By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

Balacing a locomotive power unit

How is it done in practice?

All Topics | Latest Posts

Search for:  in Thread Title in  
Tim Stevens15/01/2018 16:16:14
avatar
1618 forum posts

A question following the recent article on making loco wheels - how are locomotives balanced?

I know the simple answer is that bob weights are built into the driving wheels. but ...

On each side of the engine, there is a need to balance the out-of-centre rotating mass of the wheel connecting rods, and the reciprocating masses of the piston, the valve mechanism, and various links and twiddly bits. If the wheels and their links are in perfect balance, there is nothing to reduce the fore and aft forces from the piston assembly, in time with the crank pins, or the valve gear, at some other angle depending on the design. On the other side of the loco, the same values of fore and aft forces remain, but 90 degrees out of phase and well out of line with the other side.

If nothing is done about this, there will be a double fore and aft pull on the drawbar, and the passenger's heads will all nod in unison, in time with the driving wheels. If too much is done about it, at some (high) critical speed, the wheels are going to leave the track each revolution, and at different times each side. Either way, the loco will rock too and fro, shaking the fireman's tea from his enamel mug.

Neither is a good idea, so in the real world (and in the model world) what is the formula, please?

Regards, Tim

duncan webster15/01/2018 16:52:38
4100 forum posts
66 photos

I've sent the acting editor of ME an article on exactly this topic. Hopefully he will publish it.

Tim Stevens15/01/2018 18:07:06
avatar
1618 forum posts

Thanks, Duncan

I hope the Acting Ed does better than 30 x 106 when what was intended was 30 x 10 to the power of 6. As any schoolboy will tell you, 106 does not a million make. [ME 4578, p156, top of column 4]

cheers, Tim

Roger B15/01/2018 19:38:35
avatar
192 forum posts
82 photos

This was one of the major problems with conventional steam locomotives. The various out of balance forces used to cause significant damage to the permanent way. The introduction of diesel and electric locomotives greatly reduced the damage and allowed greater axle weights and power outputs.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Support Our Partners
Eccentric Engineering
cowells
Rapid RC
Dreweatts
Eccentric July 5 2018
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate