Motor Mount for the Doka, Part 2

We cut and mitered the final section of square tubing for the motor mount, and bolted the full assembly to the frame rails.  We discovered that the rails ware not rigid enough for this design.  There was quite a bit of flex at the back end of the motor.  Fortunately, the solution wasn't too bad.

A vertical section of square tube was welded to the motor mount arm, and bolted to the frame rail.  Attaching in two places, at 90 degrees was a big improvement.  The effective length of the arm that is cantilevered out to the motor is shortened substantially, and the load is spread across more of the frame rail. 

Here is another view from underneath:

The view from the back isn't too bad either.

Once we get a coat of paint on that bare metal, it is going to look like the motor mount was original to the vehicle.

Sprite Battery - Rear Rack

These are the same cells that are used in the Nissan Leaf.  Each module has 4 cells, wired 2 in series and 2 in parallel.  The voltage of each module is 7.5 Volts, with a capacity of 65 Amp-hours.  We have 48 modules available, provided we can find enough space in the car to fit them.
 

20 modules will fit in a rack behind the seats.  Ideally we will be able to locate the rest of the cells in the front of the vehicle, under the hood, the maintain a decent weight distribution.

The Sprite Motor and Transmission Become One

In today’s episode we take the adapter plate that we made in this blog post and the hub that we made in this post to join the motor with the transmission.  Here is the drive end of the electric motor.  Just inside the ring of 24 tapped holes, there is a lip.  This lip is used to align the motor to what ever you are bolting to the motor.  We won't need all of the tapped holes.  Those holes represent a lot of mounting options.

We didn't make the groove in the adapter big enough to fit on the lip of the motor.  It took a bit of hand filing to get the adapter to seat properly.  In this case a bit is around 2 hours (at least it felt like two hours - might have been 45 minutes - I'm not sure because I've blocked it in my brain).  You can see that we are only using 6 of the available 24 tapped holes.  But don't install the bolts just yet.

The round adapter is not big enough to for the transmission bell housing, so we have this 12" x 24" x 0.5" (300 mm x 600 mm x 13 mm) plate that gets stacked on top of the round plate.  We took care center up all of the plates, and use 1/4" (6 mm) pins so that the motor and transmission shafts are aligned.  Error here will cause vibration and excessive wear or failure.  Total error is on the order of 0.003" (75 microns).  We made a collar that held the shafts aligned, and used transfer punches to mark where the transmission bolt holes and alignment pins should be located.  These are the holes in the irregular pattern around the outer edges of the plate.  Now is a good time to install the 6 motor bolts. 

 Looks good so far.

 Next, the hub is installed on the motor shaft.  That small hole on the hub had to be drilled and tapped to a larger size than the other three.  The flywheel was mounted on the old gas engine crank shaft with two different sizes of bolts, so that the flywheel only bolts on in one orientation.

 The flywheel gets bolted to the hub.  The lower right bolt is slightly bigger than the other three bolts.  The flywheel has three jobs with a gas motor - provide mass to smooth out rotational pulses from the explosions of the internal combustion cycle, provide a way for the starter motor to couple to the crank shaft and get the engine started (see the gear teeth around the circumference of the flywheel?), and it provides a surface for the clutch disk to grip.  Electric motors deliver smooth power and can start up on their own, so we only need it for the clutch disk.

 The pressure plate also has a surface to grip the other side of the clutch disk.  It has a bunch of springs and a mechanism to release the clutch disk pressure when you press the clutch pedal.

 Now we slide the transmission and motor together, and on the second attempt, everything fit together as we expected the first time.  It turns out we didn't drill the center hole in the hub deep enough for the length of the transmission shaft.   But after scratching our heads for a while, we got it all figured out.

This motor and transmission need to end up in that Sprite.  Easier said than done...

 

You just tip the nose of the transmission down, and slide the engine hoist that way, and rotate the motor to clear the hood latch.  It doesn't help that the engine hoist base is too wide to slide between the front wheels (or the Sprite is too narrow).  Something is not quite fitting correctly.  Time for some more head scratching.

We quickly identified the issue.  The lower corners of the adapter plate are hitting the frame rails of the car.  It's nothing that can't be solved with a little time with the saws-all (reciprocating saw).

