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Member postings for Bob Cotsford

Here is a list of all the postings Bob Cotsford has made in our forums. Click on a thread name to jump to the thread.

Thread: Chris Foss Xtra Wot
02/07/2020 11:34:30
Posted by Peter Jenkins on 02/07/2020 09:23:55:

Do you use the Max/Min function Bob? That needs a spare channel on the Rx though. You also get motor rpm if you connect to one of the 3 phase motor leads. If using a gearbox you can enter the gear ratio used to get prop rpm.

Connecting to FrSky I just use consumption, pack voltage and altitude. I had to go away and check the manual to remind myself what's available on the Unisens-E and what you meant by min-max! I have set up telemetry displays to show max power, max height on my transmitters but I tend to forget they're there most of the time. I generally browse the logfiles at home out of curiosity or if there was an issue but I'm not chasing every watt so I only tend to monitor lowest cell voltage for warnings of poorly cells. Any value that needs warnings (pack voltage, altitude) are set up as logical switches triggering special function 'play track' warnings, all within OpenTX.

I think it's the Bolero that I set up a motor lead for RPM but I found it a bit unreliable - sometimes it triggers, more often not.  TBH unlike with IC I don't worry about the RPM of an electric motor, after all I set it up with a known kv and known battery voltage so it's not going to vary that much.

Edited By Bob Cotsford on 02/07/2020 11:37:29

02/07/2020 09:11:46

The thing I like about the Unisens-E is that one unit can be swapped from model to model at the field. All you need is an SPort lead cable tied near your battery connectors. If you've got room for an extra 1 1/2" of connector they are a great upgrade.

Thread: OS 91 surpass disassembly
01/07/2020 16:44:44

The last cam bearing that I replaced I removed by filling it's bore with candle wax and tapping a close fitting pin punch into the wax, it came out without a fight.

Thread: Does anyone remember...
30/06/2020 23:29:45

I had a DC Merlin but I must have got a lucky one as I don't remember having problems starting it. I ran it in c/l models with an aircooled head and in an 18" Aerokits launch with a marine head screwed on. The one that beat me was the Frog 80.

30/06/2020 12:06:52

Nigel's Dad Eric was a keen flyer and we were in the same club (Lucas MFC) though I never saw Nigel with him or heard mention of Nigel flying anything.

Thread: Warbirds Replicas P51 Mustang
30/06/2020 11:28:46
Posted by Nigel Dell on 30/06/2020 09:51:32:

Was this known a two Cadillac of the Sky? 🙄😉

Would it have counted as a stretched limo?

Thread: Does anyone remember...
30/06/2020 11:24:51

Odd, I can remember my first RC model's name but not the name of the first girl I kissed down the side of Paul Dudley's parents house!

30/06/2020 11:22:41

Martin, a mate of my Dad's passed along one of those big ED sets with an APS Rhoma fitted with an ED Hunter 3.49. Never had much luck with that either. I did manage to fly the Rhoma into the school craft block one Saturday morning though! I too tried the published designs butmy first real success came with a commercial set in a big blue alloy case with a red button, REP, RCS? Locally made iirc.

I lost my first Mercury Matador in Sutton Park in the late 60's, the super-reg radio had worked ok in boats but the Matador drifted away downwind circling ever higher. Back to c/l for a while!

Thread: What glues do you use?
30/06/2020 10:28:41

A quick update on the canopy glue for pin hinges: I've attached the elevators and rudder to my Warbird Replicas La7 using 1/8" Robart pin hinges exactly as per the instructions, ie drill 5/64 or 2mm a shade deeper than the hinge will penetrate then relieve the entry for the knuckle joint. I counterbored with a 4mm drill to about 5mm. Paint the knuckle with petroleum jelly, smear the pin with glue to fill the bottom of the barb, then pump canopy glue into the bore ensuring the walls are covered. After a couple of minutes for the glue to soak in assemble the joint, I had barely any glue displaced outward so masking around the hinge was unnecessary and it seemed fairly solid after half an hour or so and I was pulling pretty hard. This morning I can't detect any movement pulling on the surfaces as hard as I dare and everything flops around far more freely than I've ever seen using epoxy!

canopy glue.jpg

Thread: Forum members' new models: Let's see them.
29/06/2020 10:39:08

What's that Barry, about 1500 dB worth? I see they all have exposed torque arms and pushrods, is there a reason they're not built into the fuselage? Is drag not an issue?

Thread: Ebay sellers...
29/06/2020 10:13:19

It's worth more because it's in original authentic condition, was built by an artisan and hasn't had amateur refurbishment, also it no doubt has good provenance. See, I watch Bargain Hunt!

Thread: What glues do you use?
29/06/2020 09:59:31

Mostly Evostick brand PVA, 30 min epoxy and various CAs for 'quick' jobs, local hardening, wicking in etc. For nose doublers it's solvent based contact adhesive.

