Motor Advance

[Ian]

With 20+ years experience in the hobby, I'm embarassed to ask this but..........

Does it matter which way a motor is advanced, and if so which is the correct direction?

Thanks

Ian

[Dave Treacy]

er, yes!

If you are holding the can with the endbell up, then the endbell moves anticlockwise to advance timing. :D

[James_Stewart]

With the endbell facing you, rotating it anti-clockwise advances the timing, and clockwise retards the timing. Don't retard the timing below 0 degrees though....



Pah, beaten to it!

[Joost van Leeuwen]

Nitpickmode -> No since you can only advance it in one direction ;)

You need to turn the endbell the opposite direction the armature is running.
Armature is running CW so the endbell needs to move CCW. (Looking at the endbell, not the bottom of the motor)

[mark Fuller]

i know how to advance mod motors but i was just woundering what does it do

iv heard differnt things

[mark Fuller]

IN TURMS OF MOTOR SPEED

[Dave Treacy]

Mark, simplisticly put, the higher the revs (the more advanced the timing) the lower the torque.

Although current stock motors run 24 degrees of advance timing, it would be unwise to set a mod to this, generally 8-12 degrees is most economincal on the comm.

[MattW]

Mark, My own interpretation/thoughts would be that more timing extends the power band of the motor. i.e more RPM. Ther is of course a downside, in that it usually takes longer to get to it' smax RPM, and often generally takes longer to accelerate.

For 12 turn touring car racing, we ofter wind it nearly as far as it will go, i have run 24 deg of timing many times. Generally at the moment i haven't been going as high as that, usually sticking around 18 for a 12 turn.

[PDW]

Ian, it is important to give the motor some advance. Although designs are improving every year, the same basic tenet holds true.

Under load, the motor retards itself. You should always run some advance so that (as Pete Stevens used to say) "it knows which way to turn!" In the days before motor limits, we used to run motors at about 5 to 8 degrees advance. If you wanted more power, you simply changed to a 'hotter' motor!

Today, the same situation applies in 1/12th scale - 7-turn anyone??!!

[Snails_Pace]

In my experience advancing the timming increases torque accross the rev range as well as increasing the R.P.M. The disadvantages being reduced motor life, increase in running temperature (could account for drivers experiencing reduction in power) and an increase in current draw.

I agree with the comments above for ideal setting being 8-12° and for 12th use a lower wind rather than increase the timming.

In my experience with running the timming the wrong way it generate a lot of heat, draws alot of current and delivers very dissapointing performance.

[MikeS]

Under load, the motor retards itself.

Interesting comment Pete, care to expand on that thought........

[PDW]

Mike,

I only wish I could, but my science is not good enough!! It was one outcome of a long conversation, many years ago, with Mike Reedy. I was trying to research an article that would explain (simply) how different winds of motor can be assessed for on-track perfromance.

The theory is that a single wind of X turns should have the same electromagnetic performance as a double wind of Y turns when assessing wire cross-sectional area. However, whatever the calculations say, this just doesn't work out in practice.

Mike said that the interaction of the fixed and reversible magnetic fields, as the load increased, caused the motor to retard (it's timing). However, as the motor load decreases (motor speed increases) the timing 'comes back'. And that is as far as I can go!!

However, this does correspond with the effects we see on the track - an advanced motor does come out of corners better and gives more top speed. (MattW's interpretation in reverse - I don't agree with his observation) This same effect was also seen on the John Reid motor dynos that the Schumacher Team used in the early '90s. This correlation leads me to believe that Mike's statement is broadly on the mark.

[MikeS]

Hi Pete, I wasn't disagreeing, it was just the way it was put, it was more a case of...wow that goes back a ways......both showing our ages I think ;)

If you want a more comprehensive explanation, read on and I will try to explain it more fully.

Firstly, it was the phrase it "retards" itself that caught my eye. Since, physically, nothing actually changes. To understand the actual principle you need to understand exactly how the motor works with regard to the magnetic fields. Everyone does (or should) be clear on the physical commutation/switching process and how that works, and that there are magnetic fields involved, but the motor only works and delivers the power it does simply due to the WAY these magnetic fields grow, interact and then collapse, repeatedly and in boring succession.

The magnets in the can, produce a permanent field, in such that it is always there (permanently). The coils, on the other hand, produce a varying switched field, varying since it takes time for the electrical current to develop the coil energy which saturates the stack plates and creates the eventual armature magnetic field pole. It is switched, since as the comm rotates, and the polarity of the coil windings are reversed - switched!

