speed 400 x 3!

[Den Moran]

Hi, everybody!

I recently bought a rare Graupner Ju 52 kit, complete with the three speed 400's in the box. I understand that it only needs one speed controller, as the motors are connected in parallel to one (I think!) battery.

Does anybody have any experience/suggestions/wiring diagrams with the circuit I would need to set up, please. I have no experience with brushed motors at all.

I hope to start the build in January (after a nearly completed Tony Nijhuis Hurri, a nearly completed HK catalina, and a Flite Test Seaduck! ). Also, I would like to use corrugated covering, but it may take too long!

Thanks, everyone,

Den,Swansea.

[Alan Gorham_]

Den you have already explained how the motors are wired in your post!

All in parallel to the ESC, then to the battery. Very simple and less wiring than brushless motors.

[Romeo Whisky]

You probably know this, but don't forget you'll need an ESC designed for brushed motors.

A brushless ESC won't work.

[Den Moran]

Thanks, both!

So I just need to work out what size/capacity brusehed ESC I will need. Any ideas on how to work that out, for three motors, please?

Thanks again, Den.

[Shaun Walsh]

According to the plan it uses a Graupner Pico-Mos 33 brushed speed controller and a 6 or 7 cell Nicad battery so you could probably use a 3S Lipo but not sure how easy it is to get a brushed speed controller that big. Someone is selling a Pico-mos on ebay though.

**LINK**

 

Edited By Shaun Walsh on 29/10/2019 07:30:36

[Trevor]

There's a review of this on my website:

Junkers 52 Review

I'm happy to try to answer any other questions but it was 24 years ago and my memory isn't what it was!

Trevor

[Trevor]

P.S. Having just re-read that old article - make sure you read it all the way down to the P.S.!

Good luck with the project.

[Alan Gorham_]

ESC sizing....

I wouldn't guess, I would fit a motor with the prop I intended to use and connect it via a Wattmeter to the battery I intended to use, measure the current draw and multiply by 3 to give the current draw for all 3 motors.

Choose an ESC with a current rating about 20% higher than the current draw for all 3 motors as headroom.

Your biggest problem might be finding an new brushed ESC. You may have to look for a used one.

PS - I thought this kit came with a dedicated power set (motors, props, ESC). Even if your kit doesn't have this set, does it not have some documentation on the plan or in the instructions?

 

Edited By Alan Gorham_ on 29/10/2019 09:54:53

[Den Moran]

That's great,boys, thanks. I have not checked the kit since it arrived, but will get on it later. I'm sure you have given me all the info I need, Cheers, Den

P.S.

Re: the robbing gov of indeterminate parentage's efforts to sting us for £ 9, all our members are flatly refusing to pay it!

[Den Moran]

The kit didn't have one, so I ordered it from ebay, Shaun - nice one! That's it, folks, I'm good to go, keep you posted. Still tempted to try the corrugation, but I'll read Trevor's review first. Den

[Shaun Walsh]

Looking at the spec for the Graupner speed 400 motor

**LINK**

It seems that you may be limited to a 2S lipo because of the maximum voltage of the motor. Also the max current is 21 amps which in theory means you would need a brushed speed controller with a capacity exceeding 60Amps! I wonder if the reason that the plan shows a 33 amp speed controller is because the Nicad battery pack wasn't capable of providing much more current whereas a Lipo will. Suggest you attach an ammeter and run up a single motor and prop to check how many amps are drawn at WOT, if it's more than 10 Amps you may have a problem., even if it is less than 10 amps a nose over on take off will quickly fry the ESC unless you shut down the throttle immediately.

[Shaun Walsh]

How about three small brushless motors and three ESCs? Would probably be lighter and more powerful but not in the vintage spirit.

[Alan Gorham_]

Blocking current in the link you quoted is stall current Shaun. A Speed 400 cannot handle more than around 9A continuous before the brushgear gives in.

Therefore lets say you prop the motors for 8A each you can use a 30 or 35A ESC.

I did suggest the method of checking the current that you are advocating in my post of 0945 this morning....

[Shaun Walsh]

Posted by Alan Gorham_ on 29/10/2019 11:19:21:

Blocking current in the link you quoted is stall current Shaun. A Speed 400 cannot handle more than around 9A continuous before the brushgear gives in.

Therefore lets say you prop the motors for 8A each you can use a 30 or 35A ESC.

I did suggest the method of checking the current that you are advocating in my post of 0945 this morning....

Thanks Alan, never used brushed motors so my knowledge is limited.

[Ben B]

I think in this day and age using nicads and brushed motors is the equivalent of hair shirts and self-flaggelation. It's possible but the question has to be why. When I returned to r/c about 15 years ago I had a flying wing with a speed 400 and for a while flew it on nicads (even then it was massively out of date technology). It was slow, flights were short and the motors burnt out there brushes and by all accounts it's best to "run them in" with no load in water (it all starts getting a bit painful).

I swapped to brushless inrunners and lipos after about 3 months and that sorted that out.

If a kit I was building came with inrunners, nicads, brushed ESC etc and I wanted to keep it completely stock I'd keep them but in a situation with no ESC (and ? no battery) I wouldn't even think going brushed. A 2000(ish) kV inrunner in a 28mm can will normally fit a speed400 installation without modification.

[Alan Gorham_]

Ben - it's a classic YMMV case I think. See below for some of my multi-motored scale models. All powered by brushed motors and in the case of the Lancaster still using NiMh cell packs.

On a multi installation you tend to be a lot kinder to your motors as there is less need to run each motor at full chat due to the efficiencies of having the propwash directly over the wings etc. Some of my models are very old now (between 15 and 20 years) and they have their original motors.

Don't discount the simplicity of using a single ESC and the easier and lighter wiring involved in a brushed installation.

[Keith Berriman]

Did I read somewhere that brushed motors and lipo batterys not that good 7.4 V 2 cell too low 11.9V 3 cell bit to much and brushgear wears out quickly ??

[Alan Gorham_]

There is some truth in that.

My Blenheim uses two Speed 600 7.2V motors on a single 2S 2200 Lipo so that is very kind to the motors.

My Halifax uses four 8.4V Speed 400 motors on 3S2P 2200 Lipo which is pushing the motors, but I have an excess of power and thus can fly at around half throttle which is kinder to the motors.

[Den Moran]

I don't think my nerves will hold after all the effort at building this formidable kit!

I'll probably go down the 3s - 2018mm - 2000kv route with a large ESC!

Thanks,again,everyone,

Den, Swansea

[Simon Chaddock]

Den

The voltage a brushed motor can handle very much depends on the amps flowing and the design and quality of its brushes. The voltage itself, within reason, is not a problem.

Just putting 11V on a motor than is already loaded so it is taking its full rated amps at 8.4V will nearly double the current so things will go wrong quickly.

However if the load is reduced (smaller or lower pitch prop) to keep the amps within the motor specification then apart from spinning faster no problem. In that respect really no different to a brushless set up.

The need for a Watt meter to measure what is actually happening is obvious.

[Piers Bowlan]

An interesting project Den, I hope you post some build photos when you get a chance. For those interested, I think this is the plan, here. If it were my project I doubt I would fit Speed 400 motors when cheap brushless motors would be so much lighter and more efficient. Each to their own however.