Author Topic: Doddys HaupWerkstatte - My build thread  (Read 2752 times)

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Offline John Candy

Re: Doddys HaupWerkstatte - My build thread
« Reply #30 on: Apr 19 2019 09:32 »
I have (after a year or so of frustrating R&D), got the doors to work on my G class (later Q23) District line motor car.

Well done.....this I must see!

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline Doddy

For no other reason than . .
« Reply #31 on: May 17 2019 15:12 »
to see if I can.

After a pleasent weekend photographing ex-LT1938 tube stock on the I-O-W. I decided to see how to drive the 2'  7" wheels from an ex-DVD motor.

First the new Griffon Hovercraft

And delapidated tube stock at St Johns Depot

And a bite to eat at the Ryde Pier cafe - well in order! Service was excellent and freshly cooked food - delicious!

After establishing that the wheels axle needs to turn at 500rpm to achieve a prototypical 45 mph, the DVD motor is rated at 6500 rpm. Calculating a double reduction gearbox using this website proved useful.

Prior to that Ineeded to understand the relationship between an Axles rotational  speed and Miles Per Hour. So back to the PC and a short blast on an Excel spreadsheet.

Using the SMEX calculator I derived a 13:1 double reduction gearbox configuration.

I don't intend building a tube train, but found the process helpful to get my mind around gearbox design. I trust others will find the information useful to them.

"You don't know what you don't know"

Offline Peaky 556

Re: Doddys HaupWerkstatte - My build thread
« Reply #32 on: May 17 2019 21:34 »
“...the DVD motor is rated at 6500 rpm.”

Just capturing a line from Doddy’s workings, as a general comment to anybody thinking of designing or choosing their own gearbox or ratio, it is not appropriate to use the free running speed of the motor.   Not that I’m assuming the 6500 rpm is the free running speed in Doddy’s case, but the reality is that maximum power is achieved at about 50% of free running speed. 

Consequently if we hope to work a small power unit hard to get the top speed we want, it’s probably wise to gear the motor for 50% revs at the speed we want.  Then if power is a bit marginal, it’s more likely to run as we want, and if it’s overpowered, it’s just a matter of treading gently on the ‘go’ pedal.

Generally these thoughts are a bit academic though, as most suppliers of motor-gearbox units wouldn’t tell you the speeds or ratios anyway!


Offline Doddy

Re: Doddys HaupWerkstatte - My build thread
« Reply #33 on: May 17 2019 23:38 »
My thoughts exactly Tim, many thanks for drawing them out.

Your assumption of my using a maximum speed at 6500rpm is therefore correct.

In the case of any potential 1938 'Tube' car, I envisaged that I would not want it operating much (if at all) above a scale 35mph, so the 50% powerloss would have been almost irrelevant in my particular case.

As for monitoring the motor speed, I just treated myself to one of those hand held laser gadgets you use yourself to count the rpm on spindles - cost £8.72 inc p+p comes complete from Guangdong with a Chinese 'dump Trump' cap and flag.

"You don't know what you don't know"