Motors ...for beginners - please keep it simple

[Dusty]

Cant beat a "Watts up"  meter  to know whats really going on

[Tim Mackey]

I'm with Dusty here - I ALWAYS suggest using one rather than relying on these calculators,which in my experience are often way off reality.

Which actual motor and prop and battery are you using Trevor?

[trevor grace]

Hi Tim

Im going to try the Dualsky  260W  870Kv  (XM2834CA-10) with a 1800mAh 20C 3S and

 an 11x5.5

Trevor

[Tim Mackey]

That should be fine, and you could likely increase the prop a tad more too.

We are drifting off topic slightly here- this section is for  really simple questions and answers - please feel free to post on another thread as we get more into results etc.

[Shane Sunday]

Hey Tim. Quick question for ya. Does the motor voltage rating mean the amount it can handle? I have two 3s 2300 11.1 lipos that I want to run in series. This would make them into one 6s 2300 22.2v battery. Will this push 22.2 volts through my motor and kill it? These threads a a god send by the way. Thanks Shane

[Tim Mackey]

That depends on the motor Shane. Sure applying 22V to a motor ( or to anything if it comes to that ) will bee seen as 22V, but Its generally current that kills 'em rather than just voltage. However,  if everything else stays the same ( prop and motor ) doubling the volts will double the current too, and likely let out the magic smoke.

Excessive voltage may also cause another problem...that of excessive RPM, which can overstress bearings and magnet fixings etc.

[Ed Anderson]

Posted by Shane Sunday on 19/10/2010 00:23:07:
Hey Tim. Quick question for ya. Does the motor voltage rating mean the amount it can handle? I have two 3s 2300 11.1 lipos that I want to run in series. This would make them into one 6s 2300 22.2v battery. Will this push 22.2 volts through my motor and kill it? These threads a a god send by the way. Thanks Shane

 

 

 

 The first question I always ask is, why do you want to do this?.

 

If you double the voltage your motor will try to run at double the RPMs.  In order to turn the same prop at twice the RPMs will draw a LOT more amperage. 

 

Ignoring the specs on the motor for a moment, this might overdraw the batteries.  If your motor is drawing 30 amps on a 3S 2300 20C pack, it is doing fine.  If you run two of them in series your amp draw might hit 50 or 60 amps, which will likely destroy the lipo packs.

 

Will your ESC handle this kind of current or voltage?

 

So, I ask again, why do you want to do this?  What do you hope to accomplish?

 

More speed? 

 

Longer duration?

 

Heavier plane?

 

What is the goal?

Edited By Ed Anderson on 19/10/2010 13:24:17

[Shane Sunday]

I had been searching the web looking to get a longer life out of the batteries when I came across running them in series. ( sorry guys trying to keep on topic here) I found out that parallel will give me a longer flight time but I was curious about the power/speed increase to the motor when run in series and didn't want to sink more money into more lipo's and also didn't want to fry my motor.

 

The voltage rating on my motor is 7.4- 15v but I was unsure if that meant that that was the least or most they could take. there were many things I've learned from reading these forums but the min/ max volts was something I was unsure of.

 

Thanks for the help.

[Ed Anderson]

Just as you said, that is min and max.  Should be clear now.

 

Running your lipos in parallel will give you longer flight time with no adverse impact on the motor or electronics.  You might see a small increase in speed/power as you will get less voltage drop so prop speed may be a little higher for more of the flight, but well within specs, I am sure.

 

Typically running in series will shorten your flight time as it will increase amp rate.

Edited By Ed Anderson on 19/10/2010 16:16:19

[Biggles' Elder Brother - Moderator]

Two quick simple (I hope) questions for you Timbo.

 

I'm putting an electric powered model together as a simple winter hack and as you know electric is not my thing! So I need a bit of advice. The motor in question is supplied by JP and is an EnERG C35-20 1100kV with a 5mm shaft.

