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Brushless1
02-23-2011, 04:03 PM
All,

I am new to the website. Just registered today. Been doing FE boats for a while now and am expanding my horizons to learn more. Figure this is a great place to start.

I have two MRP fountains and am converting one to Brushless. I took the original drive system apart last night and want to keep the direct drive shaft. However, I do want to replace the prop and add a decent drive dog and shaft end cap. Here's my problem, the Shaft measures .138 in. Diameter. I am looking to find a decent Octura prop - maybe around 2 in pitch but none appear to be made for a 0.138 in dia. shaft. I know the MRP is way since defunct but is there a vendor that can supply a prop for this shaft? The motor will fit perfect with the curent shaft and coupler and all I'll need to get is a decent replacement rudder system.

BTW - I am using a 50A 2-7S ESC with a 2100Kv motor (8-18V). Figure I'll run a single 4S, 5,000mah battery to start with.

Fluid
02-23-2011, 05:45 PM
I am familiar with the old ABS Fountain with its submerged drive. It is large (42") but relatively lightweight - in its original configuration. What motor are you planning on using? Just stating the Kv does not tell us the power of the motor. For example, a 380 motor would be far too small for that hull. A 580 or larger motor is more appropriate, but what do you expect from the boat in terms of speed, run time, etc.?

A 50 amp ESC is way too small, particularly if you expect much speed from the boat. A 2100 kV motor is too high for a submerged drive and is almost certain to over-stress the ESC, and 4S is marginal power for this hull.

The MRP shafts were fitted with Octura plastic props as I recall, in a standard 1/8" (0.125") size. I wonder if a previous owner has replaced the original shaft with another? You will have a hard time finding any props to fit a 3.5mm shaft, better to replace the shaft with a 1/8" one.

Give us all the specifics possible and we'll try to help.




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Brushless1
02-23-2011, 08:39 PM
Excellent. Thanks for the reply.

Yes, its a 580 motor size. Motor can handle up to 18 Volts. I am looking for 25-30 MPH. I know the motor can handle it. The limiting factor is the ESC. its 50A continuous with burst to 60A. It can handle up to a single 7S. I figure a single 4S1P or even better (2) 2S1Ps 20C in series will be fine (up to 2,500 Mah). The Hull is Very light. Even lighter than the Proboat Brushless shockwave 26 that has a similar motor and ESC set-up.

Huh, so you say the shaft should be 0.125". I'll check again but my template says smaller than 4mm and fits within the 0.138 (or number 5) diameter hole. It makes sense for MRP back then because the standard thread for this site is 6-40 - Readily available nuts for the threaded end.

I didn't want to pull out the stuffing tube but I guess I will have too and replace with a 4mm. Just adds a bit more work and cost.

Thanks for the quick reply. If this set up works I will run in the MRP for a while and then replace with a NEU1700 Turnigy 120A marine and put this set up in a mini.