Axle has arrived; upcoming plans

After a battle with a nasty 48 hour bug this week I managed to snap this photo of the new axle I bought from McMaster-Carr.

Axle
It is partially keyed - 14" on one side, 4" on the other. So, more then enough space for a wheel, drive sprocket and brake sprocket. It is made of 303 Stainless Steel - I'm darned happy because it is shiny, and it's going to stay that way. I would hate having a rusty steel axle and be fighting to remove all the sprockets from it in the future. The disadvantage is that the tensile strength is much lower, but still around 70,000lbs - It seems like a lot to me, but I'm sure the forces in this kind of system are intense.




For scale, the 1" bar in front is 12" long (30cm). The drive motor is properly aligned with the axle sprocket but perhaps too close together, I really need a frame to mock that up properly.

Frame
Speaking of frame, that's my task for this week, to go shopping at Metal Supermarkets, and to get a red flag or something to hang off the metal I'm sure will be sticking from the rear of my car. Thinking 1 1/2 square rather than 1 1/4 most (gas karts) use because of the extra weight I'll be lugging around in batteries.

Batteries
Still waiting for my contact at a certain battery company to get back to me. I have a contact who put me in touch with the sales manager, so I'm hoping to swing a great deal from them. It would cut a lot off the purchase price.
Interestingly I was also told to consider using NiMH - either industrial packs or sub-C cells - and making my own battery pack. Well that's the advantage of talking to people in the know, I would never have considered such a plan.
Apparently on Monster Garage they converted an old Bel Air to run on cordless drill batteries! Have to check that out some time.

Brakes
I've been reading a lot on www.diygokarts.com and a lot of people have been helpful there. A certain member who lives relatively close to me not only offered me advice and pictures of his experience, but also offered to sell me a set of working hydraulic brakes for a steal, only $60! Remember the bike shop earlier quoted $150 for the same exact deal - one set of used brake parts. Different models I am sure, but in both cases, just whatever was lying around.
I'm ecstatic! It might be a pain getting over to see him but totally worth it. I'm sure I will get a lot of sage advice too. Anyone else considering a similar project to this *really* needs to spend time on forums, there are some awesome people on the internet (i.e. in real life, that you can communicate with on the internet hehe)

Trailer
On a completely different note, I have been considering how to move this kart around when it's finished. Most people are settled and build these in their back yards... seeing as I am in an apartment this is a problem.
I have recently realized that my go kart has trailer tires, and the front (will have) actual trailer stub axles. So - get the kart licensed as a trailer, and tow it backwards! I'm thinking to build a pin into the steering mechanism to lock the steering straight for towing, and leaving a place to attach a long trailer hitch arm to the rear of the kart.
The Ontario website does not indicate much in the way of requirements for trailers so I think it should be relatively easy to get it plated.

Until next time...

Princess Auto shopping trip

This weekend I spent three hours (and several hundred dollars, sigh) on a bunch of mechanical parts for the project, and a little in the way of tools. 

I ended up buying the tires that were on sale, they are Carlisle trailer tires, 16.5 inches diameter. Unfortunately they only had 3 in store, so I got a rain check and will have to go back to get the fourth.

I chose #50 chain and a 1"  rear axle. Here are the rear sprocket and the motor sprocket, chosen for a gear ratio of about 2.5. I ended up with 48 and 18 teeth, for an actual ratio of 2.66.

 The rear wheels are on a live axle, so I have to solidly attach the wheel to the axle. I decided to use a small sprocket, and bolt the sprocket to the tire.

 The is just small enough to fit inside the rim, on a 4 x 4" bolt pattern. First I tack-welded the sprocket to the hub, and made sure it was properly seated and square. I drilled 1/4" holes on a 4" circle - the milling machine and rotary table at work came in very handy here. You could do it by hand but it would be *even more* time consuming.

All the sprockets I used are designed to be welded onto the hubs which are keyed to attach to the axle.
So here is the first real welding I have done in a few years, for the rim attachments.
It is fairly ugly, and was hard to take a picture of. A wire brushing would have helped, but I did bang off the slag with my welding hammer. The second hub went much better than the first, but still needs a some more improvement.

Still the first hub. It really is a solid weld, both components are melted and there is decent penetration. I know this is one of the more critical welds in the project for my safety, and I am comfortable with them.