 That looks really good.  Like it was meant to be.

The gear selector lines up exactly where it is supposed to go.

Machining a Hub for the Sprite Motor

With the recent transition to daylight savings time and the longer spring days ahead, I can't say that I will miss working under the tent in the night and rain.  Warmer weather is around the corner.

We focus some of our attention on the Austin Healy Sprite.  We need a way to mount the flywheel to the Remy HVH 250 motor with a 25 tooth , 25 mm (1") diameter splined shaft.

We have a  coupler that has the correct splines to mate with the motor, but it is not big enough to mount to the flywheel.  A big chuck of 1018 steel will be turned to go between the coupler and flywheel.

We begin with a big cut.  This big band saw was perfect for the job.  Don't try this with a hack saw:

35 minutes later, the blank was ready to be mounted in the 4-jaw chuck on my lathe.

After a facing cut, blue Dykem really helps the scribed layout lines to stand out, especially when the work is spinning at 500 rpm.

Several hours later, removing 0.015" (380 um) of material per pass with the lathe, producing a big pile of  metal chips, the part is complete.

To join the coupler and hub, we settled on using an interference fit.  An interference fit involves making the bore smaller than the cylinder.  The resulting friction yields an extremely strong connection.


To get the bore diameter correct on the hub, I made a plug out of aluminum that is 0.004" (100 um) smaller than the spline coupler.  The bore in the hub is carefully opened up until the aluminum plug makes a slip fit in the bore.  The resulting interference between the coupler and the bore should be about 0.003" (75 um).

Absent a ginormous hydraulic press, the hub was heated up to take advantage of thermal expansion to increase the diameter of the bore.  This is Paul's oven.  We were going to use my oven, but it caught on fire earlier in the evening while my wife was cooking dinner.

The spline coupler was placed in a bowl of dry ice to shrink the diameter.

After 45 minutes of soak time, we joined the two parts.


In an ideal case, the coupler would have just dropped easily into the hub, and parts would bond as the temperature difference closed.  In reality, the interference was a bit too much - aiming for 0.002" (50 um) would have been better than our 0.003" (75 um).  The hub dropped into the bore about 1/3 of the way, and stopped.  Brief panic ensued, but we did plan for this possibility.  Paul grabbed the emergency hammer and fully seated the coupler into the bore.

The flywheel is now mounted to the motor.  Success.

Motor Mount for the Doka

It is time to fit the motor and transmission into the Doka.  If we had a transmission jack, sliding the assembly under the rear bumper might have been easy.  We have an engine hoist, so through the engine access hatch we will go.

It almost fits.  We just need a few more inches of clearance. 

We used a floor jack to lift the rear bumper a couple of inches and the motor is positioned snugly into its new home. 

The mount on the nose of the transmission will remain stock, but the engine mounts will not work for the electric motor.  We will re-use the mounting holes in the frame of the Doka, but we need to fabricate a new steel structure.


Here we are laying out the miter angles for a few cuts.

And we arrive at this shape, a cradle of sorts, to attach to the bottom of the electric motor.  The goals of the design were to use a pair of Volkswagen motor mounts to minimize drive train noise and shock from transferring to the frame, and to maintain as much ground clearance as possible. 

Next we need a pair of ears to stick out from the frame rails, to support the cradle arms from below.  To make a proper fit with the motor mounts, we need to thin the ends of our 1.5" (38 mm) square tube down to 1 inch (25 mm).  We used a grinder to section out 0.5" (12.7 mm) of material, squeeze it in the vise, and weld the material back together.

Some day I will remember that welded and freshly ground upon material is quite hot.  Here the motor mount arm is enjoying a mild spring day, cooling to a more manageable temperature.

After a bit of grinding, the arm looks quite good, and more importantly, it fits the motor mount isolator.

And here is the competed motor mount assembly, ready to be attached to the vehicle.

