Brushless motor expertise required

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19 September 2013 at 16:21 #43858
Hans Kuhn
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@hanskuhn
Hi,

I'm researching whether to go brushless for my next boat, and I have a question for the experts.

I often see brushless motors described with a 'required' voltage, either with an absolute value, e.g.

http://hobbyking.com/hobbyking/store/__28765__hexTronik_DT900_Brushless_Outrunner_900kv.html

This is a 900kV motor with a 'required' voltage of 11.1V

Or e.g.

http://hobbyking.com/hobbyking/store/__18968__Turnigy_D2836_9_950KV_Brushless_Outrunner_Motor.html

This is 950kV motor with voltage range of 7.4-14.8V.

My question is, will these absolutely not work with a voltage lower than the specified range? If for example I wanted to run the first one on 7.2V NiMH?

I'm looking at lower kV motors for a tug, it would have to run a 40mm 3 blade prop without strain.

Thanks

Hans

Edited By Hans Kuhn on 19/09/2013 16:22:24
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19 September 2013 at 16:21 #5260
Hans Kuhn
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@hanskuhn
20 September 2013 at 20:21 #43879
ashley needham
Participant
@ashleyneedham69188
Hans. I would say that 7.2V would be fine. I am not sure why they specify the voltage ranges for instance 7.4-11.1 v…as opposed to "up to 11.1v" , All motors will run at lower voltages.

Do you have a reason for wanting to use a brushless motor?? I am afraid there will not be that much expertise on this site as to the use of brushless motors for tugs…

Ashley
23 September 2013 at 13:42 #43915
Hans Kuhn
Participant
@hanskuhn
Hi Ashley,

It's definitley not common to use brushless on tugs, but there's such a large range of brushless motors and speed controllers available that I thought there must be a suitable combination that could be used. The key thing seems to me to get a low KV motor to keep the revs down, and a good speed controller with reverse and maybe some other programmable features like start force adjustment.

I haven't made any decisions yet, so far I'm weighing up the options and costs and doing some research. I've only just started on the hull:

Maybe someone can comment on my options for brushed drive – would it better to go for MFA type geared motors, or something like Graupner Speed 500 E motors? I need to install 2 motors.

Thanks

Hans
23 September 2013 at 14:54 #43917
Dave Milbourn
Participant
@davemilbourn48782
Hans

As far as I understand it brushless speed controllers are not very capable of reversing, and brushless motors don't like running at the sort of low speeds you might want for manouvering a tug. I gather that some of the US-made ESCs are pretty good (e.g. Castle Creations) but they are hundreds of dollars apiece. Chinese ESCs are available at silly prices but their reliability and current-ratings are highly questionnable.
If this is a twin model then your choice of brushed motors would be either geared motors e.g. the MFA Torpedo 500, or high-torque low-speed straight-drive motors such as the Mabuchi 555 (either running on 12 volts).
The range of Speed motors – in a reduced form – is listed by the new Graupner/SJ company but quite what the availablility is just yet is uncertain. It's for sure, however, that neither the Speed 720 Torque nor Speed 900 are listed. Shame, as these were perfect motors for medium and large tugs. **LINK**
The Speed 500E would be far too fast for a tug without gearing down (about 3:1).

Dave M

Edited By Dave Milbourn on 23/09/2013 14:58:02
24 September 2013 at 13:48 #43927
Howard
Participant
@howard79726
Hans

Check out the Mega Mig 650 from Puffin Models (www.puffinmodels.com) which might suit your application. Pricey at £33.95 a hit, although they claim it won't need gearing. John Emms is very helpful if you give him a call there.

Howard
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