 I then expanded the holes with 3/8 and 7/16 drills. The bolts I am using were designed for tire applications, to be hammered into the hub. Of course the dimensions are not handy; the threaded section is 1/2" but the flat area is 0.53" and the ridged area which provides the holding effort is about 0.55".

I had to use the mill here again to get the dimensions right; I don't know exactly how big the hole was but just over 0.53".

See the ridges don't quite fit? This is perfect. Now you have to beat the shit out of the bold head to drive it into this sprocket, which I swear is hardened steel. It was very difficult - if I made the holes larger it would have been easier, but there would have been less grip strength in rotation.

 Hey, it fits!

Here's the bolt side.
You can't tell but the ridged area is too wide, so the nuts don't completely seat. I need to add spacers for a better fit. I should have used thicker sprockets instead.

Both sprockets together

Hammered-in detail. See the sprocket was deformed by my intense hammering.

Here's the posi-lube stub axle which I will be using for the front axles.

Stub axle detail.Very overkill, but it's a bearing and hub I don't have to assembly. Weighs a ton.

Brass bushings and 5/8" bolt as kingpin. Will use half of each bushing, take the other half for the other side.

Motor sprocket on the motor.

1/8" aircraft cable, and accessories for brake and gas.

1" pillow blocks with scrap 1" bar lying around the shop. I chose 1" axle because the 1 1/4" pillow blocks at Princess were not assembled so I would have had to use a torch I don't have to assemble them.. not fun.

The brake rotor -another sprocket, surprise! with the axle gear.

Both tires bolted to hubs and on the scrap 1" bar again.

Motor and rear axle mockup, again with scrap piece.

Next I have to buy a 1" keyed axle, some keystock, locking collars, and a bunch of metal from Metal Supermarket.

Welder plug installed, brakes make more sense now

 Welder:
$110 later, I have a 40A circuit hooked up for my welder. Plugged her in, and she welded first try.
Of course I checked voltages with a meter first :) I'm just glad the 240 to 208 conversion I did last week worked properly.

Brakes:
In other news, I've been bugging people on the forum diygokarts.com and I've gotten some great help in the hydraulic brakes area. More specifically, how to take hand brakes from a motorcycle, removing the hand lever and replacing it with a different lever, cable-driven by the brake pedal. Perfect!
Now I definitely know what I want to do, I just have to buy some brakes. The person who helped me out might also sell me some, or eBay has a decent selection.

Tires:
Still fuzzy in the tire selection arena. I only have a week left on that Princess Auto sale. Someone on the forum is using that particular kind of tire, but they installed tubes in the tubeless trailer tire, so that he could run a low pressure setup, compensating for having no suspension. According to him, these tires are capable of bending the go kart frame when off-roading at the recommended inflation pressure. Crazy! I have asked for clarification, we'll see what he says.

Work proceeding slowly

So I was home on the weekend for Fathers day, it was a great rib fest - all ten of us!
While I was there I borrowed some of my Dad's tools and picked up some of my own.

Now I know what you're thinking, stealing from my Dad on Fathers day, right? The thing is, he has all the tools he needs up at the cottage right now, the rest were in 'storage' not being used. Except the chop saw my sister and her husband were using.. sorry guys!

Anyways, I have picked up:
Lincoln Electric 'Mig Pak 15' welder
Bosch chop saw
Mikita angle grinder
Welding mask, tool boxes, misc.
Even more electronics junk

Welding to do:
Now I have to get my new 'shop' (read: workplace - thanks for letting me build this at work guys) set up to weld.
Of course the welder is set up for single phase 220, and work has three phase 208, so today I opened the guts of the welder, and swapped over the terminals.

While I was in there, I disconnected the gas solenoid - I use innershield flux-cored welding wire rather than solid wire with CO2 gas. No point in running the solenoid all the time if I never use it!

Now I have to go buy 18 feet of 8AWG four-conductor wire - preferably armoured but I don't think I'm going to spend that much money for something temporary (and in a zero-traffic environment). Also need a two-pole 30A breaker and a box for the receptacle (that I already have)
I hope finding the breaker won't be difficult - it's not a standard home-type breaker with the little metal peg at the bottom, it has a slot that the breaker box pushes inside (so female instead of male). A Cutler-Hammer unit.

Princess auto trip
I live in Toronto, Ontario right now. There are three Princess Auto stores relatively nearby to me. Wouldn't you know that all three stores are equally distant, 36, 36, and 37 minutes travel time - in different directions. Could be worse.

