Author Topic: 1/3 Scale Austin Seven  (Read 8044 times)

Offline Mike R

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Re: 1/3 Scale Austin Seven
« Reply #30 on: October 09, 2023, 04:17:54 PM »
Also, what is the coating or treatment done on the rods?  It looks great (as does the rest of the engine)!

Offline nj111

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Re: 1/3 Scale Austin Seven
« Reply #31 on: October 10, 2023, 09:01:36 AM »
Wow, this is truly exceptional!  Would love to see more detail of how you went about machining various items. Well done !
Nick

Offline Austin Seven

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Re: 1/3 Scale Austin Seven
« Reply #32 on: October 10, 2023, 06:02:34 PM »
Thanks all.
The crankshaft is machined from 50mm EN16 round bar. I sliced the sides off to create a flat plate, then machined most of it in the milling machine. I have tried to machine cranks before only in the lathe and have spent many an hour digging the bent crank out of the ceiling after it left the lathe in a hurry.
The finish on both rods and crank is from shot blasting.
If it looks good leave it, if it doesn't paint it or better still shot blast it.

The first picture is the crank being machined, the second is the distributor to get a sense of the scale.

Offline Roger B

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Re: 1/3 Scale Austin Seven
« Reply #33 on: October 10, 2023, 06:13:38 PM »
Excellent  :praise2: 
Best regards

Roger

Offline John Roberts

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Re: 1/3 Scale Austin Seven
« Reply #34 on: October 10, 2023, 07:10:06 PM »
Incredible machining. How did you make the crankcases? They look like really good castings. Lost wax?
  I have a friend who has had Austin 7's for over 50 years. I can't wait to show him your photos. Please carry on showing us more pictures!!!

Offline Admiral_dk

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Re: 1/3 Scale Austin Seven
« Reply #35 on: October 10, 2023, 09:19:36 PM »
Quote
If it looks good leave it, if it doesn't paint it or better still shot blast it.

 :lolb:   :lolb:

But I do agree that it looks really good after you have 'Blasted it'  :praise2:

Oh - what kind off shot blast material, Gun and preasure ?

Per           :cheers:

Offline Austin Seven

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Re: 1/3 Scale Austin Seven
« Reply #36 on: October 14, 2023, 09:50:39 PM »
The shotblast is small like an air brush using aluminium oxide.
Here are a some more pictures.

Offline Austin Seven

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Re: 1/3 Scale Austin Seven
« Reply #37 on: October 17, 2023, 07:07:15 PM »
Hi All.
Has anyone had experience of very small, high torque electric motors that can be used as a starter motor?
I have very little package space. 22mm diameter x 40mm long. I've tried quite a few, but all have gone up in smoke.

Offline Admiral_dk

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Re: 1/3 Scale Austin Seven
« Reply #38 on: October 17, 2023, 08:21:26 PM »
I would expect that you need at least one, if not two, more gear stages to reduce the RPM's and increase the Torque enough ....  :old:

How that is going to fit into the space available to look right - is a bit unknown ....
This kind of brings us to - that not all parts scale equally well  :(

Best wishes

Per      :cheers:

Offline uuu

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Re: 1/3 Scale Austin Seven
« Reply #39 on: October 17, 2023, 09:02:55 PM »
Tiny geared motors do seem to exist: https://www.ebay.co.uk/itm/GA16-050-DC-12V-33-340RPM-Gear-Box-Micro-DC-Geared-Motor-DIY-Car-Robot-/225658570241

Not that I have any experience here - just sniffing around the problem.

Wilf

Online crueby

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Re: 1/3 Scale Austin Seven
« Reply #40 on: October 17, 2023, 09:41:58 PM »
What speed does the output shaft of the motor have to go? And do you  have an idea of the torque needed? I've  done lots of looking around at gearmotors for models, those numbers plus the sizes you gave would help a lot in narrowing it down.


Chris

Offline Admiral_dk

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Re: 1/3 Scale Austin Seven
« Reply #41 on: October 18, 2023, 09:20:00 AM »
Interesting suggestions Wilf  :ThumbsUp:
.... and I see that there is a World of different ones too  :o

My best guess is that the Crankshaft should be turned somewhere between 120 to 240 RPM - and I do not know what the Final Gearing to the Clutch-Basket is - but I'm sure that 'Austin Seven' can help us with that info  ;)

Per         :cheers:

Offline Vixen

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Re: 1/3 Scale Austin Seven
« Reply #42 on: October 18, 2023, 12:02:32 PM »
Hello A7

Most small i/c engines have a very fast tick-over (2000 to 3000 RPM ish)  compared to their full size counterparts. I have always found a small engine will start better when using a cordless drill in the high speed range rather than the higher torque, low speed range. For your Austin Seven, I would aim for a crank shaft speed of at least 300 to 400 RPM, perhaps higher. You will definitely need a one-way clutch to disengage the starter motor after the engine fires.

Mike   :thinking:
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline ddmckee54

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Re: 1/3 Scale Austin Seven
« Reply #43 on: October 18, 2023, 03:36:21 PM »
You'll find lots of gearmotors, but your space limitations are a real killer.  You can get small-ish planetary gearmotors that will give you around a 300 rpm output, that would probably have the torque needed to turn over your engine, but those guys are typically 25mm in diameter and I think the length is 60-75mm?

The only gearmotors that I can think of that will fit in you available space are the little N20 gearmotors.  They are tiny, only about 10-12mm thick, 15-20mm wide, and maybe 30mm long.  (They are definitely NOT round, and in no way resemble a starter motor.)  Those are available in a variety of output rpm's, and motor voltages, but I doubt that they've got the oomph to turn your motor over.  They've only got a stall current of about 0.6A.  If you were making a non-working engine with no compression, they'd work fine.

Don

Offline Austin Seven

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Re: 1/3 Scale Austin Seven
« Reply #44 on: October 18, 2023, 04:15:47 PM »
Many thanks to all for the replies.
I start the engine at the moment with an electric drill set to fast as per Mike's comment. That's about 1600rpm (no load). The flywheel has 87 teeth, the starter gear has 14. That would require a starter speed of about 10000 rpm.
By the time I've finished with this, I think the starter motor may end up bigger than the engine!

I've attached a picture of the dynamo (3 phase alternator with three phase bridge rectifier). That took a long time to design as I wanted a 6v system with about 0.5 - 1 amp.

Rob

 

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