Supplementary Post

The top view of the design including the new engine, alternator and batteries will be something like the figure below:

I probably will have to move the front crossmember forward slightly - easy as it is bolted in.  Also, I will probably have to adjust the center cross member - harder as it is welded in - or move the alternator to the rear more if I use smaller batteries.

Currently I am searching for a (hopefully) standard part like the following:

A blade adapter for a mower that slips over the shaft which holds the blade and provides a pulley for the alternator.  Normally these types drive a transmission for self propelled mowers, and the pulleys are about 2.5 inches in diameter.  If the engine turns at 3150 RPM, the Alternator should turn at about 4500 RPM for peak efficiency, I'll need about a 3.75 inch diameter.  I'll probably have to make or modify one.  Some of these are cast pot metal, but some are steel.  I could cut the pulley off and weld on the correct size worst case, but for now the search continues...

The last few days have been more about thinking hard about the next few decisions, and buying a few more of the remaining items.

The chassis is done, and the battery tray (temporary) is in place (no pics, sorry).  This led to the hard thinking of what battery do I want - exactly which ones and how will they be mounted.

I was originally going to put two old deep cycle batteries in and press an old scrappy lawnmower deck into service, but both of those choices seem to be a lot of work that would have to be completely redone at some point.  Besides, that old mower is really a piece of junk anyway.  With a pair of batteries, I could get one cutting done, then they need a recharge.  If I get too far from the house and run out of juice, I'd have to tow it back.

The final plan is to have batteries, an alternator, and an engine with electric start/kill switch/pressure lubrication.

It occurred to me that I can use smaller ( lighter, cheaper ) batteries if I run an alternator.  On average, if the batteries remain fully charged, or nearly so, I can run much longer with less worry.

If I'm going to make the drive system for an alternator, I really only want to do that once so why don't I get the final stuff now.

1) New Engine - a Briggs & Stratton 121S75-2119 new from a surplus house.  Full pressure lube with oil filter, 12V electric start, 3150 RPM, 190 CC OHV 8.75 torque.  This is roughly what used to be called a 6 HP on a higher end mulching self propelled machine, a beefy one.

2) 24 V alternator modified single wire with a bidirectional fan as in this application it will run CCW opposite what most cars run.  It was cheaper to order from Northstar Auto Electric in Macedon that buy it online.  It is a modified Delco (GM) 10SI frame, one of the most popular styles ever made.

Both of the above will be in first thing next week, right after the Holiday (New Year).

With an alternator, I can avoid spending extra on deep cycle batteries and just use regular auto starting batteries.  Deep cycles like to be nearly fully cycled where auto batteries do not.  I can find cheaper and smaller ones, saving weight and money at the same time.

Also, with an alternator, I can reinstall the motor brakes as they draw current 100% of the time when moving, a luxury I initially thought would be bad if running straight off battery.  Now, if something goes haywire on the hill, the mower won't roll away in a fault condition.  That is probably a nice feature...

Well, we've all heard the saying "One Step Forward, Two Steps Backwards".  I'll come back to that in a bit...

Final Drive "Done":

Cut the chains to length and installed them.  Had to run some errands this afternoon anyway, so picked up some longer M6 hardware at the HW store plus a bunch of nylock style lock nuts for the 1/4 and 3/8 motor brackets.  This way they won't (hopefully) vibrate loose during operation.

Here it is installed and tensioned:

The board is just sitting there, it isn't holding anything up.  It is a test piece for the eventual battery tray, though I might add some supports for the motor end so all the weight isn't cantilevered so far.  Those motors are quite heavy.

Back to the lesson of the day from the opening statement - a keen observer may notice a notch in the aluminum angle that wasn't there previously.  It was an attempt to create a little chain clearance by cheating.  I didn't check the clearance after I moved the motor orientation and the chain hit the frame in the extreme adjustment position.  I didn't want to remake the motor plate, so the notch was born.  It mostly solved the problem, but it still bugged me - so I remade the motor plates 1 inch longer.

This photo shows the final corrected plate with the old one on top for comparison.