 

1. The model comes with one of those electric motor mounts in the form of a plywood box. My motor has a "cross" form mounting plate which screws (via four inner holes) to four holes in the stationary part of the motor casing. My problem is that the spacing of the outer mounting holes in the cross mounting are not suitable for the plywood mount - they are either too close to the edge or clash with the edge joint.

 

The pitch of the cross mount fixing holes in th motor could fit the plywood mount. So the question is...could I fit some 3M studing into he holes on the motor, fix that with a lock nut, then fix the studing directly to the plywood mount. Effectively doing away with the "cross mount" piece?

 

2. If I do this the motor shaft will face the wrong way - I assume if I loosen the various grub screws this will go through to stick out the other end? I ask because I had a go and it didn't budge - even after a hefty "tap" with a hide mallet! At that point  chickened out!

 

BEB

[Tim Mackey]

Should be OK I guess - alternatively, could you either drill new holes with less spacing into the spider mount...or perhaps fit a larger front firewall to the ply mount ?

Is there any way you fit the motor from "behind" the firewall, using the front mounting screw holes in the motor end plate, with the rotating can behind the firewall IYSWIM

 

The shaft may also have a recessed circlip on one end, so after checking everything is removed setscews etc....a good blow with a decent plastic faced mallet or similar should free it off.

[Biggles' Elder Brother - Moderator]

Thanks Tim.

 

I can't place the can behind the firewall as the shaft wont reach to the cowl exit point then. I did think of making a "false front" as it were to mount of the ply mount - but was trying to avoid that if poss. The new holes in the cross mount is a good idea - I'll take a look at that. Failing that I'll go to plan A.

 

BEB

 

PS Just thought of something. Putting the can behind the firewall might work if I put some spacers behind the plywood box - Mmmm, I'll think about that to. Thanks again.

[Erfolg]

Biggles

 

A simple dodge would be to mount the standard aluminium mount onto a piece of suitable ply (adapter plate), sized to accept the mount and be capable of fitting onto the firewall. Any nuts and screw threads being recessed in either the ply plate or the existing "fire wall".

 

The ply plate is then  fastened to the existing fire wall. The weight increase would be manageable/acceptable, compared to other methods.

 

I am far from convinced with regard to the aluminium frames commercially available. Easy to install they may be, yet I suspect not as strong, for the same weight thin ply box.

[Biggles' Elder Brother - Moderator]

Thanks for the advice Erflog. These electric jobbies are slightly foreign territory to me. I'm puzzled as to why even very expensive, top end, electric motors come with no instruction manual or information what-so-ever - most importantly a dimensioned drawing giving the thread sizes and hole spacings. You have to measure everything!

 

BEB

[Erfolg]

Biggles

 

I suspect you have more experience than I have.

 

What experience I have, is quite narrow, certainly in respect to electrics.

 

With regard to mounting details. Most of the motors I have purchased, particularly from GC and HK, have come with a simple single sheaf paper with mounting details.

 

With respect to motor performance, this is generally sparse. CG does have links in some cases to Dr Kiwi who has tested some motors.

 

Using the data in the description of GC, BRC  and HK is a useful starting point, in conjunction with comments by modellers.

 

None the less I have experienced some difficulties. I recently purchased an inrunner to replace an existing failed unit. The starting point, which indicated an output circa 150w, resulted in circa 110w. The deliberation was, should I reduce or increase the prop dia. Working on the notion of Power = 2piNT, it was a case of higher revs and lower torque, against lower revs and higher torque. The problem was I had no curves for torque etc. I tried a smaller propeller, as I had one. I was surprised that the watts went down. I bought a larger set of blades and still have not got to where I want to be. In this instance, I know which way I need to go.

 

Nearly every set up to date, has required some experiment. I have considered a test stand, such as Timbo/Dr Kiwi examples. To get max benefit i still need a tacho, although knowing the thrust would be a step in the right direction  

[Chris Bott]

BEB can you do away with the ply box?

 

I always try to and then make up a mount out of a ply disk, some allthread and the ally cross.

