Alternator Pulley Project - Alignment - Helicycles.Orghelicycles.org/FOR SALE/Alternator Pulley Project - Alignment.pdf · pulley. This will allow the alternator and the drive pulley

AUTOMOTIVE ALTERNATOR CONVERSION FOR N750G PULLEY AND ALTERNATOR ALIGNMENT

Juan Rivera 19 September 2012 1

There are several different alignments that need to be considered and I’ll try to deal with them all here:

1) Static and Dynamic Balance and Alignment of the Modified Transmission Pulley 2) Static and Dynamic Balance and Alignment of the Alternator Drive Pulley 3) Alignment of the Alternator – fore and aft (it’s tight.)

Static and Dynamic Balance and Alignment of the Modified Transmission Pulley As you’ll see by reading the other files on this project, the transmission pulley fan tabs need to be machined off which removes quite a bit of material. It’s possible that this might alter the balance of the stock pulley, so the first question is, “was this pulley balanced at the factory?” I looked at two pulleys – one had a hole drilled in one fan tab suggesting that it was static balanced, and the other had no holes which mighty suggest that they realized that the stock pulleys were close enough not to require balance. Either way, the original balance might have been altered when the fan tabs were removed. I considered sending the pulley to be balanced but the cost seemed high so I opted to defer that decision. More on this later… Static and Dynamic Balance and Alignment of the Alternator Drive Pulley This pulley is fairly small and light in comparison to the transmission pulley and the quality is excellent, so I opted to defer the decision as to whether or not to balance this pulley till later as well. Installation and Vibration and Runout Testing for Both Pulleys The first step once the pulleys were installed on the transmission flange was to check radial runout.

In this picture the dial indicator is set to check radial runout on the alternator drive pulley. I started with the transmission pulley and found that the runout was ±.006 which is way more than I had expected. Both pulleys have clearance fit central holes that align the pulley so that the eight socket head cap screws (SHCS) are not used to align the pulleys – just to secure them into position. I rotated the transmission pulley in

one screw-hole increments, retightened the screws, and checked runout for each position.



The best was ±.004. After choosing that orientation I rotated the pulley until the side with the most runout was facing the dial indicator probe and then, using a piece of wood to protect the pulley, gave it a whack with a small hammer. That reduced the runout of the big pulley to ±.002, which is much better. I spot checked the drive pulley, torqued all eight screws, and then rechecked runout of both pulleys. They were both down to about ±.002 which I think is good enough. The next step was to reinstall the engine and run it up to flight RPM with the clutch engaged (no main rotor blades and no tail rotor drive shaft installed. I felt no change in the vibration of the frame of the transmission case from previous runs and holding my fingernail to the tail shaft and to the side of the alternator drive pulley proved to be smooth as silk. For now I’m satisfied with balance and vibration of both pulleys. I didn’t use any Loctite on the eight SHCS yet because they will be on and off a few times before I’m done. Before proceeding further I need to decide if the transmission moves excessively in relation to the frame during full power. The conventional wisdom is that the transmission moves at least ¼-inch at full power, but in relation to what? I’m only interested in what it does in relation to the part of the frame where I want to install my alternator mounting plate. I know the tail bends and twists and that affects the alignment of the tail rotor driveshaft, but that’s not a concern on this project. I’ve devised a simple test to measure the amount of movement and I’ll be doing that test tomorrow morning (11 August, 2012.)

I’ve written this up elsewhere so I’ll be brief – I installed a stiff cardboard piece that is attached to either side of the frame and stretches across from side to side. I cut out a center clearance hole for the transmission tail shaft and left four tabs in contact with the shaft. If the transmission moves in relation to this test piece it will grind or crush the tabs. I can then land and see exactly how much movement there actually was. If I have to I can do this again with a video camera pointing at this location, but I don’t think that will be

necessary. My plan is to hover the helicopter and do a few quick stops to put a good load on the rotor system and maximize transmission torque. We shall see… OK, now back to a top-level discussion of how these pulleys are supposed to align…



The project is based on the use of a commercial off the shelf racing alternator pulley that will mate with the alternator. Here’s a picture of the pulley:

This automotive racing pulley is machined from 6061 aluminum and hard coat anodized. During the installation and mounting of the alternator a jig and alignment plate will be used. The mating surface of the jig is designed to be exactly the same as the outer surface of this pulley, and the drive pulley is machined to match the cross section of this pulley. This will allow the alternator and the drive pulley to be aligned for perfect belt alignment.1

1 For now I’m assuming that the frame is stiff enough that transmission torque will not cause a large misalignment of the two pulleys when full power is applied. If I’m wrong I can either bias the alternator to bring it into alignment under power and account for increased belt tension, or I can scrap my current plan to mount the alternator to the frame and mount it to the transmission case instead. Tomorrow’s test will be critical!