Many years ago I built a Sukhoi aerobatic job from a pull out plan using CA for everything but the bearers, it was when superglue gels were appearing in model shops 'like balsa glue but better'. It built quick and light and when it hit the ground HARD it was the wood that failed - everywhere face 1. These days I limit my CA use due to the fumes.

I've just tried using canopy glue to fix Robart pin hinges into the tailplane and rudder on the basis it sticks like snot and is designed for plastic to wood joints. They certainly seem glued in tight and it's much less mess than epoxy which is what I've always used in the past. I'll see how well attaching the control surfaces goes later but I'm optimistic.

Edited By Bob Cotsford on 29/06/2020 10:01:05

Thread: Hanger Rash
28/06/2020 23:22:28
Posted by Tony H on 28/06/2020 11:55:51:

Humm, I waa hoping Solartex would be better, I heard old fashion Nylon and dope is the best for strength and staying tight.....

My 40 year old Veron Sopwith 1 1/2 Strutter is still covered in it's original doped nylon and is still as taught as ever, though it did need a coat of paint to cover the deteriorating Humbrol enamel paint job about 10 years ago.

Thread: Does anyone remember...
28/06/2020 23:13:52

While in and around Birmingham how have we missed Bob's Models, Jim Davis Models and my then local, Shirley Models run by Jim Knox(?) then later Mick Forbes. A later addition was Kings Heath Models in, you guessed it, Kings Heath and even later Birmingham Models in Acocks Green.

Thread: Motor Size
28/06/2020 11:41:42

Tosh, I've used these sizes on a number of .049 conversions, though personally I'd look for lower kv versions like the 1800kv ones I've got in order to use slightly larger props. I've just built a Blink delta using the 2212 1800kv on 3S, with a 6*4 iirc I'm pulling 180W, on a 2S battery it would be similar to a lower power 049, say a Cox QZ 049. 3S turning a 5*4 would be something like your TD049. Stick in a 20-30A ESC, 1000-1300 mAh cells and your in business.

To be honest, with these small setups you can pretty much use what's to hand/what will fit and play with prop size to get the performance you want. With my Little Bit that I first flew with a Cox Golden Bee I'd pop a 3 cell pack in for kicks or a 2 cell to potter about.

Remember, with electric you have a throttle and electric setups are much more flexible than a small glow motor.  You want less power?  Fit a smaller prop.  You don't have to run the power train at it's limits, in fact it's best to over spec everything a bit to give it an easier life.  It also means you can turn up the wick by simply upping prop size (within limits!)

Edited By Bob Cotsford on 28/06/2020 11:47:23

Thread: Does anyone remember...
28/06/2020 11:24:58

David - no, only home made rc from published circuits. Calling myself a TV engineer would have been polishing the Richard, I worked for a real rogue who rented TVs from a shop in Hall Green. Most of the faults back then were dry joints, the odd HT power transistor in Phillips or transformer in Fergussons, a power supply resistor in Deccas - all predictable stuff that needed little knowledge. Oh, and worn VHS heads of course where people used those god awful cleaning tapes. We had an account with RS iirc in Garrets Green. Horrible man to work for but lots of freedom once out on the road.

Thread: Repairing a 3D Angel "Jigsaw"
28/06/2020 11:11:14

I found canopy glue was the best thing for patching in new acetate/petg or whatever they're blown from. If you can find a similarly tinted pop bottle to cut a patch from the repair would fade into the background - if you're short-sighted and squint a bit cool!

My late friend Dave had a collection of Angel wings, all different colour schemes. I dread to think how many he got through over the years but if he ever damaged a wing he was pretty sure to have a suitable replacement under the benchangel

Thread: Saito 125A
28/06/2020 10:59:34
Posted by J D 8 on 28/06/2020 10:49:26:

OS looked to have dropped the idea from newer models.

I thought they'd gone over to using internal borings to provide a breather back into the inlet duct?

Thread: Does anyone remember...
28/06/2020 10:56:02

I have vague memories of a model shop over Tipton/Old Hill way, I remember one in Sparkbrook better from the 60s, Hancocks? Opposite side to the Vale-Onslow m/cycle showroom. Always had beautifully built KK Flying Scale rubber models hanging in the window. Then from the 70s there was Studley Models, in Studley of all places. Apple Models on the Hagley Rd near Quinton. I spent a number of years in the 70s driving around the Midlands doing NDT, then in the 80s doing TV repair work and could never resist stopping for a browse if I saw a model shop. I was the very definition of passing trade.

Thread: Hanger Rash
27/06/2020 22:48:47

I've just painted a rudder, ailerons and elevators, all covered from the same sheet of natural Solartex. The rudder was built up mainly open structure with sheet infill sections at the top and bottom, the elevators carved sheet and the ailerons veneered foam. The painting was done with rattle can acrylics in 30+ temperatures and everything left out in the shed to harden up overnight. Now the ailerons and elevators are covered in bubbles but the rudder is completely taught, both the open and the sheet sections. I'd completely forgotten just how bad 'tex can be depending on the structure. Now I think back I had similar happen on an all sheet Chippahawk decades ago, a lesson learned and forgotten!

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