The motor works on 2 levels, it uses both the attraction and the repel interactions of magnets, at the same time, and the comm is the switch that controls when, and which polarity each wind will have. In our current (ages old) design and construction of 3PW/2M motors (3 pole electromagnetic wind armatures - 2 pole permanent magnets), when one pole is moving into an attraction phase, there is always another pole moving into a repel phase, while the third pole with be either fully attracting, or fully repelling, depending on exactly where in the cycle you are. So in reality the moving states cancel each other out - how well they do is one part of the motors efficiency ability.

Once a pole stack is fully saturated, pushing more energy into the coil will not produce any more power, all it will do is cause a heating up of the windings and hence the motor - the problem also is that to ensure full saturation you actually have to go past the full point, if you see what I mean!
The most efficient motor is one that stops pushing anymore electrical energy into the coil once the stack is fully saturated, but since this is all mechanical, with no feedback sensing, it cannot be designed and timed to do this at all rotating speeds - saturation time is a constant, the rotating of the motor rotor is not. To produce a motor with the highest efficiency, all we have to do is to ensure that the power is terminated as soon as the stack pole is fully saturated, easy to say, but not so easy to do since our motors all have a fixed timing and comm-segment/brush width. Obviously I am ignoring the potential to incorporate something of this ability in a good ESC, but that is another discussion.

So, to get back on track........

The so called "retarding", is more a reference to the interaction that takes place during the attraction pole phase only, where the two magnetic fields are pulling towards each other hence the rotor will move towards the opposite attracting magnetic pole, but, there is also a distortion that takes place as the two magnetic fields begin to interact, on the advancing side this will result in the permanent magnetic field distorting towards the advancing rotor field - which could be described as having caused a temporary distortion to the permanent magnetic field such that the effective timing of that pole of the permanent magnet was retarded (pulled backward). The exact opposite is happening on the opposite repelling pole phase, so in reality this is cancelled out for the most part (hence my interest in your original comment).

The other problem with this is that while it was something that could happen with the relatively low powered (field strength) magnets that we had some 20 or so years ago, this does not generally happen in the motors we use today - unless of course your can magnets are weak! In the old days, the coils were more than capable of overpowering the magnets, i.e. they could quite easily produce a far higher field strength than the permanent magnets. But during the development of the of the motors that we use today, the magnets have improved at a huge rate compared to the field strengths, in fact I would argue that the main (only!) increase in the coil field strengths we get today are almost completely down to the increase in supplied voltage that the winding are now getting with the modern highly efficient motor controller and of course the much higher and more sustained cell voltages we see, even under load.

So, I hope that was easy enough to digest and made sense. In our motors, "magnetic retardation" was something that happened yonks ago.......but not in anyway to the same degree with todays motors... :D

[Ian]

Right - silly question time again I'm afraid.

Why when I retard the timing does the RPM increase?

[MikeS]

And I am afraid an equally silly response - it depends on from where to where?

[Ian]

Retard in relation to the centre point - I've noticed that if I retard the motor timing (i.e. turn the end bell in the wrong direction) then the maximum RPM is significantly higher when compared to the highest RPM achievable when the motor is advanced.

[MikeS]

That will normally be true since the motor is not under any load, and so it will also spool up faster. However, this really is no indication of how well it will run under load. Of course it also assumes that segments are correctly lined up with the stack arms on the armature!

If you read my lengthy post, you should have realised that there is actually NO correct timing, only an optimum one that works for the speed (shaft rpm) band that the motor spends most of its time. Its all a huge compromise, what is best for punching out of corners is less timing, where as what is best for sustained high rpm is higher timing. Don't forget that the brush contact patch width also has an effect!

I had one mod motor (no names) that I could not figure out at first, that ran best at approx 3deg retarded - as in 3deg behind the Zero datum, on closer inspection it turned out to be the comm segment moulding was not correctly aligned, by a considerable amount - it can happen!

[PDW]

Mike,

Many thanks for the detailed explanation, it is appreciated. If I had known that then .......!! :D

Ian - this is the point I was trying to make to MattW. Advancing the motor narrows the power band. Providing you get that band correctly related to the road speed, the (advanced) motor comes off the corners better and has higher top speed. However, if the road speed drops, then you fall off the (narrower) power band and the motor won't spool up.

I think Mike's points explain the phenomena you are seeing. Also, everyone should learn that there is no correct advance for a motor with adjustable timing - only the amount that suits the track and your driving style. Stick to 1/12th guys - if you want more power you simply bolt it in!! ;D

[johnbull]

Pete. Mike. Greetings from Malta.

