# More Cost Efficient Trolling Motor DIY

#### baucat9

Joined Oct 27, 2014
28
Hello AAC. I have been trying to get this thread out for a while now. I have a couple thrust questions in relation to a trolling motor i am designing to work with a smaller, more cost efficient battery opposed to a Marine Deep Cycle. With new technologies in the electric motor world, it is easier than ever to get large amounts of torque out of a motor that does not use that much power. My design consists of a 12v motor with a drive shaft going down to a 90 Degree gear box that connects straight to the prop shaft. Im looking for around 3000 RPMs in a motor. The math says a majority of motors that can produce this kind of RPMs will be able to push my little 200lb boat at a decent pace. Now I'm coming hear to hear a few suggestions on parts. Any decent size 12v motor with an RPM rating of 3000 will work for this project. If anyone has done a similar project and has a product/brand recommendation that would be great. Next is the 90 degree gear box. I have seen someone with a similar project take on out of an old grinder that has a 3:1 ratio. This is where i need a little help. I know these are a little pricey, but i want a good quality box that doesn't break the wallet. Lately and arguably the most difficult part of this project is the battery. I want the motor to last approximately 1.5-2 straight hours of operation. Something light and cost efficient would be ideal. All Help is greatly appreciated!

#### #12

Joined Nov 30, 2010
18,223
I have a couple thrust questions in relation to a trolling motor i am designing
Any decent size 12v motor with an RPM rating of 3000 will work for this project. If anyone has done a similar project and has a product/brand recommendation that would be great.
YOU are designing a motor and you want somebody to recommend which motor to buy?
That part seems contradictory.
Then you want somebody to define a, "decent pace", calculate the horsepower required, the battery required, and do it all for cheap.
What part of the designing are YOU doing?
And how does the battery make an off-the-shelf motor and a right angle gear box more efficient?

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#### Alec_t

Joined Sep 17, 2013
12,249
With new technologies in the electric motor world, it is easier than ever to get large amounts of torque out of a motor that does not use that much power.
Certainly newer motors can be more efficient than older ones, but to provide the thrust needed to move your boat at a given speed will take the same mechanical power, regardless of which motor you use. Let's suppose your 'new' motor has an efficiency of 95%, whereas an 'old' motor has an efficiency of 80%. With the 'new' motor the battery charge will last 15% longer: but you are still going to need a marine deep cycle battery IMO .
As for using a gearbox from a grinder or similar, that would have to be re-engineered to include waterproof bearings/seals. Do you have the facilities for that? It is doubtful, too, whether it would withstand the propellor torque needed.
The math says a majority of motors that can produce this kind of RPMs will be able to push my little 200lb boat at a decent pace.
I suggest you re-do the maths. A tiny 12V model motor can certainly do >>3000rpm, but wouldn't have the necessary torque at that speed. You need to calculate thrust x speed to get the power to move the boat, then factor in motor and transmission efficiencies to get the motor power needed. Knowing that, and how long the motor must run for, you can work out the battery capacity needed. It won't be as small as you'd like.

#### baucat9

Joined Oct 27, 2014
28
YOU are designing a motor and you want somebody to recommend which motor to buy?
That part seems contradictory.
Then you want somebody to define a, "decent pace", calculate the horsepower required, the battery required, and do it all for cheap.
What part of the designing are YOU doing?
And how does the battery make an off-the-shelf motor and a right angle gear box more efficient?
I have an idea of what i would like to use, but since most of these sites are made in China, I was checking to see if anyone had done a similar project and they recommend a brand or model. I have all of this completely figured out upon what i would like to do. I am no where close to an expert, so I was seeing if someone who was might have a few suggestions. Thats all. I am not looking to make the motor more efficient in terms of running, i mean in terms of cost. I was typing this thread on a mobile device, so i didn't have my computer with all my calculations to post them. I have the horsepower figured out a well as what battery to use. I was just going to check with AAC to see what you guys think, so i do not have to spend a lot of money researching the right battery and motor combination.

#### Papabravo

Joined Feb 24, 2006
16,955
I have an idea of what i would like to use, but since most of these sites are made in China, I was checking to see if anyone had done a similar project and they recommend a brand or model. I have all of this completely figured out upon what i would like to do. I am no where close to an expert, so I was seeing if someone who was might have a few suggestions. Thats all. I am not looking to make the motor more efficient in terms of running, i mean in terms of cost. I was typing this thread on a mobile device, so i didn't have my computer with all my calculations to post them. I have the horsepower figured out a well as what battery to use. I was just going to check with AAC to see what you guys think, so i do not have to spend a lot of money researching the right battery and motor combination.
I don't know if I would have any confidence in mechanical parts purchased from China. What happens if you get something you are not happy with? What is their customer service like? AFAIK you're on your own.

#### tcmtech

Joined Nov 4, 2013
2,867
Cost efficient is relative to the person, not the device.