The remake also allowed for the addition of a little extra material around the mounting holes at the intersection of the vertical plate, to prevent breaking out the holes under the torque of bending the top plate under load.

Drive Sprockets:

Almost forgot about these.  I had some free time after dinner.

Instead of broaching (read: I don't have one) or filing or hacksawing :-O  I decided to plunge a 0.187" end mill to make a "mouse hole" approximation of a key slot in the tapered bore of the drive sprocket.

Tried to take a pic to show the sprocket and the shaft, but the quality control inspector kept getting in my way.  His name is Warrior ( Warry ) and he apparently likes the nice crisp corner.  He is diabetic and almost died when he was a kitty, he might have a little brain damage as he 14 but still acts like a kitten.  He is super affectionate.

"It's mine now"

Not sure what that look means, I'll take it as approval.

The shaft is tapered with a woodruff key, the lock nut and washer hold the whole mess together.  The lock nut is is one of those where the nut is crimped slightly to distort it.  It is not going anywhere, this shaft used to hold the whole wheel on in the wheelchair application.

Now on to the chains, battery plate, and so on.

I'm considering using a piece of plywood as a "temporary" plate across the back of the frame to hold the batteries and wiring.  Eventually I'll make one out of sheet steel as it will also form part of the rear mower discharge.  It will allow me to test the drive mechanism enough to be sure the input design parameters are correct.

Motor Mounts...

Angles from the frame to rear plates, slotted to allow tensioning the chain.  These slots go to the frame allowing front back tensioning.  They are 0.375" wide and 0.75" long.  They use the rear most unused holes in the frame that were used originally to hold the frame together when welding.

Angles in place to test fit & alignment.

Motor Plates mounted, at this point the angles also have horizontal slots where the motor plates can be shifted left right to allow the chain to track true.  All the hardware here is 0.25" the horizontal slots are also 0.75" long.  The plates are made from the 0.375" jig plate I mentioned in an earlier post.  The hardware into the motor gear box is M6 and I did need to replace what was there with longer ones to accomodate the plate thickness.

Front view of motor mount

Next up is cutting and fixing the chains for the rear drive sprockets.  Happy Holidays.

With the axles finished, we can start assembling stuff to verify the motor mount design.

The keys for the gears were cut from a piece of 3/16 spring steel keystock.  Eight pieces 0.75 in long, and two pieces 1.0 in long.  Each was lightly filed after cutting to length with a hacksaw in the vise.

Each shaft sticks out 4.25" to allow 0.125 clearance to the bearing and 0.125 for the axle to stick out of the wheel hub.  The core of the wheel hub is 4.0 in long.

The chains were cut to length a few weeks ago and bagged in light oil.  After assembling all the sprockets, shafts, keys and wheels the setscrews were tightened on the sprockets and the bearing blocks.  Adding the chains and the master links, it's starting to look interesting.  Here are a couple of views:

The motor mounts are next.  The jig plate from Friday was cut down into two long strips using a recip saw.   Cut nice, but somewhat inaccurate and crude.  I cut them wide then milled them clean and square to 4.25" each.

I need two pieces for each side, one 3.125" and one 7.00" long.  I could do the recip again, but it is loud and messy.  I don't have a bandsaw, but I know you can cut aluminum with a circular saw or a table saw. Both of these are kind of dangerous if the material kicks out, or if the saw kicks out of the cut.  However, I do have a 12" chop saw!  The blade rotation loads the part against the fence so is much safer.  A quick trip to Home Despot yielded a new blade:

It's a Diablo D1296L.  The pic is the right one, but mine says "Laminate/Non-Ferrous" on it - they are the same blade.  A high tooth count triple chip blade with a narrow kerf.  It cuts through the jig plate like "butta", but it makes a storm of fine aluminum chips.  Even with the dust collector running, wow, I have some vacuuming to do...

I cut the two pieces off with just a smidge oversize and cleaned them up in the mill.  If I wasn't too particular, the cut from the saw would have been just fine.  It truly is amazing how easy and clean it cuts.

I printed the drawings for the mounts, all the bits are cut to size, maybe tomorrow I'll bore all the mounting holes, slots and such and get them together.

