R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 01-09-2002, 07:54 AM   #16
Tech Regular
 
Join Date: Aug 2001
Location: Finland
Posts: 250
Send a message via ICQ to JesseT
Default

Oh, another thing. I think the belt is tighter with the 20th pulley, just slightly. Still, talking with Teemu Leino, we agreed that the biggest difference comes from the changing of the motor position. Consider changing to the larger pulley: The layshaft comes backwards. Keeping the spur you need a smaller pinion and the motor comes backwards even more. This results both in a change of balance point and car's inertial axis. This difference you CAN feel although it might seem small.
JesseT is offline   Reply With Quote
Old 01-09-2002, 09:56 AM   #17
Tech Master
 
Join Date: Aug 2001
Location: England
Posts: 1,470
Send a message via ICQ to MattW
Default

sosidge, that only applies to people running the graphite pinions. I run fairly small spurs with what ever pullly (78/81) so i don't think i am going to get much smaller than that regardless.

Had i have thought about it i may well have been able to ask Cecil on Saturday.

I've got to be honest and stay that i'm still not convinced that there can be a difference either way. Although i am prepared to go with Jesse on the movement of weight.
MattW is offline   Reply With Quote
Old 01-09-2002, 04:48 PM   #18
Tech Champion
 
Kevin K's Avatar
 
Join Date: Aug 2001
Location: In a land of mini-mighty mental giants
Posts: 8,833
Trader Rating: 32 (100%+)
Send a message via AIM to Kevin K Send a message via Yahoo to Kevin K
Default

Boy Racer....I was not trying to make a point with you I was just saying what I noticed with the car. And I still dont see what you ment by what I said to Sosidge disproved anthing that I said. He said that they came up with the two pulleys because they dont have a large pinion spur choice and I was informing him that with the new car there is a greater choice in geraring then before.
__________________
2013 USVTA World Champion of the World
MOTIV RC presents the Midwest All-Star Carpet Series....15th year running 2017/18!!!
USVTA National Championship....check it out!!!
Im only responsible for what I say NOT what you understand.
Kevin K is offline   Reply With Quote
Old 01-09-2002, 08:40 PM   #19
Tech Addict
 
Mopar's Avatar
 
Join Date: Aug 2001
Location: Santee, Ca
Posts: 666
Default

boy666racer, I run stock class currently witha Tri P2k2 pro, and Sorex 36r tire with Hpi green inserts on Ofna split spoke rims.
__________________
Schumacher KF2se, Associated B5m CE (sold), Hot Bodies D413, Associated T5m, Axial Exo Terra, Schumacher Mi5, CRC 1/12, 3Racing FGX full suspension, Associated 18r
Mopar is offline   Reply With Quote
Old 01-10-2002, 02:40 AM   #20
Tech Elite
 
Cole Trickle's Avatar
 
Join Date: Sep 2001
Location: Denmark / Europe
Posts: 2,571
Default

Motor movement; I feel a pretty big handling difference, if I move my reciever (30 grams) 5 cm forward. The motor weight is approx. 150 grams, that is 5 times my reciever or about 10% of the weight of the hole car.
Cole Trickle is offline   Reply With Quote
Old 01-10-2002, 04:25 AM   #21
Tech Rookie
 
Join Date: Jan 2002
Posts: 9
Send a message via ICQ to Boy666racer Send a message via AIM to Boy666racer
Default

Mopar - your gearing seems a bit low! - Im not an expert on Stock Gearing though.

Matt, didnt u have a m8 who had some thing about this? - you said as Ashby that you would ask him! - did you ever remember?

Kevin K, I did not mean it as an insult, im sorry if you took it that way.
Boy666racer is offline   Reply With Quote
Old 01-10-2002, 11:30 AM   #22
Tech Master
 
Join Date: Aug 2001
Location: England
Posts: 1,470
Send a message via ICQ to MattW
Default

Chris, Funny you should say that as i asked him about it last night. He refuses to believe there would be any real difference.
MattW is offline   Reply With Quote
Old 01-10-2002, 12:01 PM   #23
Tech Champion
 
Kevin K's Avatar
 
Join Date: Aug 2001
Location: In a land of mini-mighty mental giants
Posts: 8,833
Trader Rating: 32 (100%+)
Send a message via AIM to Kevin K Send a message via Yahoo to Kevin K
Default

Boy racer.....I did not take it as an insult I just wanted to clear the air that I was not trying to make a point with you, I was just shooting out what I have noticed with the gearing thats all. No harm no foul.
__________________
2013 USVTA World Champion of the World
MOTIV RC presents the Midwest All-Star Carpet Series....15th year running 2017/18!!!
USVTA National Championship....check it out!!!
Im only responsible for what I say NOT what you understand.
Kevin K is offline   Reply With Quote
Old 01-10-2002, 11:12 PM   #24
Tech Addict
 
Mopar's Avatar
 
Join Date: Aug 2001
Location: Santee, Ca
Posts: 666
Default

boy666racer, have not actually run the 29/116 because of just changing to the 20t. This gearing is 1/2 tooth bigger than the the closest to the 34/116 with the 17t. Also do you mean low as in numerically? The motor runs very cool.
__________________
Schumacher KF2se, Associated B5m CE (sold), Hot Bodies D413, Associated T5m, Axial Exo Terra, Schumacher Mi5, CRC 1/12, 3Racing FGX full suspension, Associated 18r
Mopar is offline   Reply With Quote
Old 01-11-2002, 02:20 AM   #25
Tech Rookie
 
Join Date: Jan 2002
Posts: 9
Send a message via ICQ to Boy666racer Send a message via AIM to Boy666racer
Default

Mopar - Low as in mm per rev, you are only at about 27/28 mm/rev. The stock racers I know run as high as 39 or even 40 mm/rev!

