Motor choice for 2wd= fast, or slower + boost

[colmo]

I've added a comparison to the spreadsheet of a non-boosted Ballistic 7.5T to a boosted 10.5T, using the same assumption of 1% Kv gain per degree timing.

The result is while the RPM range of the 7.5 is linear, the 10.5T is not - comparatively, it initially yields less RPMs at lower voltage, but more at higher voltage - the Kv ramps up steadily through the range as the timing is advanced more and more.

The effect is much like a little negative expo on the throttle, which would give a boosted motor a 'softer' feel, of less punch, yet excellent top speed.

Link to Google Doc again: https://docs.google.com/spreadsheet/...V9hQ1JZTVlDbFE

[Timee80]

This is what I was talking about. Finally someone understands me!

[colmo]

One other thing to keep in mind - of the 60 degree additional timing you can boost by, you must include mechanical timing of the motor. Most motors have some dialled in automatically and some can be adjusted too. The old Speed Passion (Feigao-made) motors have a fair amount of timing dialled in, and I recall the LRP/Nosram x11 had quite a lot. It appears that 30 degrees is the normal 'zero' for brushless motors - they don't perform well with less.

The touring car guys, who know more about this than off-roaders, know the Speed Passion v3 and GM motors have zero timing set mechanically. I'm not sure what other motors do too.

Note that the Ballistic motors have 30 degrees of timing as standard (the usual), so the additional 60 degrees of boost timing aren't actually attainable. I'll recalculate to add only 30 degrees boost timing - see below.

[James]

I did a fair amount of testing between different winds/boost etc.. Came to the conclusion just to stick with a 7.5 or 8.5 in 2wd with no or very little boost.

[colmo]

It seems the norm for boosted brushless setups are 30 degrees mechanical timing, and up to 30 of boost plus turbo.

See the Hobbywing Xtreme Stock manual (which states true degrees of timing), giving 21 degrees of boost, plus a further 8 of turbo, for a total of 29:

http://www.hobbywing.com/upload/manual/HW-09-XST.pdf

In a situation where there's no motor limit, the greater efficiency of a lower wind motor and no ESC trickery, plus the simplicity of setup, makes boosted motors seem unnecessary. If traction is low, dial in some negative expo or lower the punch setting on the ESC.

The one advantage of boost is adjusting for different tracks without changing motor - just leave your gearing alone (set for technical tracks), and dial in some boost to give the car the legs on the longer straights of a bigger track.

[stumpiey]

iv ran a turbo'd 10.5 and a non turbo 6.5, on bigger outdoor tracks i would use my LRPx12 6.5t but indoors it's to much so i use a 10.5 which i feel a bit is better for my driving, plus coming from TC i understand how to get some real ponies out of a 10.5 set up

[ianjoyner]

Originally Posted by James

I did a fair amount of testing between different winds/boost etc.. Came to the conclusion just to stick with a 7.5 or 8.5 in 2wd with no or very little boost.

How come?

[colmo]

Originally Posted by Gayo

I agree with that. Last sunday I had a race indoors (slippy wooden floor and carpet) and instead of my usual 7.5, I used a 10.5 with dynamic timing.
While top end was the same (maybe even faster with the boosted 10.5), I felt I had less low-end torque, which was good on the wooden floor but Iwas lacking a bit of grunt on the first half of the carpeted straight.

So for me it will be 7.5 on carpet and astro, and boosted 10.5 on low grip conditions

My comparison of the Ballistic 10.5 with 30 degrees of dynamic timing boost to the 7.5 without supports this (limited as it is with massive guesstimaton!); similar top end, with the mod motor giving more mid-range.

I'm wondering if dialing in positive expo on the throttle would 'flatten' the curve and give more punch?

[TARTMAN]

so technical...

I am oldschool style. fast motor, sort the grearing and use the throttle thumb to sort it....

works for me.............

wil prob try the new stuff soon, but only been back in it since sept this year after 22 years out..... so early days...............

