What replacement for brushed

[Stephen Belshaw]

I have been persevering with a marriage of old and new tech, namely a brushed "Graupner Speed" motor with a twenty year old "Jeti JES350 ECO" and new LiPo batteries. These were powering a Graupner Match airframe, twenty years old but newly built and with a AUW of a tad under 900 grammes (compared to the original design weight of 1.25Kg).

It does run and flies very well (fast) but is obviously overpowered as twice it has snapped a prop in flight with fairly hairy consequences, although the airframe has survived! I'll have to throw the towel in with the old school stuff and, if possible, convert to brushless. So I'll need a direct replacement for the Speed 500 which will have the same dimensions (presumably an in-runner) and a suitable ESC if my Jeti cannot work with the new motor.

This is the current motor/ESC combo:

 

And this is the battery:

 

Is a suitable motor available that will slot in to the airframe/existing mounting holes?

Edited By Stephen Belshaw on 12/09/2019 15:58:27

[Simon Chaddock]

First I would have to say that a prop breaking twice in flight suggests something is seriously wrong with your motor prop combination. It really should never happen.

The Graupner Speed 500 BB is rated at 17 amps continuous. If you are within its specification then on a 2s (8.4 V) LiPo the motor is using about 150W.. It is hard to imagine a prop braking at this power level so your prop may be significantly over loading the motor. You will need a Watt meter to measure the amps actually being used.

A brushless motor requires a matching brushless ESC.

This leads to the next problem. A 150W brushless motor is tiny, both in size and weight, compared to the Speed 500 so it is likely the plane is likely will have to be re-balanced (battery moved forward?) to maintain the correct centre of gravity.

The chances of a direct bolt hole replacement are very slim.

I am not sure what a 'Graupner Match' actually looks like but it appears the conversion is going to take a bit of work to achieve but the end product will be lighter and have a longer power on duration as a result.

[Stephen Belshaw]

Simon, thank you for your comments. Having already significantly reduced the weight of the model with the use of a LiPo and re-positioning the battery accordingly I doubt I have any adjustment left in that department so would have to make the difference up with lead. Not a problem as I am already well under the design weight.

Running a 8" x 4.5" folding prop my watt meter gave a max reading of 250W, I queried the use of the Jeti ESC with the UK distributor and received this reply " the JES 350 Eco was designed to work with 6 to12 Ni-XX which is 7.2 to 14.4 volts so should be fine on a 2 or 3 cell Lipo".

This is the airframe:

[Keith Berriman]

Could I suggest a call to George at 4 max the maybe able to suggest something

[Simon Chaddock]

Stephen

Its not the voltage that is the issue but the amps. If you are drawing 250 W from a 2s LiPo then that's 33 A which is pretty close to the Jeti's limit of 35.

As you suggest an in runner will likely be easier to fit as they use nose mounted bolts like the brushed motor but I suspect you will have to go to a 4s LiPo to get the Watts.

This in runner from Hobbyking should fit in the space and on a 4s is adequately powerful at 300 W with a 7x4.

The range of out runners is much larger (and are usually cheaper) so one could be found that would match the power of the 500 brushed motor on your existing 2s but as they are usually rear mounted are more difficult to fit in an existing fuselage.

[Stephen Belshaw]

Thanks again Simon, I wonder though if I need 300W - flying it with 250W seemed plenty fast enough and is giving me around 130 watts per pound so does that leave the door open for retaining the 2S set-up??

RC Plane Flyer, thank you for that suggestion I'll have a look at 4 Max and perhaps give George a call.

[PatMc]

I don't think that there are many inrunners of the correct dia that would be a straight drop in fit to replace the 500 brushed motor. However there are some "outrunners in a can" that meet the criteria, MVVS make some apparently very good quality but also very expensive.
OTOH Hobbyking Gliderdrive motors are similar in layout, more reasonably priced & have a good reputation.
This one is 1400 KV & should be good on 2s with something like a 10" or 11" prop, unfortunately it's not currently in stock.
My personal choice for the model would be this 960 KV version of the same motor which would be best on 3s with a 10" or 11" prop and it's in stock at the UK warehouse.
The power requirement can of course be regulated by choice of prop.

IIRC the first version Graupner Match that you have has a plastic (Plura?) fuselage. I've been able to upgrade a couple of same era Protech plastic fuselages from brushed 550/600 can motors to outrunners without too much difficulty.

This is a re-furbed Protech Unlimited, at 63" span it's a bit smaller than the Match & I normally fly it like a powered slope soarer - 10 - 15 secs of WOT then aeros on the glide repeating the cycle from a fast pass at head height until the battery's low.
A model the size of the Match is more versatile, I'd use it for mixed aeros & thermal hunting depending on the potential lift conditions & my mood but I always only use full power for a fast, up to 30 secs, climb with any of my gliders followed by aeros or thermal hunting.

BTW I notice that HK's warehouse stock seems to be very low (I've been looking for motors & batteries), I presume it's a result of the civil unrest in the area.

 

 

Edited By PatMc on 12/09/2019 23:54:16

[Geoff S]

I have a Gliderdrive motor in my Phoenix 2K. I think it's the 960kv version. It's very convenient and neat with the connections at the back removing the need to be careful how you run the wires to avoid the spinning case (which in these motors is contained in an outer shell anyway).

As Pat says, you can set the power output to whatever you need simply be choosing an appropriate prop. I think I've under-propped mine because I didn't need the extra power.

Geoff

[Erfolg]

Patmac

I am really pleased that you have drawn our attention to these motors, although I now mostly fly sport and scale, I can see these motors being really useful in a model I will be assembling with a radial cowl. Previously I have used the Turnigy high torque inrunners, as these no longer seem to be stocked, it is a potentially excellent solution.

As for breaking props on a few hundred watts, I have only manged that when using Chinese folding blades. For folders it is Aeronaut or Graupner. 200 watts is nowt, as we say up here in the North. Start talking Kilowatts then some will start waking up.

[Stephen Belshaw]

Thanks for all the help and advice chaps, I asked George at 4-Max and he recommended this motor along with a 9 x 5 prop.

These are now inbound, along with a few other bits, so I should have the "Match" up and flying again shortly.