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Old Sep 07, 2014, 06:04 PM
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How to measure a brushed motor

As new in the RC World I try to do things easy and economic. Many "rc toyboats" have quite a nice hull and runs nicely in the water. To start with my son a good and educational way we have had a nice summer with rc toyboats. Now we will go further without spending a ot of Money on completely new boats and rc-equioment. Our idea is to use the hulls (boats) and the brushed motors BUT buy a good transmitter with reciever (we have already done), install an ESC (BEC) and servo. I have understood, which is obvious for me, that it is not good to install a to small ESC.
Our questions are theese:
1. How to measure a brushed motor without having it to run in water? Is there in the market a brushed motor checker that can be used?
2. Why is it not good to have an ESC that can take a lot higher Amp than needed? I have read this somewhere.
I would very much appreciate to get some information and advices.
Björn
Sweden
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Old Sep 08, 2014, 02:51 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Björn,

I gather you're refering to the ampdraw of the motor, not it's size?

When you can provide some pictures and measurements of the boat & motor & prop used, we can make an educated guess which ESC to get.

1) Only if you have the motorsize and the code of the manufacturer stamped on the motor, you may be able to trace that back to the specs.

Otherwise it's rule of thumb for the ESC:
10-20A for a small scale model
20-40A for a small speedboat (watercooled if required)
40-60A for a larg(ish) scale model
60-100+A for a large speedboat, watercooled.

2) That's nonsense.
An ESC too small for the motor may shut down thermally, or burn out, too large is only an issue if the ESC is too heavy for the model to carry.

Regards, Jan.
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Old Sep 08, 2014, 03:26 AM
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For item 2, in pre electronic control days, a controller consisted of a heavy duty resistance. This had to be perfectly matched to the motor as too high a resistance caused nothing to happen until full throttle, then it all happened. Too low a resistance ( = higher current rating ), as soon as it moved off normal, the motor would go full speed, again, with no real control.
With electronic controls, what will handle a large motor will equally well handle a small one, provided that the motor can handle the voltage supplied. The constraints are size (will it fit?)and weight (will the boat carry it?). And cost.
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Old Sep 08, 2014, 09:52 AM
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To evaluate a brushed dc motor you need to measure speed (rpm) and amp draw. Both of these can be done in various ways and don't have to cost lots of money.
One consideration to buying an ESC closer to what your project needs is cost. More amps, more cost.

Dave
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Old Sep 08, 2014, 04:39 PM
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hanks for answers. I ean Ampdraw. I will measure the Engines ad so on and come back.
Björn
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Old Sep 09, 2014, 05:54 PM
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To make myself more clear my wish is to create some simple boats to go with 2,4GHz rc-system as well as with low costs give my son and myself some boats to "play with" and att the same time learn about the rc hobby. That´s why we wish to "rebuild" the rc-system in boats we already have from to simple 27 and 40MHz systems to something better. I also have my task in our village to try to get young people interested in other things than computers, facebook a.s.o..
We want all boats to go both forward and backwards. We need to invest in recievers, ESC (BEC) and the right servo in each boat.
We will use FlySky FS-TH9X upgraded 9chanels as we do not like the stearingwheeltype. We hope they come from Banggood soon as they where sent 5 weeks ago!!
I describe our different boats as below: (European MM translated to inch by deviding with 2,54)(Lw=Length waterline)
1. A small racingboat L: 20", Lw: 15", W: 6". Plastic hull. 2-blade prop 1,26". Motor Brushed L: 1,18", W:0,95", Shaft: 0,08", Geared down to about 2:1. Probably more than 10 years old found att a second hand.
2. Modern racer 1:16, produced 05/2014 by Newqida, China, nr.757T-6031A.
L: 31,9", Lw: 21,6", W:10,2". Plastic hull. 2-blade prop 1,54". Racing-rudder.
Motor Brushed Watercooled L: 1,97", W:1,42". Gear closed and not able to study. Shaft 0,157 (4mm).
These are the two first. As I do not know how long message I can write I will descibe the other three in next message.
//Björn
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Old Sep 09, 2014, 06:30 PM
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Here are the other:
3. Wooden modelboat from 1954 built from a kit "Komet" by my grandfather a rather good modellbuilder at that time. It was meant for petrolengine but for me as 8 year old it was delivered with a smal electric motor without radiocontrol. A new electric motor were mounted ablout 1979 Mabuschi RS-54 (3 polar). I am willing to swap the motor in this boat as well.
L: 23,6", Lw: 22", W: 7,68". Shaft prop 0,15" (4mm). Prop rather big, maybe needed to change.
4. Fireboat 757T-4022A, scale about 1:32. Now with two smal motors mounted under the boat. I will cahnge to a one-prop constuction with normal rudder. I hope to be able to use one of my old Mabuschi-motors from the 70ths. My son will use it together with me when I use my Robbe Feuerlöschboot (Robbe 1195).
L: 15,4", Lw: 13,6", W 145.
5. Graupner Rivera RTR (new)(art.no.2111RTR), my doughters boat. 2,4GHz.
Unfortunately no information about the motor. No gear. The boat is equipted with a combined receiver and ESC without a bindingknob which I mean is a necesety to be able to rebind a reciever a) for our transmitter and 2) when a receiver loses its memory. That´s, losing memory, is a problem I have had with my Monster Truck from HPI Maverick with bruschless motor. I have written to Graupner that I do not think this combined receiver/ESC without binding.knob is the standard Grupner is known for. The answer was not an expected one.
To this boat I will put in a new receiver and a new ESC. Otherwise it works ok.
- We also have a harbortug 23" that we will take a bit later. A nice boat from China that we will repaint and train my son in electronics etc..
- With this information I would very much appreciate to get advises what to buy - first sizes and than suggestions to suppliers. Buying from US is ok but I have to put on a 35% for customs.
Thank you all very much in advance.
Kind regards
Björn
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Old Sep 09, 2014, 07:28 PM
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I am not overly familiar with all the boats listed but I do know the workboat from china, I have one. Great little boat actually and the motor is a good motor out of the box, the rest of the gear has to go. There is a position in the back for the rudder servo to go, just remove the "bang bang" servo the factory used, I used an inexpensive waterproof ESC and a 2.4ghz radio for it. I also removed the "water ballast" system and I use a 6v 4.5ah SLA battery for power and ballast. You have to seal the holes in the bottom of the hull and if you cut open the ballast tank it makes for a perfect battery tray. The last thing I did was removed the mast and tower. This is a pretty heavy structure for the top of a small boat and caused a lot of instability. As soon as it was removed the boat handled better.

If you don't want to buy parts from the US I honestly don't blame you. I found a hobby store in England that has great customer service and fast shipping even over the pond. Try looking at Westbourne models. Best place I found for anything boating.

Massey
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Last edited by Massey; Sep 09, 2014 at 07:29 PM. Reason: Darn'd auto correct
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Old Sep 10, 2014, 05:28 AM
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Sneek, Netherlands.
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Hi Björn,

Could you provide some pictures of each boat, external view and some of the innards.
We like pictures, it also gives us an idea of what you're working with.

Regards, Jan.
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Old Today, 05:44 AM
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Thank you for your answer. Now we have pictures and I have had help from my lovely doughter to incluse the pictures. I hope it will work. I send the pictures in the same order as the discriptions above. I waite with big interest for you suggestions for our boats.
Thanks in advance
Björn
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