They have some trailer-tire assemblies on sale right now for $50 for tire+rim.
The tire is 16.5 x 6.50-8
PA: 8227175
Of course you should *never* use a trailer tire for a drive or steering wheel on a car - but the go-kart will weight much less than a car, so (at least I'm hoping) the load on the tire isn't too high, and the tire gets a sufficiently good grip on the pavement. They should also ride a little softer than car tires - most trailers have minimal suspension like my kart will, so they have softer sidewalls to compensate.

Other tire alternative:
I'm looking at a wrecking yard close to home in Scarborough, and another much further away. With any luck I'll be able to get a set of used tires from a small crappy car, with rims also already attached. If I'm desperate/lucky I can ever steal the steering knuckle and repurpose it.

Axle attachment:
For the front wheels I'm thinking of getting a trailer stub axle from Princess Auto or the wreckers.
PA: 8217242 1,000lb Posi-Lube Stub-Axle. Has a 4x4" bolt pattern to match the PA tires I was looking at.
For the rear axle, I'm thinking of using the same type of weld-on hub that I'm using for the sprockets
PA: 3845351
then welding a disc onto the hub, turning it down with the lathe, etc. I'm also debating saving time (read: lazy) by using an actual sprocket designed for these hubs, and just drilling holes in it to bolt to the hub, just ignoring the sprocket teeth. That eliminates a lot of machining time -  the hub and spocket have pretty small tolerances where they mate.

So that's four weld-on hubs.
Motor sprocket (18 teeth)
Axle sprocket (60 teeth)
2x tire rims (however many teeth I need to get a size large enough to drill holes through the sprocket and small enough the teeth don't hit the curved part of the rim. Going to decide in-store)

Still need a 1" axle and pillow blocks to go with that.
And a brake!

Brake hunt:
Princess Auto carries cable-powered disc brakes, but they are very expensive for the whole kit.
eBay sellers carry the same thing for half the price or less.

The current alternative I'm pursuing is a hydraulic brake assembly from a motorcycle. I'm hoping to snag the whole thing from a motorcycle wrecker in one piece, so I don't even have to bleed the system. Just have to figure out how to attach the master cylinder to the brake pedal instead of of the brake handle.

Electronics junk:
I brought up my 4x20 character LCD screen so I can have a display for the go kart. RPM, heatsink temperature, current, that kind of thing. The controller board that I'm using (which I designed for work) has a lot of flexibility, including a ribbon cable connector designed for a - you guessed it - LCD screen and some buttons. Note: This was a requirement of the design spec for the board, not something I added on for my own purpose to a work project!

So I'm going to get a ribbon and make up a little board with the LCD, and tack it into the software.
The great part is this ribbon cable has everything, power, I/O and even a PWM output so I can dim the backlight of the LCD screen effortlessly. Gosh I am happy about that.

I need to pick up some metal enclosure for the electronics - the logic board, main contactor, aux relay, precharge resistor, and 18V linear supply. It'd be nice to have this protected from the elements, at least somewhat. I would seal it in a weatherproof plastic box but the linear supply has to dissapate (probably worst case) 10V*0.1A = 1W. Alternatively, just stick 14g of aluminum on the linear supply and it will heat up by 100°C after 20 minutes of runtime too. I kind of hate having to do that twice, the kettle is bad enough. Metal enclosure means I have no time limit here :)
 The IGBTs on the aluminum block will have to remain exposed, maybe a small rain/mud shield.

Kettle design:
As I said in the video, the IGBTs will need water cooling. This project does not call for the complexity of a pump, radiator, etc. so I have decided to use boiling-water cooling. For a current of 200A, 1.5V, 15 minutes that is a grand total of 270kJ.

From the thermal enthalpy of vapourization of water, that equates to 0.12kg of water boiled, or 120mL. 30cm of 1" diameter copper pipe is long enough to contain enough liquid; I will solder the copper pipe to a copper sheet, which is in turn bolted to the back of the aluminum block.
You have to add more pipe than optimally required, since the soldering will involve flattening most of the copper pipe.

I will add a shutoff valves at the bottom of the kettle. This will allow me to drain excess water when I am done driving. To keep bugs out of the kettle during storage, I will either use metal screening to cover the hole, or insert a stopper of some kind.

