Managing Propller Thrust
 

Hello all,
I have just direct coupled the prop shaft to my motor which is a seaking 400 Size 3900kv Brushless motor.
Does anyone know if such motor can withstand the thrust from the prop, or should I install some kind of thrust bearing to protct the motor.
Thanks Geoff.

RE: Managing Propller Thrust
 

http://www.rcuniverse.com/gallery/ga...memid%3D504857
Photograph of set up here:
http://www.rcuniverse.com/gallery/ga...memid%3D504857

RE: Managing Propller Thrust
 

it should already have bearings pressed into the end caps/plates (where the shaft sits through)

RE: Managing Propller Thrust
 

Thanks Nic 30,
I expected that the motor design would provide the necessary thrust bearing to accomade thrust from the prop, but needed to check. Cheers and thanksGeoff.

RE: Managing Propller Thrust
 

looks like a Cen coupler..........

RE: Managing Propller Thrust
 

i've never seen a coupling like that

RE: Managing Propller Thrust
 

Geoff, the motor bearing isn't a thrust bearing (not designed for fore and aft pressure) and will prematurely wear out if you rely on it for thrust pressure. But on a prop drive you usually have a strut or stuffing tube/drive dog that will take up that force. Do you have a pic of the underside?

RE: Managing Propller Thrust
 

you should be just fine, give it a go and see what happens...

RE: Managing Propller Thrust
 

Thanks for the feed back guys. Here is a pic of the underside. In the build, I have only supported thestuffing tube with the strut. Itdoes not provide any resistance to thrust, so any prop thrust is transmitted to the motor. I was hoping that the bearing arrangement in the motor would support any thrust from the prop.
I got the universal from a hobby shop. And there is no coupling,The other component in the stuffing tube is a seal I made up to stop water entering the boat via the shaft.
ThanksGeoff.
Pic of the underside here: http://www.rcuniverse.com/gallery/ga...berID%3D504857

RE: Managing Propller Thrust
 

Geoff, it looks like the shaft is free to move back a few millimeters - stopping when the drive dog hits the stuffing tube. Is that right?

RE: Managing Propller Thrust
 

how about using a larger stuffing tube and putting in a couple of thrust bearings or get ones small enough to fit in the stuffing tube you have installed

it looks to me like the prop shaft can be moved more to meet the strut

RE: Managing Propller Thrust
 

Hi Sundogz and Nick30,
Yes, the shaft is free to move towards the strut, it is prevented from doing so by the position of the motor (or the length of the shaft). I could shorten the shaft to allow the drive dog to meet the strut. Or alternatively install a spacer on the shaft between the drive dog and the strut, forcing the strut to accept the thrust. Cheers Geoff.

RE: Managing Propller Thrust
 

Yes, or instead of a spacer use a thrust bearing. But then we're not talking about racing here, and a hard metal washer or maybe nylon/teflon would do fine. Then you don't have to worry about the motor's bearings taking all the lateral pressure from pushing the boat!

RE: Managing Propller Thrust
 

Thanks for the input guys, I have installed a spacer so I can get the boat on to the water and in the meanwhile will make up a thrust bearing. I recon that for a short run the spacer wont wear too much and the motor will be safe. Cheers Geoff

RE: Managing Propller Thrust
 

a little off subject but your water pick up seems to be extreme to me, mine only extends from the hull about an 1/8th inch and the rear of the tubing and the front is flush with the hull, seems like extra drag to me. i did some grinding to make it protrude even less then it does in this pic to the description i gave above, still get a nice consistent stream coming through the outlet

RE: Managing Propller Thrust
 

I was going to mention that myself but got sidetracked. Geoff, you should shorten it like Asupervee described or at least bend it towards the strut so the strut can protect it from hazards. You could lose the boat if you hit some fishing line or similar flotsam. [sm=surprised.gif]

RE: Managing Propller Thrust
 

Hi asuperv42 and sundogz,
thanks for the heads up on the water intake. I agree, I think i have been a little ambitious with the design. It will be a simple task to cut it back and prevent and consequential damage from hitting stuff in the water.
Thanks Geoff.

RE: Managing Propller Thrust
 

<div style="margin: 0in 0in 10pt"><span style="line-height: 115%; font-size: 8.5pt">Hey Guys, thanks for your assistance. We launched 'Baby Doll' today with all the necessary pomp and protocol. Baby Doll is a scaled down1930's design Italian speedboat. So we played the Italian National Anthem, Made some speeches as is the custom of launching vessels, poured some champagne over her bows. Then to the tune of Anchors Away, sent her to sea. The on board GPS recorded 10.2 knots. I know, I know, not a speed record, but she looked beautiful on her planning strakes. A too aggressive turn in the little wind waves resulted in an overturned boat in the water. No harm, Took the opportunity to check for any heat build up in the motor and ESC there was non, flipped her right side up and she was on her way again, until.... a sand bank got in the way, confirming the operator needs some training. Retrieved again. No harm, and with a little less aggressive running in the waves she again performed well.
Looking forward to the next day out when I will try a little more than half throttle and see what she will do for a top speed. Again than s for the assistance and advice. Cheers Geoff.</span></div>

RE: Managing Propller Thrust
 

Glad to help. She sure looks good under way! Yes, let us know how full throttle works out - I see the bow out of the water at this speed! Begood, Sdg.