Joining the Motor and Transmission, Part 3

We last left off with bolt trouble, while trying to join the Doka transmission and motor.  The difficulty was in determining the correct size of bolts to use.  Bolts are specified by diameter and the thread pitch (and length and material and grade and head type and... the list goes on).  The diameter of our tapped holes for mounting the flywheel looked like they could be either 7/16", M12, or 1/2" (all within 60 thousandths or 1.5 mm of each other).  7/16" had the right thread pitch, but was a rattle fit.  1/2" was just a bit too big.  The thread pitch of the 7/16" bolt was the imperial 20 threads per inch, within 1.5% of the metric thread pitch of 1.25 mm per thread.  There is an M10 bolt with 1.25 mm pitch, but the fine threaded M12 bolt is 1.5 mm.  Nothing seemed to make sense until we found out they make metric bolts in extra fine pitch.  Of course they do.  Our solution was an M12 bolt with 1.25 mm pitch.

Here is the face of the motor fitted with the hub and adapter plate.

After bolting on the flywheel, the clutch disk is centered using a nice alignment tool. Do not even attempt to replace a clutch disk without an alignment tool. The transmission and motor need to line up at the same time that the transmission input shaft lines up with the splines in the center of the clutch disk.  Once the pressure plate is bolted on, the clutch disk will be fixed, and the clutch alignment tool is the best way to ensure that the disk is centered.

Now that the pressure plate is bolted to the flywheel, the alignment tool can be removed - the clutch disk is secured and centered.

After all of that, it really is as simple as bolting two halves together.

Machining the Sprite Adapter

Warning!!! Innocent carbide tooling was harmed in the making of this adapter plate. Viewer discretion is advised.

We turn our attention to the Sprite, and the most challenging part of the conversion: machining the adapter plate. See this post for more information on adapter plate function and purpose.

This is a 12" X12" X 1.5" (300 mm x 300 mm x 38 mm) chunk of 6061 aluminum. 

This is the Remy 250 HVH that will power the Sprite.

There are two important features that we need to design into the adapter plate: a bolt circle of tapped holes with diameter 8.46" (215 mm) and a raised lip with a diameter of 7.09" (180 mm). These features are concentric with the motor shaft, where tolerance in positioning is critical.  Any error will cause misalignment between the motor shaft and the transmission shaft, with possible vibration, excessive wear, or malfunction.

There are other features that do not need to be located with high accuracy: A 4 inch (100 mm) clearance hole for the motor shaft and hub, and a nice round perimeter is nice aesthetically and sheds some weight.

The first step is to rough out the shape.  This was first attempted on the band saw.  Based on the rate of cut we decided to speed up the process and used a table saw with a carbide tipped, high tooth count blade.  This faster method only took a couple of hours.  Probably none too soon for Paul, who was getting hit in the arms with hot aluminum chips, while feeding a hot and sharp edged part into the blade.

 Only 8 more cuts to go, Paul!

Here is a 16 sided polygon, in the rough shape of our desired circle.

We had two options to finish the part: milling machine or lathe.  The lathe can clean up the outer perimeter of the adapter, and cut the groove for the motor face lip in short order.  With a rotary table on the mill, we can easily locate six evenly spaced bolt through holes on an 8.46" (215 mm) diameter.  The mill can clean up the outer edge and cut the groove, but not as quickly or nearly as cleanly as the lathe.  Because the features need to be concentrically located, being able to do all three operations with the same set up made the mill the clear choice for us.

We made and installed a collar on the center axis of our part.

 Now the part is aligned to the center of rotation of the rotary table.

Taking 0.050" (1.27 mm) depth of cut with each rotation of the table, we were able to make an attractive disk in a mere 30 passes.  Only 10 more to go, Paul.

Next we turned our attention to the groove.  This feature needed to be about 0.125" (3.2 mm) wide and deep.

 

Disaster struck as our fairly expensive carbide end mill suffered an unfortunate fate.  And we thought we were taking "light" passes.  We shall never speak of this incident again.

This step was really satisfying.  This was the first time I have had the luxury to use a rotary table to lay-out a bolt circle, and I must say it is far superior (faster and more accurate) to using a divider, center punch, and drill press.  All you do is move the X axis of the mill to the correct radius for the bolt circle, as displayed on the DRO (did I mention this mill also had a digital read out), and rotate the rotary table in 60 degree steps for each hole.  Here we are "spotting" the drill locations with a stout center drill.  This maintains the correct location of each hole, because twist drills tend to walk on you, if you try to start them on a flat surface.

The final drilling operation was uneventful.  

We are left with a pile of aluminum chips to clean up, and a part that we can be proud to say we made ourselves.