DPV Construction Begun

[Larry Horne]

Wiring

Will,

If you go to the 12-30-05 post, I show (maybe not as well as I can) the back portion of the trolling motor. I only bought the motor lower unit. Using a hack saw, I cut the round end off of the housing (where the brush set is mounted) and also cut off the threaded nipple where the unit's mast tube would be fitted. I filled in all holes with JB Weld.

I then tapped the brush housing threads out the back of the unit so that I can make a plate and gasket for it. I will run the two wires through the plate and epoxy in place. I will then bolt the gaske and cover in place with maybe a little sealent.

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I've attached a few pictures of the rear portion of the lower unit assembly. As you can see I cut everything off of it that is not needed and filled in the hole where the nipple was for the mast with JB Weld. Once I had the end cut off as in the second picture I placed the piece on a belt sander and sanded smooth. i was able to see where the piece was tapped to accept the small screws for the brush assembly. I used a dremel to hand machine the back to locate where the threads would come out and then drilled into the exiting holes but from the side I cut and sanded. I then ran the appropriately sized tap from the inside out through the new holes on the rear. What this did is allows me to use the same threads that hold the brush set in place to now hold an end plate and gasket in place.

The 4th, 5th and 6th attached photos show how I modified the rear section (brush set housing) of the motor and eliminated the mast, skeg and end portions. Now I simply make a plate and gasket. Drill the plate with the two holes for the electrical leads and there you have it.

Now I will insert the motor from the inside of the motor tube/motot housing and use 3 1/8" cross section diameter o-rings to seal between the trolling motor and the fiberglass motor housing. The piece in the 1st photo. To secute the trolling motor to the DPV I plan to use the two holes in the end of the motor housing (the ones I tapped) to also bolt on an aluminum bar (1" wide and 6" long) which will be bolted to the DPV end section. (I will embed two 1/4-20 SS nut assemblies in the fiberglass).

I have this all in my plans but am not there yet on the fabrication.

Give me a couple of days to move forward. I just ground a hole in the fiberglass (FG) body that I am repairing so another day on it.

Sorry, confusing but I will get you photos next.

I will mock it up tomorrow night and take a shot or two. I plan to insert the trolling motor into the motor housing I am fabricating. View attachment 27895 as described above. Stay tuned.

Lar

 

[Tavi]

I've got one of those trolling motors thats been just taking up room in my basement!!
I'll be watching the rest of this thread!!

 

[willydiver]

Lar,
Thanks for the explanation. I used a Motorguide trolling motor for my MkI, which has a different internal setup. On the Motorguide, the brush plate is on the aft end just before the shaft exits the casing. The fore end cap of the Motorguide has the front shaft bushing pressed into it, so it's not easy to do without it or modify it. It looks like the setup of the MinnKota brand is more friendly for use in a scooter. I like the way the front thrust bearing in the MinnKota is incorporated into the brush plate and the wires are located in front of any spinning internal components.

What do you suppose is the funtion/purpose of the wires being potted (sealed) in the front of the MinnKota nose cone?

Thanks,
Will

 

[Larry Horne]

I'm told that the stuff in the epoxy is for the variable speed function.

Actually, the company I bought the lower unit for sells them to a R&D company that uses the 40# units in their DOD submersibles so I knew the Minn Kota was the way to go. They have run them to 300 ft un-modified.

OK

I took this evening to do some photograph of how I plan to integrate the motor.

Here you go:

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These show the brush housing, the tapped holes and the end plate mocked up and then installed in the motor housing tube which is installed in the units end unit.

Thoughts?

Lar

 

[willydiver]

Lar,
Those pics are very helpful in visualizing the setup. Just a couple of thoughts, though. The rotational torque resulting from the prop turning in water will be pretty substantial. Make sure the motor is bolted at it's attachment points sufficiently to handle this force.

Also, I see the oring on the body of the motor and how it will seal the annular space between the motor body and motor tube. But how will the oring be secured to prevent it from being pushed into the tube/motor assembly from water pressure?

Also, can you give any contact info/prices for your motor supplier?

Looks great!

Thanks,
Will

 

[Larry Horne]

Will,

I've been thinking. Another way to seal the stern of the motor would be to JB Weld a flat aluminum disk in place and then drill and seal the two openings for the power leads.

As for keeping the o-rings from pushing in............I planned to use a flexible sealant I found at the local Bass Pro Shop this weekend called Life Caulk..............

http://www.jamestowndistributors.com/find;a;1;ID;,Caulking,Boatlife,Life.Calk

As for the motor's rotational torque, the plan is to have the force held back by the shape of the area where the aluminum bar will seat, not the 1/4-20's.

As for the motor vendor, its a local trolling motor repair shop. $125 new.

Lar

 

[willydiver]

Alright Lar, give us an update.....

What type of handles/config. do you propose to put on the DPV?

Thanks!
Will

 

[Larry Horne]

Ok Will

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Progress is slow but moving forward.

