Belt drives - any clues?

[chris251]

I've recently bought a set of pulley and drive belts to fit into a 009 model engine I've been building.

Because of space constraints, the motor (8mm x 16mm 5 pole coreless) has to drive a layshaft, which then drives another layshaft with a worm gear, which drives a coupled axle.  The belt drive is located between the 2 layshafts, and I also have a pair of gears which can fit in the same space as an alternative to the belt drive.

For some reason, the belt drive causes about twice as much friction as the alternative gears, is this normal for a belt drive? - lots of people seem to fit belt drives directly off these motors without trouble, but this seems to be causing far too much friction.

The belt is 6.7mm internal diameter x 0.7mm round cross section, the pulley root diameters are 1.75mm and 5.2mm, and the spacing is 6.0mm, calculating this gives an 11.1% stretch to the belt.

 

Does anyone have any advice on how to reduce the friction caused by a belt drive or am I best to just use the alternative gears?

Edited February 26, 2021 by chris251
corrected belt stretch

[Miss Prism]

There is a horrible tradeoff between belts gripping their pulleys sufficiently not to slip, and thereby causing excessive friction in the pulley bearings, and belts not gripping their pulleys enough but allowing the pulleys to run reasonably freely in their bearings.

 

[DCB]

The  belt drive has the advantage of being quiet and of slipping if the motor is overloaded, which is really useful if you have a powerful motor and fragile final drive, But round or square belts sap power and when you have a gutless Coreless motor that leads to overheating and failure. I would use spur gears myself, or a flat belt.   I have used traction tyres as belts in the past on Jouef locos.   (Swiftly flogged on on eBay)

[chris251]

Thanks for the quick replies, I was thinking if I should use the spur gears instead.

 

1 hour ago, DavidCBroad said:

But round or square belts sap power and when you have a gutless Coreless motor that leads to overheating and failure.

by round and square belts, am I right in assuming you mean when located on 'V' profile pulleys?

The pulleys I'm trying here are 'V' profile and round profile belts.

 

[Izzy]

I’ve used Nigel Lawton’s drive belt system - square belts into V pulleys - and found it works quite okay with the right tension, which is key. It also uses a 8x16 coreless and only the loco weight limits the haulage capacity. The main advantage is it’s quieter than fast running spur gearing, and larger gearing reductions are possible than with gears using the same shafting distance. But spur gears can cope better with load transmission when variable friction through the total drive train is an issue.

[decauville1126]

I've never been a fan of belt drives - early experiences with Lone Star diesels - but have ended up with several these days on the "Nigel Lawton" principle of square belts and V-pulleys, the belts canting into vees and pulling into the pulleys. I think the same system is used on cd players and other electrical stuff.

 

What I have found is that after standing unused for some time, in my case years, the belts take on a set and slip. But I tried a touch of TackyWax from Deluxe Scenics and it seems to help, so much so that I can now live with the system.

 

O-rings have very little stretch and so will sap power. Square belts becoming V's in use will pull into the V-pulley and may also have an element of throwout in the event of transmission braking. Quietness is also a benefit.

[chris251]

I've just bought some of Nigel Lawton's square belts, and run a simple test with the same mechanism just swapping the belt, and measuring the electrical current going into the motor at various voltages:

 

with the o-ring (6.7mm diameter by 0.7mm cross section), the motor runs at 30mA, (at 6V)

wheras the square belt (6.5mm diameter by 0.6mm cross section) runs at 20mA, (also at 6V)

and from the pitch of the sound of the motor, it also runs faster and more freely with the square belt fitted.

Result - Nigel Lawton's square belts seem to perform better than o-ring belts.

[Izzy]

59 minutes ago, chris251 said:
Result - Nigel Lawton's square belts seem to perform better than o-ring belts.

Yes, in theory square belts in a V pulley should have greater surface area grip than O’s, which seem to have been born out by your real life test comparison. Thanks for the info.