Finished Wheel Shafts/Axles

Last post the keyslots were cut.  The key end was faced on the lathe prior to key cutting, but the other end was wild, just a saw cut.  I didn't have a nice way to cut them to an accurate length.  I thought about carefully saw cutting them then facing them to final length, but that isn't very easy to do repeatably.  Instead, I ordered a couple of parting tool blades, or cut off tool blades from Enco.  They had a nice sale earlier this week.  I also finally got a set of decent parallels for the mill.  I fashioned a simple end stop in the headstock bore, set to 9.375 inches and cut all the shafts to length using the new tool.  It is 0.0625 wide, imported.  I had to sharpen it, but it holds its edge well if you use cutting oil.  Leaves a nice finish too.

Marks to verify length before cutting

After

Pardon the small pip, I didn't align it too well, but good enough for this work.

Back to the mill to drill the cross hole to retain the wheels.  0.25" hole, on center using the same setup as the key slots.  0.5" from each end leaves about 0.125" sticking out of each wheel hub ( I think it looks nicer than just flush ).

Short 0.25" drill in a collet is very accurate and doesn't walk off the shaft.  I set the center by measuring to the edge of the vise with the caliper.  Yes, that is a piece of wood as a parallel.  I didn't want to cheese up my new ones yet, and for a simple cross drill into a sloppy wheel hole a fraction of a degree error won't be noticable.  It's a sturdy piece of oak I planed true.  Besides, if I miss nothing gets damaged.

Final Product after deburring

Lastly, I scored some nice 0.375" aluminum jig plate at Klein Steel Direct.  They had some various extrusions that looked interesting, but then a found a box full of customer rejects of the plate that had been partially machined.  A nice manageable size and a couple of bucks per pound.  I got three pieces for this and just to have, they are about 12x18 inches or so, a nice size to work with.  They will be used to make the motor mounts, the next phase of this project.

Back to it.  The lathe was a "necessary" distraction, but it took a few weeks away from the main event.  Now that it is running, or enough so to do work, this project can advance.

The tapers in the drive gears have been completed.  Measuring the motor shaft and doing a little trig, the taper angle was determined to be just about 6.97 degrees - we'll call it 7.  Still need to cut the  internal key slot, but I have to think about how I want to do that.

Two Gears, one on motor other on the shaft to show fit

The rest of the drivetrain also needs keyway slots, but they are easier.  Each wheel is driven by sprockets with 0.187" keys.  Each 0.75" axle was faced off in the lathe on one end, then set up in the mill to cut the slots.  I found an appropriate end mill, zeroed it to the top of the shaft, then set it to -0.098" a little more than half the key width accounting for radius of the shaft.  Total slot length needs to be about 4 inches, cut in one pass at slow feed rate - bingo - 5 more to go...

Facing

Milling

Final Product

The fit and centering is perfect ( if I don't just say so myself )

On to the rest of the shafts.

Next up is cutting them to final length, facing them off, and cross drilling for the wheel hubs.

Still here, didn't forget about this project.

Check the lathe page, that's where my focus has been lately. It is now running and with some final tweaks should be fully online this week.

The plan is to finish the motor mount design as well as machine the internal tapers on the drive gear sprockets to match the motor shafts ( hence the lathe project tangent ).

Stay tuned...

Not too much going on last week or so.  But, check out one of the latest distractions:

LATHE

When we last left off, the frame was welded and that was the end of the weekend.

This week, I had a little roadtrip that took much of the weekend away.  However, progress is still being made.

On a slight aside, I managed to find a lathe locally to supplement the shop.  I've been looking for just the right one for quite some time and mananged to get lucky.  I am supposed to pick it up tomorrow, and if I can get it back together in time it will be useful for the upcoming axles.

The frame has been primed and painted.  A number of coats of black gloss in between minor episodes of rain this week, plus a few days to cure to allow handling.  Nothing worse than sticky Rustoleum.

Additionally, I finished the extra bits of frame for the front bearings and painted them as well.