Here’s a picture of the jig mounted on the alternator. The plate will mount to the jig using the four bolt holes you see on the front of the jig.

This side view shows the relationship between the alternator pulley in green, and the jig shown in blue. The alignment plate (pink) is shown bolted to the jig which screws onto the alternator shaft (gray.)



In this drawing you see the alignment plate attached to the alternator jig. The fat end of the plate will attach to the drive pulley using four long bolts or screws. The pulleys will be held in position against the mounting flange with the remaining four socket head cap screws. The shape of this plate is not important and the hole in the center could have a large slot to the left to allow it to be mounted with the tail rotor driveshaft in place. Any scrap will do as long as it is flat and rigid and big enough. Once I get to this part of the project I’ll add pictures of my installation. I plan to use a piece of 1/4-inch 6061 aluminum from my scrap bin2.

Here’s a look at the alternator mounted to the alignment fixture: I used a layer of masking tape between the pulley and the plate to prevent scratching.

2 Regardless of whether I use the frame or the transmission to mount the alternator, the jig and plate will be used to insure good alignment and help to hold the alternator in position while fabricating the mounts.



The alternator is now mounted in position using the spacer and a flat piece of .25 thich 6061 scrap. In this shot the alternator is rotated so that the two mounting locations at the top are inward and the tension arm mount is outside of the frame tube..

Here is a view with the alternator in a more upright position with the tension bracket mount inside the frame. This might be preferable because it would probably be easier to keep tension on the belt using something simple like a spring attached to the frame tube. (That’s what I ended up doing.)



If the alternator was to be mounted to the transmission, which would eliminate all of the alignment issues, a bracket could be attached using the bolts shown here. Fabricating a bracket to capture the rear alternator mount would be fairly simple since that mount lines up very well with the two left most bolt positions in this picture. The problem is that the belt tension is going to exert the most force at the pulley end of the alternator and there are no

mounting locations at that end of the transmission. For now this is too much work. I’ll press forward with the frame mounting. I’ll have to rethink the alignment scheme to account for the slight rearward movement of the drive pulley and the angular misalignment issue.

I biased the alignment plate with a piece of .063 sheet aluminum on the right side of the drive pulley to account for torque under load. This picture shows the location of the alternator so both pulleys will be in alignment under load.

The wooden stick is to hold the spacing I want between the alternator pulley and the frame tube, and to protect the powder coat. I also moved the mounts outside of the frame and behind the mounting plate.



I’ll make my two top alternator mounting brackets to place the pivot points half way between the frame tube and the mounting plate. I’m using a piece of polycarbonate for a

dummy plate so I can see what I’m doing. Once I get everything lined up I’ll use this as a template to fabricate the real mounting plate out of .25 thick 6061-T6 aluminum. This is the view looking aft. The fuel line is blocking the alternator’s connector. I’ll switch to a right angle AN fitting to clear the fuel line out of the way. Once I have the alternator mounted to the plate I can remove the alignment plate and install the alternator pulley and the belt. I have four lengths to play with. I want to use one that keeps the alternator clear of the mounting plate and the transmission pulley. Once I decide on the belt I can start on the tension arm.



Monday night, 20 August, 2012 – After work today I made the rear alternator mount and attached it to the dummy mounting plate. Now the alternator is secured in position and I can lay out the forward mount and fabricate that tomorrow. The mounting plate is angled in relation to the alternator shaft axis by about five degrees or so and I got that just right. With the mount secured to the dummy plate with two AN4 bolts I can still turn the large AN6 mounting bolt with my fingers so I know the mount is perfectly aligned with the alternator. Once I get that forward mount fabricated and installed I can remove the alignment plate and install the belt. When that’s done I can see just how far out of

alignment I am with no torque on the transmission. That will be a critical point in the project. If it doesn’t look too bad I’ll transfer all the holes in the dummy mounting plate to my 6061-T6 plate so I can run the engine up. I’m getting ahead of myself because I still need to design at least a temporary tensioning arm. But if all that goes reasonably well the next step would be to connect the wiring and do a test flight with the alternator generating power. I’ll probably install a video camera for that test. This should probably be in my other file called “Alternator Alignment and Mounting”. but I’ve come this far and I don’t have time to go back and move things around. Forward mount is now fabricated. It took me a while to get everything lined up since there are odd angles to consider. I ended up tweaking the footing side of my mount on the shaft end of the alternator in .2 degree increments until the pulley was exactly lined up the way I wanted. I did that with the other mount removed so the alternator would align itself solely based on that one mount. I did this after removing the mounting plate and attaching the alternator pulley. Then I used a stiff steel rod I had laying around as a straight edge. I dialed in the mount’s footing angle until the rod just touched the far end of the drive pulley. It cleared the near end by about .050, which is the distance I expect that side of the drive pulley to move when the transmission torques clockwise.



