Adventure EV

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by on Dec.01, 2009, under EV Land Rover, Fabrication, Motor Bracket

I hope everyone had a great Thanksgiving!  I know I did.  No snow this year, but it’s getting cold around here nonetheless.  It makes working outside less than enjoyable.  We’re projected for a high of 28F on Thursday… so yay.  Well, I better get a lot done on Wednesday.

Starting the post out with a picture

It seems like it has been awhile since I last updated this blog with actual project material, but rest assured I’ve been toiling away.

One of the tricky bits has always been the connecting of the motor to the Land Rover’s transmission.  In some cases electric motors can be strong enough, have enough torque, to power the EV through a direct-drive link to the differential.  With my project, I decided I wanted to retain the transmission for a few reasons.

For one, I wanted to retain the full capabilities of the Land Rover.  That meant retaining the four-wheel drive system.  Sure, it’s not the most efficient way to go, but keeping the Rover’s full off-road capability was one of my design mandates, and the easiest way to accomplish this was to utilize the existing transmission.

Secondly, the transmission allows me to change gear ratios in order to improve performance and efficiency.  The Land Rover isn’t the lightest conversion, so being able to downshift to climb a steep hill could help.  My projections indicate that I’ll be able to do most, if not all, of my driving in third gear up to 60mph.  Past 60mph I’ll need to grab fourth.  We’ll see if I have enough torque to start off comfortably in third.

Electric motors like to spin, they’re not happy poking around, so while I may have enough torque and power to single gear most of my driving, it may not be the most efficient at slower speeds and higher loads.  Again, the gearbox gives me flexibility.

Thirdly, the transmission’s clutch becomes a safety device.  In the event of a motor or controller failure which might result in the equivalent of a full-throttle situation I can easily disconnect the drive through the clutch.  Let’s hope this doesn’t happen.

Lastly, it’s just easier.  Connecting to an existing transmission is a common conversion technique, so many components already exist to facilitate this… like my adapter plate.

Motor with adapter plate.  Flywheel and clutch mounted.

I once considered going with a direct drive AC system designed to haul electric buses around, but in the end I didn’t like the performance specs, and while that system (Azure Dynamics’ AC-55) was designed to connect directly to a rear differential via a driveshaft and yolk, I would have needed to engineer a way of connecting it to my transfer case if I wanted to retain four-wheel drive.

You may have heard that a good conversion means lightweight and no four-wheel drive, two rules I’m somewhat breaking.  Maybe more like bending.  The Land Rover, as we’ve discovered isn’t terribly heavy for what it is.  I’ll keep telling myself that.  And the four-wheel drive system is unlike most modern setups.

The Rover’s four-wheel drive system is actually very basic.  It’s a manually selectable, part time four-wheel drive system.  That means most of the time I’m only in rear-wheel drive, with the front driveshafts disconnected by freewheeling hubs.  While there are still an additional set of gears to run through in the transfer case, it also means that there are no frictional losses running the front driveshafts and wheels when I’m in two-wheel drive mode, as you would find in most modern drivetrains.  Not so bad.  During the occasions I would need four-wheel drive, I shove down a lever and I’m in locked four-wheel drive.  True, I still have to lug around the weight of the additional four-wheel drive components, but that’s the way it is…  otherwise I would have converted something like a Civic.

Anyway, back on target.  While waiting for some additional components needed to mount the motor to the transmission, I test fitted the motor temporarily.  I needed to solve how I was going to mount the motor to the chassis.  The motor and transmission, when coupled together, act as one big unit, but the transmission’s mounts really only serve the rear of the unit.  The motor needs to have a front mount.

Here’s what I saw with the unit bolted together:

Conundrum_v01

The yellow circles are the two existing motor mounts.  The red arrow is pointing out the only position I can wrap my motor mount bracket around.  Big difference in location.  That flat black plate is the bottom of the motor mount bracket.

Mounting the very back of the motor would have been perfect, but that’s not a very structural part, and it’s where all the motor cooling happens with a fan back there.  Further forward and I run into a band of metal that covers the internal brushes, that’s a no go.  Further still and I hit the electrical connection block, that’s out.  So just in front of the block it is, then.

I have two options here, try and build some kind of bracketry to connect everything up, but I don’t like the idea of being levered out that far away from the chassis mounts… or build new mounting points into the chassis.  The latter idea isn’t attractive as it would mean designing new brackets and welding them to the chassis, but it’s the idea that won out in the end.

First I built a template out of cardboard and determined where on the frame I wanted the new mounts to go.  I soon discovered that I wouldn’t be able to put the new brackets directly under the mounting band because of front driveshaft clearance, so the mounts go a few inches to the side.

Template

The brackets are made from 2″x3″ – 1/8″ rectangular steel stock.  Initially, I wondered if the 1/8″ wall material would be strong enough, but the existing chassis used 1/8″ material that supported 490 lbs of engine and accessories instead of the motor’s 200 lbs.  Weight won’t be the issue, hopefully the increased torque from the electric motor won’t be, either.

After tracing the arc designed to allow driveshaft clearance on the steel stock, I used an angle-grinder and cut-off wheel to transfer the shape.  Came out kind of nice,  a relief after shattering a half dozen cut-off wheels with previous tasks.  Cut-off wheels are tricky, a slight grab or cut to deeply at the wrong angle, and they just blow apart.

Cutout

A smaller bracket was fabricated for the other side.  Both brackets have open bottoms to prevent them from collecting and holding debris.  Once welded to the frame, they should be very strong.

I decided to keep the existing mounts, in case.  In case of what?  I don’t know… returning the vehicle back to stock?  Doesn’t seem likely, but the stock mounts aren’t in the way, so for now they stay.

Here’s the longer bracket next to the stock bracket… you can see the driveshaft below it.  While nowhere near the bracket now, when the front axle is under articulation off-road, the driveshaft would have hit the new bracket if it had no arch.

Detail

Here are the two brackets welded into place, and you can see the arch in the original mount, as well.

New Mounts In Place

I’ve painted the brackets with POR-15, which works brilliantly for this stuff.  I coated the frame with POR-15 awhile back and the paint is tenacious!  You can’t scrape it off with a screwdriver.  Only an angle-grinder has succeeded in removing POR-15 from the well prepped chassis.

Hopefully, by the end of tomorrow you should see the painted result with the motor in place and mounted!


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3 Comments for this entry

  • mikefish

    Hey man! Looking at the new motor mount, and it looks a bit thin. Do you think that will be enough to handle all the torque of the electric motor? As you know, the electric will have instant torque, and the old ICE engine was not as abrupt on the torque. Do you plan to place more mounts on the electric motor, or just the two new ones you are making?

  • jeffg

    I’ll just have to see what happens with these new motor mounts. I figure, if they do fail it will be in one of two ways…

    Either the mount will shear off completely due to my welding (in)comptence, or the mount will bend. The only real way the mount could bend is if the bottom open edge splayed out enough to reduce the vertical shear strength of the box section. If you look closely you can see a weld on the bottom side of the arch. That’s a 1-1/2″ strip that was designed to hold the open bottom together, so it’s still kind of boxed.

    You’re right, though… if it fails it will probably be due to torque. I’m retaining the original rubber mounts, so that will help soften the torque transfer, and there’s still the transmission and the rear mounts doing half the work, as well.

    At some point I’ll have to limit instantaneous torque anyway to save the transmission and axles themselves.

    Only testing will confirm…

  • mikefish

    I did miss the extra welded piece underneath. If possible, I would try to place one inside, kinda like “ribs” to give structural support inside the shape as well to help prevent sheering. If that is not possible, then like you said, I guess testing will tell! 😉

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