I have posted pictures shoing how I am modifying the "stern buldhead" to receive 2 1/4-20 SS bolts which will hold the motor in place. I am having a piece of 1/8" thick AL plate cut into shape. Its a circle the diameter of the end of the trolling motor with two 1" wide "ears" coming of at 180 degrees of each other. Pic coming once done. I will use this to bolt to the rear of the trolling motor and then the motor to the "stern bulkhead". The buldhead needs to have straight in access for a 7/16" scoket so the bottom 2 pics show how I carved out the foam and used a circlar form (paper towel tube wrapped with metal ducting tape and sprayed with silicon to release) to hold the shape while the syntactic foam (GREAT STUFF trade name) hardends. I will do the same on the 10" dia piece that mates to this and inserts into the main tube. I will then fiberglass over it all to make it nice looking.

NOTE: NEVER NEVER NEVER *****ING EVER use DAP water based foam. Its CRAP. I cannot go on enough how crappy this product is. USE GREAT STUFF, its the best for all applications.

OK the other photos show the foam being applied to to the main tube that I will later fair into the tube's body giving me a nice transition from 10" to 12" dia. I have embedded the AL blocks into the main tube for mounting the "J" end of the SS draw latches. I need to lacate larger draw latches but so far not so lucky. All of my internet searching comes up short. I have 6 now, but I think they are too small for the weight I am expecting. The Apollo AV-1 has 4 nice ones but Apollo wants $22 each..........blow me.

The other shot is of the battery tray starting to come together. It's 3/32" plywood that I will fiberglass later.

OK..........now I need help. I just spoke with MINN KOTA tech support regarding the specs for a 2004 Enduro 55# trust motor:

55# trust
average RPM = 1400
45 Amp draw at full speed
tested to 2 atm


Question they will not answer: How wet does the motor housing have to stay in order to disapate heat? My motor tube housing is designed to come to the end of the motor's housing................thereby leaving a 1/8" air gap completely around the motor. If it gets hot it could damage the buna N o-rings I am using for sealing or simply burn out the motor..........I was designing it this way to solve my "seal the original motor housing differently" issue for pressure at 130 ft..............

Gotta do some more research on this part.

As for the handles, I am thinking of something like the MAKO with two on the shroud and a tow harness. I may do a T handle also, just would have to use two reed switches where either one would throw the relay.

I am also going to build a single battery housing for boat use. I have done some initial calculations and I think I am currently to bouyant. I may have to loose the rounded front end of the two battery housing...........if not I will need a jib crane to load it.

End

 

[willydiver]

Looking good Lar. The cooling of the motor (when the design excludes it from water contact) has been a problem I've been trying to solve, also. The motor will get hot with continuous use for sure. I've thought of connecting some form of a "heat sink" to the motor casing and exposing it to the outside water. Aluminum would be a good choice of material to make this out of. Only problem is the sink needs to contact the motor casing in several places to conduct the heat away evenly. And then you create another sealing problem when you do this. One method may be to just leave a portion of the motor casing outside of the housing so it's exposed to the water. That should be enough to draw excess heat out. If you think of the commercial brands, like Apollo, their motors are completely contained within the scooter body. Those motors are likely not contained in a steel housing like the trolling motors and open to the atmosphere within the housing. Even so, the air inside the Apollo's housing would heat up during continuous use. But there don't seem to be any problems with them overheating. Perhaps some holes could be drilled into the trolling motor housing (in appropriate places) to allow the heated air to circulate out of the motor and into the housing. Perhaps the heated air will conduct its excess heat energy through the housing body to the outside water.

Will

 

[Larry Horne]

Will,

I'm ahead of you. Wednesday night I shortened the motor tube so that 2/3 of the trolling motor's housing was exposed to the water. I "attempted" to modify the internals of the fiberglass motor tube to allow for a seating surface between the end cap (green piece in pixs) and the fiberglass tube. I was going to place an o-ring in there because there is a step up or diameter difference between the trolling motor's steel housing and this end cap. FYI the "professionals here at my company" used MINN KOTA trolling motors that had the brush sets on the same side as the output shalf. This allowed them to insert the motor into a machined tube and seat the butt end into the machined tube with an o-ring between it and the submersible. They then bolt thru the housing and directly into the trolling motor housing, using the bolts themselves as conductors. I'll sketch it for you and send it via PM.

But my lesson 1. I used poster board to form a dam around the trolling motor casing and inserted the motor into my fiberglass tube (after I trimmed it to allow the motor to get rid of heat). I wiped the motor with silicon and covered the poster board with aluminum tape to serve as release. I used an o-ring to complete the bottom of the dam. I was attempting to improve the internal ledge in the fiberglass tube so that an o-ring would seat well. The resin leaked past the tape and saturated the poster board. Bonding the trolling motor to the fiberglass tube. I had to completely cut the tube along its longitudinal to separate the pieces. Now I have a lot of hand work to smooth the interior and fix the cut.

Lesson 2. Tiger Hair filler will desolve Great Stuff foam................you figure out the rest of this one........

Off to DC for the weekend so no work until Monday night.

Lar