Gearboxes that will drive back

[goodmayes]

Bemf controllers are effectively analog servo control systems. They continually sample the motor speed, compare it with the setting value, and if there is an error, apply a different voltage (or pulse width if a DCC chip) to the motor until the correct speed is resumed. The extra or less voltage is usually in some proportion the the size of the error, so that it will rapidly and nearly completely correct almost any amount of error. And all that happens at electronic speed.

 

Usually, in the case of model bemf controllers, if the model motor is going too fast, dropping the applied voltage significantly will allow the inherent motor load and friction to slow the motor sufficiently and almost instantly. So it's unlikely that even a worst-case all spur gear system going downhill will stay noticeably in over-speed.

 

But there is nothing to prevent good bemf controllers being able to apply a correction that includes up to a full reverse (braking) voltage to the motor at the higher end of the error range. And such a controller will be able to hold any loco at the set speed on the most severe downhill grade, at least until the angle at which the wheels will slip.

 

Ted

[artisan100]

"But can we please get back to the O/P is there a gearbox that will drive back in 4mm available? "

 

There is now.

 

See www.cometmodels.co.uk

 

Geoff

Comet Models

[DLT]

And to take things full circle, Slaters recently announced this:  https://slatersplastikard.com/linePage.php?code=SG4&directory=/others/gearboxes

A "direct replacement for the Portescap RG4" attached to a Mashima motor.

It doesnt state that it will "drive back", but describes an "all metal combination of crossed helical and spur gears".

Hope this is of interest!

Cheers, Dave.

[Miss Prism]

Driveback or no driveback, it would be nice to have some bearings in a box costing £100.

[artisan100]

"it would be nice to have some bearings in a box costing £100."

 

I agree, but the width of the gears precludes anything other than plain top hat bearings in 00, and the price is not just the box, but the Maxon motor as well. The trials have included a loco weighted up to over 500g and with a train consisting of 10 Comet metal coaches doing laps of an oval that is 35' long and includes a 1 in 100 gradient on a curve for over 15' of that run and there has been no discernible wear.  

 

This is not intended to be, and never will never be, a mainstream product, but is simply made available for those people who have a desire to use coreless motors and crossed helical gears. It's another option.

 

Geoff 

Comet Models

[artisan100]

It would be easy to provide alternative fold up etches, but whether it would be cost effective, given the expected sales, is a different matter.

 

Geoff

 

Comet Models

[flubrush]

This is not intended to be, and never will never be, a mainstream product, but is simply made available for those people who have a desire to use coreless motors and crossed helical gears. It's another option.

 

Geoff,

 

I'll pop a mention in the up-coming August edition of the S Scale Gazette.  The RG4 used to be a popular motor/gearbox combination for S scale modellers in the UK and there might be interest in your product.

 

Jim.

[artisan100]

Thanks, Jim.  I sent details to the mags and EMGS and Scalefour Soc, but forgot S Gauge Soc.  Sorry. 

[Horsetan]

I do hope more people will take this up. It's momentum and mass we should be replicating.