WOW. What a very interesting one. Thank you both for the free lessons.

This is what's so great about our hobby. It's a constant learning curve. I am sure I am considerably older than both you young gentlemen, yet here I am still learning more about motors and how they tick.

Thank you both.

Actually we are now down to running 8 x 1s. And boy do these cars fly.

Thanks again and regards

Joe from sunny Malta.

[MattW]

Pw, yeah i see what you're saying. I didn't say what i was meaning properly the first time ;D and still not sure i could now, so i'll give up!!!!!

[PDW]

Joe - I see it is b****y sunny in b****y Malta again!! ;D ;D LOL! It's a few degrees above zero here and damp - ugh!

You guys have an advantage in this area by not sticking to the 12-turn limit. I hope that the novices don't think that they need 8-turns just to keep up! This limit has a lot of support amongst the majority of club racers here.

MattW - never give up!! I hope that Mike's excellent explanation assists your understanding. If it is any help, even winds (doubles, quads) give generally more torque across the range, and so are better if you let corner speeds drop. Odd winds (singles, triples, quins) tend towards a narrower power band and do better on longer tracks. Knowing this, and the explanations above, might help you get more feedback from your timing adjustments.

Or, you can do what I do - enough timing to show it which way to go, gear up a bit and go easier on the throttle out of turns. I find this simpler and workable. :)

[Dave Treacy]

Pete, let me see if I've understood you correctly. The scenario is that with "good" cells in a 12T, you are starting to dump at the end of the race. Rather than chage the gearing, try reducing the advance timig for extra duration?

Dave

[MattW]

Dave, I think (generally speaking) less timing should have lower current draw and hence may well be an option if you are struggling.

PDW, Must admit is nice not to race with motor limits, i used an 8x2 at Mold :o

[johnbull]

Hi Pete. Greetings from Malta.

Firstly the weather. Sorry to upset you but yes it has been glorious the last couple of days. It poured all day Saturday. Was dry and Sunny Sunday when we had a championship meeting, and it poured again Monday. You could say we were lucky!

It's great now. in fact a couple of us took the afternoon off yesterday and went down to the track to lap it up.

Re motor limits. This is how we work it so beginners don't get daft. We have 3 classes - all 1/10th touring cars. Class 1 is for raw beginners - 1st year racing. This class uses a Corally 21 turn single sealed control motor. Corally actuallymark the motors for me and no unmarked or tampered motors may be used. We limit this class to 3000 cells and races are 8 minutes. This keeps them reasonably slow.

In year 2 drivers move up a class to Super Stock. Same 21 turn motor but 5 minute racing with 3300 cells - much quicker. There is a grading system here. The top 3 at the end of the championship have to move up to mod.

Finally the modified class. mod motors with no limit. 3300 cells.

It works well and those control motors are dirt cheap. I sell them for GBP 17.00.

We have run this system for some years now.

Regards

Joe from sunny Malta.

[Snails_Pace]

OK Chaps the picture below shows the power curves on the same motor with same power supply (6V 4AH gel cell battery) altering only the timming. The max power output can be read out from the onscreen text as well as the colour coding for each trace.
Click for Power graph (http://www.hwmsc.co.uk/Timming Analysis.jpg)
You can clearly see that power across the whole rev range is increased for timming up to 24° and that at 36° the power is less but the revs climb like mad.

This must the advantage of having dyno, you don't have to think too hard about where your load is and how its affecting the magnets etc. you whack the motor on and display the readout!!! Try a few different settings and hey presto you find the ideal setup for your motor.
(Graph produced the MVRC Racing Power Meter)

[mark barord]

A question for Snails-pace. Is that graph displaying rpm and time on the x axis as I would have expected the motor to produce it's max power at different revs for each differing amount of advance.
In my experience inceasing the timing moves the peak power point up the rev range. It also increases the peak revs of the motor so increasing the area under the graph, which my A level physics tells me equals the power of the motor.
It would be interesting to see the same experiment conducted on a graph that shows torque and efficency on the same graph. This realy lets you see the sweet spot of the motor.
Note to PDW; John Reid's dyno was realy good for the mid eighties wasn't it?

[MattW]

Mark has just said what i was trying to say ;D cheers MB

must admit i agree that the dyno graph looks a little odd to me, not sure i't actually telling you anything as there is no mention of time and peak power should be at a different point with diferent timing.

[DA_cookie_monstA]

Graph looks ok to me, as all it is depicting is the power produces at certain parts of the rev range for different timing vairables.

The only way you get to alter the way the motor performs, characteristics wise is with rewinding the motor, different brushes or different magnets.