Summary:
I've been doing a lot of thinking an research for the project, but haven't been posting regularly enough. I'll try to post more often so I don't generate these unreadable walls of text.
For this I am truly sorry.

William

Photo/Video Update

Hi all;

Here are some more photos, but most importantly the video I've promised.

IGBT Motor Controller - Youtube

IGBT Controller with Capacitor bank and wiring

IGBT Controller gate drive circuitry.

Motor upgrade ($$$ ouch!)

A picture is worth a thousand words.. so I'll show you the upgrade first

As a reminder, the old motor on the right was the car starter from the 1999 Sunfire.

The previously-loved motor on the left is from a place in Brampton Ontario.

Anyways, she's a 10" long 7" diameter 24V, 1725RPM motor.

Not quite the beast I was hoping for, but I'm planning on overvolting to 36 to get a higher locked-rotor torque. I think I'll have to be careful to limit the RPM somehow, I don't know if she will survive wide-open-throttle on flat ground (The armature expands and slams into the stator. Poof goes your money.)

Apparently though, everyone in the go-kart hobby arena overvolts their motors - it's just a question of how long you want the motor to last...

I've tested her on 12V using the IGBT controller I haven't even posted on my blog yet. I really need to put batteries in my video camera and actually do some filming.

On 12V the motor doesn't do anything all that interesting.. It's "slow" even at full speed, and doesn't have enough starting torque to even jump a little when I go from 0% to 100% throttle instantly.

Since it is a series-wound motor I'm sure she'll take off with a higher voltage, but I still was hoping for more... These things are supposed to wind up like crazy in a no-load situation.

Onwards!

IGBT Upgrade

It's been a very long time since my last post - I'm no longer broke and was able to purchase some new toys.
I've decided MOSFETs aren't the way to go, because they are too easy to break! I know it is possible to use them, it's been done a million times before, but soldering the SMT mosfets to a copper buss bar with a torch takes a long time, and I've melted the plastic that the buss bars were bolted to.

IGBTs are much more rugged - basically IGBTs are the ruggedness of a BJT glued to the easy gate-drive of a MOSFET.

So I bought a pair of single IGBTs off of ebay
Mistsubishi MG400Q1US41 N-channel IGBT - 1200V 400A

That's right, 400A of switching goodness. Now I need a place to mount them!

So I went to McMaster-Carr's website  to buy some metal. 
IGBT bricks need a fairly flat surface to mount them on, for heat transfer purposes. So I bought a quarter-inch thick, six inch square of aluminum, precision ground to a high degree of flatness
(6.35x152x152mm for the imperially-challenged)
Any warps in the metal means there will be an air gap between the IGBT and the 'heat sink', so the IGBT will be unable to dissipate heat properly.
It is very flat, has very sharp edges, and is one stiff piece of metal - perfect, since it is the structural support for the whole controller.

Then I need some more copper, to connect the IGBTs to each-other, and to the wires. (my mosfet controller used all the copper buss bar I scrounged from home)
The main concern was being able to fit the bar inside the LEM current sensor, its opening is only 10.4mmx20.4mm, so 3/8"x3/4". Of course no-one sells this size, but 1/4x3/4 is easy to find. I got a three foot length.

My apologies for not having pictures of all these components separately, but I hope these make up for it:

The blue brick is an IGBT snubber, a 0.68uF cap, 1250V designed for this application. You mount it directly on the IGBT, across the switch. It dampens the energy spikes, preventing the voltages from getting too high (well not preventing, just ... damping) although it wastes energy every single cycle (0.5C*V^2 joules - 8.5W at 50V and 10kHz). That's a lot for a cap, but nowhere near the power getting to the motor (fingers crossed).


The silver strapping on each IGBT is shorting the Base (Gate) to the Emitter lead - thus turning off the transistor, as well as protecting the gate from ESD - I would cry if I broke one. The gate on modules as rugged as this is still *very* fragile. 20V and *poof* when it can withstand 1200 on the other two, pretty crazy.

Circuit:
Exactly the same concept as before. One transistor that pulls the M- bar to B- and one diode that allows freewheel current from M- to B+ when the transistor is off.
IGBTs have a reverse diode like a power mosfet does, but it is much a better diode, rated at the full 400A, with a pretty low voltage drop (0.3 on a meter test, but that means squat in the hundreds of amps)

Gotta run! Expect more frequent posts in the near future.