Kevin - cool

MattW - well thats what i would have thought too!
Boy666racer is offline   Reply With Quote
Old 12-20-2002, 07:02 PM   #26
Tech Initiate
 
Join Date: Nov 2002
Location: SF Bay Area
Posts: 42
Default

This is an old post I'm dredging up, but have given some technical thought to it that seems to jive with experiences of Mission drivers.

I was looking at the issue from from the standpoint of kinetic energy stored in the layshaft assembly. After some digging in my old physics book, there are 2 main things to take into account:

1) The layshaft with a 20T pulley will have a larger Moment of Inertia (I) than with the 17T pulley. The physics behind this should be obvious, as a larger pulley has more mass and a larger radius, both contributing to increased inertia. The effect will be small, since most of the inertia of the layshaft assembly will probably be in the spur gear, even if it is lighter, it's radius is quite large, and that is where most of the inertia will come from.

2) The speed of the layshaft will be lower for the same ratio with the 20T pulley. We are moving in circles, so what is important is the angular speed (w). For example look at a final ratio of 7.2:1 with a motor spinning 20000 RPM, This means that with the 20T pulley, the pinion/spur ratio will be 4.0:1 and the layshaft spins at 5000 RPM and with the 17T the ratio will be lower (3.40:1) and it will spin faster, at ~5890 RPM converted to standard angular momentum units (radians/s) that's 618 for the 17T and 525 for the 20T.

Energy = 0.5 * I * w^2

if we call the inertia of the layshaft 10% larger with the 20T pulley than the 17T pulley, then the Energy stored in the assembly at 20000 RPM from the motor would be:

17T Energy = 0.5 * I * 618^2 = 190960*I

20T Energy = 0.5 * I * 1.1 * 525^2 = 151600*I

Here I is the inertia of the entire layshaft with the 17T pulley, and the assumption is that inertia is 10% higher with the 20T. If that assumption is true, then the energy "eaten" by the layshaft assembly is almost 25% less with the 20T. Again, that is a big assumption on the MOI difference between the two I have not measured the MOI on either pulley. One would assume that the % difference would be almost directly proportional to the difference in the square of the radius * the difference in mass of the two pulleys. If the actual iniertia of the two were plugged in, the result would be in units of Joules of energy.

Regardless what the inertias actually are, it's clear that the 20T will store less energy at high RPMs (where the sqaured angular velocity is dominant), yet the 17T will store less energy at lower speeds (where the larger moment of inertia on the 20T is dominant) The actual inertia or inertia ratio between the two will only tell you at what RPM the critical point is.

The result from this would be that the 17T should get up to speed a bit quicker, but become progressively more difficult to accelerate as the RPMs climb. The 20T will be slower initially, but past the critical point it will be able to accelerate faster. This is indeed what appears to be the dominant 'feeling'.

Keep in mind this is theory, and could all be totally negligible compared to the other effects. Just because the layshaft has more energy with the 17T pulley at high RPMs doesn't mean that energy is significant. It could easily be .001% of the total, but hopefully this can spark some more technical discussion at the very least.
Concillian is offline   Reply With Quote
Old 12-21-2002, 07:44 AM   #27
Tech Rookie
 
Join Date: Jan 2002
Posts: 9
Send a message via ICQ to Boy666racer Send a message via AIM to Boy666racer
Default

Interesting! - I like that idea, however, with the differences in weights and radi involved I dont think it will be possible to notice this difference!
Boy666racer is offline   Reply With Quote
Old 12-22-2002, 03:46 PM   #28
Tech Initiate
 
Join Date: Nov 2002
Location: SF Bay Area
Posts: 42
Default

You'd be surprised, as inertia is proportional to the square of the radius, the if one is a 15mm disc and the other a 20mm disc with no change in weight, the inertia of the 20mm disc is about double that of the 15mm object. Mass change would add another factor to this.
Concillian is offline   Reply With Quote
Old 12-22-2002, 09:21 PM   #29
Tech Regular
 
Join Date: Aug 2001
Location: Austin, Tx
Posts: 267
Default

Concillian...well posed argument...I think you may be on to something, especially in item 2, for a slightly different reason. Resistance to spinning (bearing friction) increases exponentially with rotation speed...therefore, if the layshaft with 20 t pulley is rotating at a slower rate, the friction resisting rotation is exponentially less than that for the 17 t pulley at the same car speed...combine this with the inertial effect, and you have what should be a noticable difference. I've been using the 20 t since right after I got the Mission, only using the smaller when I need it for really small tracks, but with the range of spur/pinion possibilities I have been able to make the 20 t work for almost everything.

Following the obvious, theoretically then a 24 t pulley should be better, but for any of you who have ever done any cycling, a small increase in the front gear makes a huge difference in gearing, and you have to stay within a reasonable gear ratio range, or you burn up your motor (or legs if riding)...

This makes much better technical sense to me than less belt bend...

my .02...later guys...Mark
markg is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale: TIR Mission Hinge Pin set & TIR Mission Titanium Screw Set NIP. Kraig R/C Items: For Sale/Trade 1 01-08-2008 11:41 AM
FS/FT :Mission Roller Hockey Inline Size 12 oceanhighz Other Items: For Sale/Trade or Wanted to Buy 1 01-03-2008 09:24 PM
xx4 pulley set raceGEEK R/C Items: Wanted to Buy 1 07-31-2007 10:53 PM
[SIZE=7]M11,M8,SPEKTRUM AND MORE[/SIZE][COLOR=Black] gonzo416 R/C Items: For Sale/Trade 0 10-12-2005 07:50 PM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 10:43 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net