It would be interesting to see a table of power, torque, RPM and efficiency though.

[PDW]

Dave - yes, that is what works. However, don't forget to look to your ratio too. Most importantly, try driving with less throttle on the existing setting first.

Joe - I like your class system, especially the 8 minutes for beginners as it gives them more driving time just when they need it.

Mark - ahhh! those were the days. Motors whizzing on the dyno, and that ace F3 racing game on the BBC that John wired up to a transmitter!!

Oh Snails Pace, where do I start!! First off, Mark is right - your graph is about as useful to a racer as a chocolate teapot!! :) It looks to me as though there is no significant load on the motor during the run-up phase (I can't see a time line on the X Axis). Secondly, if there were a significant load and a time line, the dyno could calculate the torque and current draw against time - vital to my third point. Efficiency. It doesn't tell me what efficiency the motor is running at to achieve these 'staggering' figures.

What John Reid's machine proved all those years ago was that the efficiency tails off as the timing increases. Today, no one bothers with that since 3300 cells will deliver bucket loads of energy, so we 'can't' really go flat. Like all racing engines, efficiency is sacrificed for power by simply screwing up the timing - but some racers still need efficiency. Nice try, won't wash with me! ( ;D LOL)

[Snails_Pace]

The dyno works by spinning up a flywheel and by timming each revoloution of the motor under the load of the flywheel a caculation for torque is possible. The flywheel has been calibrated, the timming on the dyno is very accurately measered ±1 microsecond (1 millionth) and calculations made by people with countless maths and physics degrees so what you see is what you get out of the motor at the various rev ranges.

The traces shown on the graph are power on the vertical axis and R.P.M. on the horizontal just the like power output graphs for car engines. There is no need to take time into account on a power/rpm graph as this has already been factered in to calculate power at the varous revs. Power in has not been taken into account as basically there is only really need to show power output for ascertaining a motors on track performance (unless you are dumping).

Once you have run few motors on the dyno and then run the motors in racing situations you soon learn how to relate graphs to actual track performance. In my experience of racing 12th circuit cars and relating the data to cars performance it is true reflection how the motors perform. Its a fantastic tool for predicting a cars performance in a race as well tunning the motor (via brushes and springs) for optimum performance.

One of the features of the software you get with the dyno is that it simulates a drag race with readings taken (albeit with no ineficeincy taken into account). This does show that when you select the optimum gearing for any length of drag strip a better time is possible with the motor advanced to 36°.

There is no need to show torque on the graph as power=speed x torque and so for any given R.P.M. if the power output is higher, the torque will also higher.

Lastly these graphs are for a specific motor (orion chrome touring which has been uniquely abused by myself), different motors exhibit different characteristics as has already been pointed out so it is more than likely that on a different motor the power band and max RPM will change in different manner to the test motor in this example.

[marcoski]

I personally see no problem with the graph, it shows power output for various timing angles just like Brian said. What does however surprise me is that despite changing the timing, max power occures at the same RPM! With most motors I have played with on the dyno, changing the timing moves the RPM at which max power is developed. The only motor I have found to be relatively unresponsive to timing change, apart from the the current skyrocketing, is the reedy TI. This just seemed to like 12 degrees! It just goes to show all motors are different, and your ability to interpret the results from the dyno and apply them to the car on the track is far more important than the raw results themselves.

[PDW]

Marcus - I think you have answered your own question! There is something wrong with the graph since it does not show what is expected; what has been shown on (other) motor dynos for years, and what is predicted by the Laws of Physics!!

Snails Pace - you can't convince me. There are a whole heap of gaps in your statements. One example - what weight is the flywheel, and do you have a range of weights that reflect the car's weight factored by the mechanical advantage of the gear ratio used? When using a flywheel this is necessary. When using a mechanical brake (as in a real dynomometer) the process is quite different.

I am not getting at you, but a whole army of people with degrees in computing, physics, maths, neuroscience, etc., etc. write software - for Microsoft. Nuff said, eh?!! ;D

[Snails_Pace]

I'm not trying convince anyone of anything all I have done is show the results of a simple test on accurately calibrated equipment. If you wish to perform the a similar test on equipment you have had calibrated and document your result then fair play, if you have no other information on the subject I recommend you just leave it alone and accept that my motor performs in the documented manner.

To be honest I have tested other motors which perform on the test in exact accordance with current expectations discussed on the thread. It was my intention to prove that the peak power was reached at a higher R.P.M. with less torque at lower revs. But hey I performed a test and it came out different to general expectation yet in keeping with how it 'feels' on the track. I like a punchy motor and guess what? with that particular motor, just out of pure tunning on the track I ended up running it just below 24°. I did not choose this motor on purpose, it was on my work bench at the time and I decided to run it up.