 

Screw the ply disk to the firewall and all remains adjustable.

It becomes very rigid when all is tightened up. 

 

 

[Biggles' Elder Brother - Moderator]

Hi Chris,

 

yeap that's the conclusion I was coming to. Its simple and I like simple! I was just a little worried it would not be stiff enough, but you have reassured me on that.

 

I might do it in two stages. There are 4 holes, with captive 3M nuts fitted, in the firewall and the existing ply box screws to them. I'll remove the box and make a new ply plate held by four short lengths of stud fixed into those holes. Then I'll drill this plate to match the spacing on the spider and use another four studs to connect that. Alternatively I'll just put 4 new holes in the original firewall and run one lot of longer studs if the spacing on the firewall is suitable.

 

Pass the 3M studing!

 

BEB

 

 

[Steve Hargreaves - Moderator]

BEB if its only 3mm studding I would watch the length you use. If its too long then it will probably flex or whip....remember that electic motors supply max torque at zero revs & can kick pretty hard when they start off. An option might be placing a 3mm id thick walled tube over the studding to make it more rigid....

 

You probably already know this!!!!!!

[Chris Bott]

The 4 studs really do go very stiff once everything is tight.

 

Obviously different sizes need to be used for different sized motors, but I've been pleasantly surprised just how small you can go. 

 

In one set up the studding acted as a crumple zone and almost certainly saved the motor from damage. You don't need to know the circumstances but we have all been there... 

[Biggles' Elder Brother - Moderator]

Job done!

 

Sorry about the out of focus piccy - one day I'll figure out how to use a "automatic" camera. You're right Chris the 3mm studing does form a remarkably stiff structure. When I first put the studs into the captive nuts in the firewall and tightened them up with a washer, nut and lock nut I wasn't too convinced. But on adding the ply plate and the spider then tightening everything up nice and snug I was very pleasantly surprised.

 

A further benefit - I've just fitted the cowl and of course the studding makes it really easy to "fettle" the spinner/cowl gap! Not only that but I'll be able to adjust the down and right thrust really easily.

 

I could get use to this electric lark!....well maybe...

 

Anyway - thanks to everyone for their advice chaps - another triumph for the forum!

 

BEB

[Chris Bott]

Hi B.E.B

 Glad your'e happy. 

 

There's one difference with yours that has the potential to cause a problem. But you should be OK.

 

I put the ply plate at the firewall end of the studs, and the front of the studs pass through the ally cross. This way there is plenty of "gap" for cooling air to pass out of the motor.

The way you have it, the cooling air can get out but then hits the ply immediately. 

 

I have had one motor overheat badly with the ally cross bolted to a bulhead, it was cured using the rearranged mount. 

 

Here's a pic I happen to have of Danny's Wot4 that may show it better.

 

Edited By Chris Bott on 22/10/2010 23:25:07

[Biggles' Elder Brother - Moderator]

Good thought - easy enough to change! Just swap the studs over between the hole sets!

 

Or drill a hole in the centre of the ply plate!

 

Thanks Chris.

 

BEB

Edited By Biggles' Elder Brother on 22/10/2010 23:33:20

[Danny Fenton]

Thats a very stretched piccy of my poor old wotty,

 

Still going strong I hasten to add on the same pack of A123's and that mount hasn't budged

 

Cheers

Danny

[Chris Bott]

It's this silly forum  It's a portrait photo and they always get squashed. Click on it and it looks fine...

[Malcolm Fisher]

Just acquired my first brushless outrunner. As someone said earlier there are no instructions...

It seems that it's possible to mount the prop on either end as there is some sort of adaptor to fit the shaft and one to fit the other end of the motor.

Is there any advantage in either case?

To me it looks easier to mount the prop on the end of the motor case rather than on the small diameter shaft sticking out at the other end especially in terms of keeping the wires out of harm's way, The exposed motor casing could also benefit from being out in the airstream to aid cooling.

Am I totally up the creek?

Malcolm