adjustable' amperage setting. Not a rotory switch. It will be tougher not to blow holes with an AC 'Buzz box'. If you or teammate has done stick welding then using a wire welder is relatively easy once you set up the welder and do a number of practice welds.

AC/DC Pos/Neg stick welder Notice the adjustable dial for amperage setting (hand crank on top. Scale in upper left corner). This allows more fine tuning than a rotory switch. And the leads can be moved to the proper ports for 'Pos' or Neg' welding. (lower left corner) This would be a 'borrow thing' as they are not real cheap.

Basic AC buzz box Limited choices for amperage settings and many times a 'little bit' more or less is required. Though can be over come to some extent with proper arc control. IE: lots of stick time. Cheap to buy but not for this project. Good for down and dirty welding.

Basic wire welder (Mig) with shield gas regulator These can be found relatively cheaply on CL or Ebay or if you have a Harbor Freight close by. They come in two versions. One is a 'Gas Shield' welder that requires a tank of Argon or Argon/C02 mix. The wire is 'solid' or no flux core. The other is no shielding gas but you must use 'flux core wire". Wire for both come in different diameters depending on the thickness of the material being welded. Shielding gas will give you a smoother bead and will have less clean up. Flux core will require more cleanup due the "spatter" it generates.

Note the Spatter on both sides of the weld?


No spatter or much less with shield gas.


Lots of sites on the net to show you how to set them up and to learn how to weld. Do you have a Tech Shop or Makers shop that has welding training? If so I would recommend taking the course. If you were in Phx I would help you out. Got a Gas Shield wire welder and a buzz box in the garage.

[Captain Goddammit]

I would suggest you go grab this immediately:
http://seattle.craigslist.org/est/tls/5558485280.html

[Dr Helix]

I would suggest you go grab this immediately:
http://seattle.craigslist.org/est/tls/5558485280.html

Pretty light there Capn' I've got two of those and I don't like to weld anything over 1/8"-/3/16" And if you do, go with .023 NR-211 innershield wire. Eliminates the need for gas as the flux is inside the wire. That'll get you the best bang for the amperage. Yes there's slag but at least you'll get some penetration.

[ygmir]

I would suggest you go grab this immediately:
http://seattle.craigslist.org/est/tls/5558485280.html

that's a sweet deal, and a good welder, good call Cap'n!
jeeze you (a coupled of you) guys, this is not rocket science. She's going to be working with nice, seemingly new mild steel, not so thick it requires much amperage at all, but thick enough it's be easily done with stick, too. I'd use 7018 probably, and I don't see at all in this application how it'd matter DC +,-, or AC. Mig is nice, but not necessary.

[Jackass]

Better

[ygmir]

that's the one I have, Works nice, but still for things needing to be really strong I feel better with stick.
I have a Miller Bobcat 225 and a buzzbox.

[Captain Goddammit]

Remember this is just a low budget project with pretty light material.
I think a little 120-volt wire-feed would be just the thing, it's easy to learn to use, plugs in anywhere and it's plenty powerful to build this thing.

[Jackass]

The 120 VAC will do the job, you just have to be patient and slow since it takes a while longer to get things really cooking.

[EGAZ]

I'm with Captain. Its true these little wire welders don't do heavy gauge very well. At least not without joint prep. (chamfering, multi pass) but it just fine for their 0.062" wall tubing. If you are going to be welding 1/4" thick or more than a much larger wire welder or stick is the way to go.

Stick welders and large wire welders require 230Vac supply. These little ones only 110Vac.

Flux core will work, gas shield saves some work and the welds look much better.

Watch the duty cycle as JackAss said. I tend to work mine a bit too hard. Had to add a fan....

That CL welder is missing the wire brake on the wire spool, (or the wing nut that goes on or both). The brake keeps tension on the wire so it doesn't loop like in the pic.
There is also a small piece of felt that clamps around the wire before it goes into the feed motor. Not a big deal but keeps crap from, going down the line set.
Be sure it comes with the shield gas regulator.
I don't see a argon tank either. CAn be rented from a welding supply place but better to come with one.
It also included a complete Oxcy/Acet torch set. Nice to have.
The two regulators for the torch set will not work on the wire welder!!
I see some refrigeration gauges in the box. unless that is the shield gas regulator....

If you look at it be sure to fire it up. The wire should move evenly & smoothly. Change the speed setting to be sure the motor tracks. Make sure the gas solinoid operates when the trigger is pulled. Do a few welds.

And be aware the wire is HOT when the welder is turned on. Meaning it will spark when touched to metal. (when grounded with the ground clamp) The trigger just activates the wire motor and gas solinoid.

When welding on the project get into the habit of cutting the end of the burnt wire off before starting each weld. Help at the start.


....jeeze you (a coupled of you) guys, this is not rocket science. She's going to be working with nice, seemingly new mild steel, not so thick it requires much amperage at all, but thick enough it's be easily done with stick, too. I'd use 7018 probably, and I don't see at all in this application how it'd matter DC +,-, or AC. Mig is nice, but not necessary.

True its not rocket science but if one has not had a much stick time a wire welder is easier to learn on. You, me, captain, JackAss may be able to weld it with a stick, (I would go 6013, its only .062 wall) But if her friend is a rookie, he will blow holes or have bird shit for welds. Additionally they can sell it for what they bought it for when done. Stick welder move more slowly as there are many on CL all the time.

[Jackass]

I've never welded stick, just light- medium duty MIG stuff, mostly with the millermatic 175. It does everything I need, and then some. Great machine. I tricked mine out swapping out the stock cord for an 8 AWG 16' cord, now I rarely need an extension!