I think this goes to prove the idea that there is no overall best position for the timming on a modified motor.

If anyone wishes to test the motor in question simply bring your test rig down the High Wycombe MiniStox Club, let me know that you will be there, I will bring the motor along and you can test it for yourselves. On the previso that you book in and race the meeting.

Look forward to seeing you.

[MattW]

Torque can be very important, as it can play a very important part in gearing. Just because "power" increases does not mean that torque has increased. I believe that it is quite possible for torque to drop, but RPM increase by a greater amount, and hence power would be increased.

I don't doubt that a dyno is a good tool. Although i don't own one i have used one on many ocasions. If you know what you are looking at/for then they can be very useful.

Personally i am not convinced that by looking at power alone you are getting it's maximum potential.

Having said all that it's a while since i played with a dyno, hence i could be talking out of my..... ::)

[Mark Stiles]

Power = Speed (RPM) x Torque

Advancing the timing increases torque across the rev range (as I understand it). Thus, advancing the timing gives more power at the same RPM. Both the graph, and the equation above prove this (i.e. if torque increases, so will power with RPM remaining constant).
   However, there must be a point at which the motor’s timing has been advanced too much (in this case 36 degrees), thus reducing torque and subsequently power at the same RPM.
   The optimum rpm for max power doesn’t change because the motor advance creates more torque. So if we are increasing power AND torque, we can rearrange the equation as follows;

Speed (RPM) = Power
Torque

Therefore, if both values are increased in proportion with each other, then RPM will remain the same.

So the graph is useful in that it tells us that 24 degrees is the optimum advancement setting for maximum power to be achieved. Now the motor must be geared so that the peak of the graph is reached when the car is at the end of the straight (i.e. the maximum RPM of the motor in the race should be approximately 13 500 RPM). Trouble is, the required gearing (especially if it’s a track with a long straight), coupled with the timing advance may mean that you dump (even though you’re getting max power out of your motor!). Also, running that much timing will significantly increase brush and comm wear!

So Marcus, am I right? (thought I’d ask you as you seem to have the most knowledge of electronics here, and I’ve only studied it to GCSE level!).

[marcoski]

In theory, you are right, in practice, there are other factors that affect where the torque is at a maximum and where power is at a maximum, and they do not usually occure together! Mikes long post goes some way into explaining some of these effects, but there are others. Rotating machine theory can fill quite a large book if all factors are taken into account.

As has been stated in Mikes post, and others, there is no ideal timing position for a motor, rather a sweet spot has to be found that allows the motor to perform optimally given your gearing, surface and driving style. This can only really be found by experimantation on the track, having found the sweet spot, returning the motor to the dyno may well show that what is good on the track is poor on the dyno compared to your best dyno result. Also, flywheel dynos present a fixed load to the motor, generating optimal timing results for that fixed load. Your car, on the otherhand, presents a widely dynamic load on the motor, based on gearing, track and driver input. It is hardly a surprise that what is best on a dyno is not usually best on a track - I remember Matt White once saying "My dyno ,ie my left thumb, tells me that xxxx is better than yyyy", despite a couple of pages of debate clearly showing that yyyy should be better. How the car feels to the left thumb is by far and away the best indicator of how the motor is performing in real life.

[Mark Stiles]

I've always had my suspicions about dynos. Why pay as much as £200 for something that isn't necessarily useful?

Even if they were proven to be pieces of kit, I would much rather have my left thumb intead of a dyno, as it means I get to drive/race more!

[DA_cookie_monstA]

Dyno's ARE an important tool, but for those who can interperet the results properly, set the motor up, and be a good judge of the gearing it will need.

If you can't do that, best leave it as stock from the supplier, or pay someone to do it for you.

[PDW]

DCM - dynos are an important tool, but the things that are used for measurement these days (and that produced the graphs I 'dissed' earlier) are NOT dynomometers - they are merely static tests.

For all the reasons Marcus, Mike, Mark B and I have given, please accept that you are not testing the motor dynamically - on a dynomometer. What you are in effect doing is driving a car from 0-60, graphing the engine, and then saying that it will be great from 50 to 90!! As anyone who has driven a BMW 330d will tell you, it is slower to 60 than a 330i, but from 40 to 140 it leaves the petrol version for dead!! Go figure their torque and power curves!!

Mark S - I, like you, am going to save my money!!