The bearings were loosely mounted, and here is the trick to getting them aligned properly.  I use a long shaft that goes through both sides.  This aligns them all to a common center.  By adjusting and measuring the shaft to the frame, it can also be squared up to the frame as well.  Tighten everything up and slip the shaft out, presto.  In some cases various tolerances made it slightly difficult to pull the shaft out, but not impossible.

In the photo above, the left (front) bearings are being aligned.  The middle and right (rear) are done and tight.  In each of these, the rough cut 3/4" axle stubs are inserted.

The axle stubs will be trimmed to length, faced off, crossdrilled for wheel retention and keyed ( slots ) for the chain sprockets.  The keyway will be 3/16" to match.

Flipping the frame over and slipping the wheels on allows for a better visual of the final goal:

This allows for the sprockets to be fitted and the roller chain cut to length.  Since I don't have a link breaker, I carefully cut one side link and bent the link to free it from its pins.  This made for a clean break, quick and easy.

Adding the masterlink allowed a test fit of the sprockets that connect the axles together.

Motor mount brackets will be designed and fabbed to fit.  The goal is to allow adjustment front to back for tension and side to side for alignment of the sprockets.

Frame Welding

Cold today, no rain, but damn it's like 40 outside.

From last night, took the frame and set it up flat on the floor to check the dimensions.  Each corner and joint was made flush and the bolts were lightly tightened.  Check and adjust the diagonals to 47.5" ( the design is 47.5041" - close enough? ).  Adjust the rear inner rails to 2.45" inside to inside edges.  Tighten everything down snug, recheck.  Added a diagonal piece of angle with a couple of clamps to hold it square.  Check again.

Changed the wire on the welder from 0.023" to 0.030" so I can get some penetration.  I think the last thing I welded was sheet metal.

Take everything outside to avoid sparks creating unplanned emergencies and check the measurements one last time.

Remove the clamps and bolts, presto.  The front crossmember is still bolted.  The design allows for easier service of the mower and engine by removing this if necessary.

The welds had decent depth and look OK.

Checking the measurements and flatness - dead on!  When welding, I spread them around a bit so as not to heat one area too much.  I've turned things like this into potato chips before.  This way seemed to work pretty well.  Probably didn't hurt that it was well clamped and bolted.

I'm going to think about whether I want to weld the battery shelf in or bolt it, then I'll paint this to keep it from rusting.  Probably another day, it's supposed to warm up a bit later this week.  It is better to let the paint dry outside, it keeps the peace in my house.

Frame Start

Rainy and cold today, good day to work inside...

Finished cutting to rough lengths, clean up the ends and drill holes in the frame tubing.

Mockup the gears to check the spacing in the design.  Much easier to change now rather than after welding.

Loosely assemble the frame.

Tomorrow, will check it over against the drawing and possibly finish it.

Drive Basics

Actually, I have been thinking about this for over a year, but only recently started to put a serious effort towards it.  I had originally wanted a tracked version, but exhausted finding a cost effective source for tracks.  Some folks have made their own by machining thick rubber strips and gluing them together.  I really didn't think this would stand the abuse of rough terrain.  Someone suggested using V Belts with cleats, but that might be too aggressive.  I'm still looking.

So, back to the 6x6 idea.  What really triggered the whole project is the availability of certain key parts, namely wheels and motors.  Tires are expensive, times 6 and you get the idea.  Wheelchair motors are also expensive, but EBay is the solution there.

Tires - I came across some nice Carlise Super Lug 13x5.00-6 tires at Surplus Center for $32.95 a pair.  They have a 3/4 bore hub.  There are also individual ones for slightly less with a 1 inch hub, but I didn't want axles that big, nor do I want to sleeve/adapt them.

Motors - Searching EBay and reading a lot about wheelchair motors yielded a pair of Sunrise Medical S525 motors:

They aren't "perfect" but the price was right.  Finding specs for these things is nearly impossible as they are typically customized for each manufacturer.  These are ElectroCraft 24V DC brush motors into a roughly 18:1 right angle gear box.  The shafts (after removing the hubs) are tapered, but I can deal with that.  Ideally a straight shaft is easier to deal with, but again - price.  These things are heavy.