Here’s a view of the alternator mounted to the dummy mounting plate. To allow enough movement to take up belt tension I plan to use castellated nuts and cotter pins so I can adjust the tightness of the nuts just enough to secure the alternator but still allow it to rotate towards and away from the drive pulley. Disregard the shape of the dummy mounting plate. It will have a different shape. I cut away as much as I could on this one so I would have good access to reach around in back.



Here’s a view of both pulleys and the belt. I ended up with a 17 1/8” Gates belt from Napa Auto. The part number was 030265. In this picture you can see that there is plenty of clearance for the alternator pulley and you can also see where the tension adjustment arm mounting bolt hole is in relation to the frame tube. That will be the next challenge – Do I try to come up with an elastomeric tensioner, or a gas shock of some sort, or just lock it down in a slightly loose condition so it will have proper tension under load?



Friday, 14 August 2012 – Today I transferred my hole pattern and fabricated the quarter-inch thick 6061-T6 backing plate. You could lift the helicopter up by this plate. It’s not going anywhere. Notice that the axis of the plate is different from the alternator. It’s purely esthetics. It looks better to my eye if the plate is level when the helicopter is sitting on the skids. I could trim the back side of the plate to be parallel with the frame tube but I think this looks cleaner – again, just esthetics. It makes no difference. Now that I have a very solid mount I double-checked the alignment with the drive pulley and it’s exactly where I want it. It is slightly out of alignment now but should be perfect under load. It took several days of tweaking and adjusting washer spacing to get the alternator to be aligned exactly where I want it and free to pivot for belt tension. I have a workable idea now for a tensioner. There’s no doubt in my mind that it will work, but it will stick out about three inches and might be a minor hazard that you could stab yourself on. I’ll be tied up for the next two weeks with work, so I’ll have plenty of time to think about this last step before I wire it up and start testing with the engine running. This panel will have a hole in it so I can see my transmission oil pressure gauge and the remote sense 7-1/2 Amp circuit breaker will be installed there. When I’m completely done I’ll send all the aluminum parts out for black anodizing.



Here’s one last view of the final installation from the left side showing the transmission oil cooler at the top, the modified transmission pulley, the alternator drive pulley, and the alternator and its pulley.

Here’s a view of the back of the alternator showing the connector that attaches the ignition, idiot light, and remove sense wires. I swapped the straight AN fuel fitting I had for a right angle one to get the fuel breather line away from the connector and the vent holes for the regulator. I don’t want that fuel line next to a source of heat. The next step for me is to start on my electrical testing and also design and fabricate the tensioner. I’ll add another menu item for that project.



19 September, 2012 – Excuse all of my jumping around. Normally my entries are completely sequential but for this project I decided to make lots of topics. The result is that I jump from topic to topic. I’m not sure which is the best way. The installation is completed and I plan to do a flight test to check the tensioner to see how it acts when the transmission torques under load. It should maintain a constant belt tension and the spring should compress a quarter of an inch. I have video camera installed to capture that while I hover. I want to stress how tight the clearances are and how critical the alignment is – both angular and linear. The pulleys need to line up perfectly when the transmission is under load, so I preset the alternator so it’s slightly off on the ground but should be next to perfect in flight. That locks the fore/aft position. As it turns out, there is almost no room for the fuel breather on the lower right fuel tank. In the picture below I’m using a right angle AN fitting. I’m going to replace it with a 45º fitting to gain a bit of room.

This connector is on the back side of the alternator (facing forward on the ship.) This is actually ok, but it looks very close. I could always grind off some of that plastic on the connector since it serves no purpose. The alternator and the plug swing in a arc right past this fitting, but as I say, I plan to swap it out for a 45 degree fitting to open this clearance up slightly. Well, that’s it for this file. The flight test results will be in the mechanical test file.

Documents

Alternator Pulley Project - Alignment - Helicycles.Orghelicycles.org/FOR SALE/Alternator Pulley Project - Alignment.pdf · pulley. This will allow the alternator and the drive pulley