Monday, September 1, 2008

Lower Rear Rack, I

With the 3-day Labor Day weekend, it was a good chance to tackle the biggest single fabrication job of the whole project - the lower rear rack. This is the rack which is sunk below the floor of the rear compartment. After some thought, I decided to go with 8 batteries in this rack instead of 9 - it yields a symmetrical design - which means that many parts are mirror images of another part, which makes it much easier to fabricate. Here are the plans, done in Google Sketchup:

Here is a Sketchup-generated picture of the designed rack:

One thing not shown in these plans and pictures is the sheet metal box that will be welded to this rack - I don't want water getting into the passenger compartment.

The first step was to start on the lower portion of the rack. I cut out the 8 pieces, sanded them, and test fit them:

They were then welded together (along with the diagonal supports at the corners). Next, I cut all the uprights - 6 angle brackets at the corners, and 5 pieces of 1 1/2" bar stock in between:

I welded the corner brackets on, then welded the top angle bracket cross-pieces on these. I did this so I could take actual measurements of the corner angle brackets and the rear bar:

After cutting the corner brackets, next step was to sand them all up nice and pretty (and cleaner for better welding). I used a cool flap-wheel sanding disk on my angle grinder - made short work of the rust, grease, and paint that was on the angle stock:

I then welded it all together...

...and ground off the tops of the weld beads where it mattered, and wire brushed the welding flux off of everything else:

Next challenge - the rear compartment. After removing all the carpet, it was clear that a minor rust problem was developing:

So, I used the flap-wheel disk and ground all the rusty spots down. One of the rusty spots actually penetrated - you can see the weld patch near the left rear whell-well and gas tank filler cover. Here it is, primed and ready for...

...cutting! I used a cutoff wheel on my angle grinder for most of the cuts, but some of the cuts were deeper (through non-necessary cross members). For those, it was Sawzall time:

Here is the completed hole. At the top, you can see the cross-members I needed to cut through. These were to support the gas tank, and are not needed for the electrical Jeep. They will provide extra sturdiness for the rear rack, though, so I won't remove them.

And here is the rear rack, dropped in to place! I had to enlarge the hole slightly (it's always easier to enlarge a hole than to make it smaller...) and had to bend up the sheet metal where the hatchback closing trim fits - it will get bent back once everything is mounted for good:

And here are 8 batteries test-fit in the box, all snug and happy:

Next steps for this rack: welding sheet metal around to make it waterproof; POR-15 and UV-resistant topcoat; seam-sealing; and final attachment. I also still need to fabricate the polypropylene top and steel hold-downs. Maybe next weekend... or I might work on the 7-battery upper rear rack next. Decisions, decisions.


Anonymous said...

Ross have you explored the idea of getting rid of the transmission altogether and bolting to the transfer case? I have driven my Cherokee in 4low and the max speed is about half that of 4High and the red line of the ICE is below the normal operating RPM of most electric motors. This would give more room under the hood by moving the e-motor to the position of the trans and eliminate more original weight. The weight of the trans has to equal a few batteries. Also the speedo drive is on the transfer case.
Mike F.
Kennesaw GA

Ross Cunniff said...

I thought briefly about eliminating the transmission and transfer case altogether; the spreadsheet which convinced me not to is here (the green boxes show where the motor HP is highest; the red boxes are past the 8K RPM motor limit). Note the extremely poor HP below 20 MPH for all but 1st and 2nd gear.

Based on experience with the Volt914, and based on this spreadsheet, I think the transmission has much positive value for the driving experience.

I have also toyed with replacing the 4WD transmission / xfer case with a 2WD transmission and front axle. But I could not find one readily available.

Anonymous said...

I understand a little better now. My Cherokee is an '03 automatic and the idea of converting to 2wd also crossed my mind. I was able to find a '89 2dr 2wd 5sp with a six cyl. The price was right at $200, but it has 230,000 miles and I beleave it had the weaker of the two models of transmissions offered by Jeep.
My interest in EV conversions came from my employer when they purchased a dozen Tiger Trucks. They are for off road use only because they are a from the factory conversion built in the U.S. on a Japanese truck platform made by Dihatsu. It is very small and only sold as a production ICE vehicle in Japan. Their range is short as an EV but they do serve a purpose in our huge facility.
I like my Cherokee and my drive to work is only 11 miles each way so the short range of an EV is okay with me. An EV conversion would serve me well as a second car.
What was your main reason for picking A/C over D/C?
Mike F.

Ross Cunniff said...

I chose AC because it is easy to get regenerative braking. Also, I am familiar with the DMOC440 AC controller from my volt914 project.

Yes, 11 miles each way is perfect for an EV commute. I expect that I will get 30-40 miles range from the Jeep, which allows for that kind of commute plus an errand or two.

Anonymous said...

Will you be installing an A/C system in the Jeep? I came across a conversion being performed on a BMW and they were using a self contained motor compressor unit made by a company called Masterflux. It looked like a fairly small unit about the same size as the electric MR2 steering pump.
The summers are pretty hot here in Georgia and with the short commute to work it would be ideal if it would leave enough voltage the drive.
Mike F.

Ross Cunniff said...

I do not plan to put an A/C in. In Colorado, I have the opposite problem :-) so I'm putting a heater in.

I don't see that A/C would impact your range enough that you would notice with just a "few mile" commute.