Many different chair manufacturers use different diameter wheels, spec different speeds and weight capacity.  I chose a taller gear ratio 18:1 for a faster shaft speed so I could then gear it down myself.  This minimizes the torque load on the motor itself, and thus the current.  If I had a slower motor, the final drive could be closer to 1:1, but the gearbox torque specs are relatively constant no matter what the ratio, so to avoid running into that it seemed best to go this way.

A quick set of Excel calculations of total weight, desired speed, angle of climb, etc. yielded a set of guidelines for maximum torque required as well as the tractive torque that can be delivered to the ground at each wheel.  It doesn't do any good if you need a ton of torque, can supply it, but the wheels spin and just dig in.

From this evolved a design.  The goals are:

• 6 wheel drive
• Tank type steering
• 24 VDC drive system
• Gas powered 22 inch mower, adjustable height up to 6 inches
• Radio Control ( with throttle cut safeties )
• optional additional channels for additional functions and maybe telemetry
• optional alternator to charge drive batteries

Below is a snapshot of the CAD design ( I use AutoCAD ).

This helped to guide drive design and bearing selection.

Roller chain is straighforward.  17 tooth drive sprocket, 60 tooth driven sprocket, 20 tooth wheel to wheel connecting sprockets.  I sometimes call them gears, but I mean sprockets.

Bearings are 3/4 inch bore pillow blocks.  They are relatively mounting insensitive and are greasable/sealed units.  I toyed with the idea of discrete bearings, but the mounting is important and the ability to grease them is too.

Again, a great source for all of this is Surplus Center.  I ordered all the bearings, sprockets, chain and master links from them.  They are the cheapest I could find, and the quality is decent.  The bearing blocks were about $5.60 or so, compare to $30 to $75 elsewhere.

The frame is 1x1 inch steel tubing, and the axles are 3/4 inch cold rolled steel.  I purchase my steel from Klein Steel Direct in Rochester, NY.  Typical prices are about 70 cents per pound.  24 feet of tube and 6 foot of shaft cost about $28.

I'm cutting the steel roughly to length with a recip saw, then cleaning up the ends separately.

TTFN

A Mower Project?  Why not?

As if you can't tell, from the last post on my other blog ( 2012 ) and my nearly complete lack of presence on other media.  ( yes, I've been on facebook since 2008, but with what like 3 posts maybe ) I don't do this a lot - be patient.

I have a section of really steep hill that I've planted grass on and like to keep mowed.  It used to be a collection of brambles, rocks and poison ivy, but finally cleaned it up a few years ago.

I used a string trimmer for a while, but afterwards it's like I've been running a food processor with the lid off.  I had grass and other odds and ends all over me.

I created the "4x4 Mower" which really isn't 4x4 or any drive at all, but it has cool wheels.

The idea is that it rolls easily over bumps and small holes, allows for a higher cut height, and mainly I don't get green stuff all over me.  The wheels are from Tractor Supply.  The axle diameter is identical, but I had to create extensions on the lathe to allow for the wider wheels, essentially threaded stand offs.  The mower has a new cut height of 5 inches.  The mower is a side of the road rescue unit.  It is on its third engine now.  I don't think the lubrication works well at steep angles ( more on that topic later ).

The hill is steep enough that it is best (read safe) to cut across it, back and forth, top to bottom.  It is tough on the ankles, but doable.  It is easily 45 degrees at some points, maybe more.

I've read about commercially available steep slope mowers, but they are many thousands of dollars.  Places like EvaTech and the now defunct (?) Summit Mowers have some examples.  A few robotic enterprises have also built or can build various versions to suit your wallet, eg. SuperDroidRobotics.

The pictures are detailed enough to get a general idea of what they did.  It seems simple enough.  A frame, wheels, electric motors, radio control, drive mechanism, and a gas powered mower deck.  How hard can this be?

I really like the rubber tracked versions, but treads are about $600 a pair.  Maybe I could find a used pair, but drive is also pretty involved.  Maybe Gen 2.

Enter the 6x6...  a 4x4 is slightly easier, but the wheelbase would end up rather long and the possibility of high centering or scalping the grass is very high.  6 wheels makes more sense with minimal added complexity.

Off to think on this some more...