Originally Posted by colmo

My comparison of the Ballistic 10.5 with 30 degrees of dynamic timing boost to the 7.5 without supports this (limited as it is with massive guesstimaton!); similar top end, with the mod motor giving more mid-range.

I'm wondering if dialing in positive expo on the throttle would 'flatten' the curve and give more punch?

[Timee80]

It would be nice to have one motor you could use on all tracks in all conditions, achieved by simply changing punch / boost + turbo timing. I think a 10.5 would be about perfect once people more knowledgable than me have fully sorted the programming side of things. Ive tried a 13.5t boosted in 2wd too but I had to use alot of timing to gain enough from the motor which made acceleration feel "funny"- I dont know how to describe it really.
I think the strange feeling comes from when the buggy is in the air/landing because rpm's are all over the place.
The yanks may know better than us because theyve been using slower motors for ever?

[samd]

I'm not sure this means anything with just assuming a certain kv raise per deg off boost.
Also the esc dosent vary voltage, it's constant, motor speed is determined by the + - wave, and boost timing speedos add timing to motor rpm not running voltage.

I think

Originally Posted by colmo

I've added a comparison to the spreadsheet of a non-boosted Ballistic 7.5T to a boosted 10.5T, using the same assumption of 1% Kv gain per degree timing.

The result is while the RPM range of the 7.5 is linear, the 10.5T is not - comparatively, it initially yields less RPMs at lower voltage, but more at higher voltage - the Kv ramps up steadily through the range as the timing is advanced more and more.

The effect is much like a little negative expo on the throttle, which would give a boosted motor a 'softer' feel, of less punch, yet excellent top speed.

Link to Google Doc again: https://docs.google.com/spreadsheet/...V9hQ1JZTVlDbFE

[lochness42]

I didn't like supercharger/turbo in TCs. It used to upset car when it kicked in.

[TARTMAN]

I find in the 2wd, when the turbo kicked in on the strait it was a little unsettling and just meant harder braking and that unsettled it again.

I will stick to no turbo and a madder motor.... also, i think that a turbo'd/timed motor will get hotter than a mad one just doing its thing...
Might be wrong on that thou..........???? Answers on a post(card) please lol...

Originally Posted by lochness42

I didn't like supercharger/turbo in TCs. It used to upset car when it kicked in.

[Timee80]

Originally Posted by lochness42

I didn't like supercharger/turbo in TCs. It used to upset car when it kicked in.

Surely that depends on how much timing advance is used and how aggressive it is set up?

[Timee80]

Agreed, a milder motor will get hotter when turbo settings are used but its a small price to pay if you can use one motor everywhere and have a buggy that is more driveable at lower speeds. I tend to get nervous on the rostrum (especially if doing well) and having to tickle the throttle with a quick motor to get the right speeds in the infield becomes harder when your shaking like a sh!tting dog

[h0m3sy]

Originally Posted by Timee80

Agreed, a milder motor will get hotter when turbo settings are used but its a small price to pay if you can use one motor everywhere and have a buggy that is more driveable at lower speeds. I tend to get nervous on the rostrum (especially if doing well) and having to tickle the throttle with a quick motor to get the right speeds in the infield becomes harder when your shaking like a sh!tting dog

[colmo]

Originally Posted by samd

I'm not sure this means anything with just assuming a certain kv raise per deg off boost.
Also the esc dosent vary voltage, it's constant, motor speed is determined by the + - wave, and boost timing speedos add timing to motor rpm not running voltage.

I think

Oops, yes, you're right. Brushed ESCs do vary voltage, brushless vary pulse frequencies, so voltage in this case is nonsensical. I'll change the X axis to percentage of maximum power, as I can't think of anything else to put there that means anything!

[jaywestwood]

Originally Posted by lochness42

I didn't like supercharger/turbo in TCs. It used to upset car when it kicked in.

Change the turbo delay up.. 10.5 with generation 3 speedo is faster than a non boosted 7.5 motor.. If you also turn the start rpm up it will be smoother of corners and will only kick in when your ready for it

[guinness]

in my trf201 i been running a 6.5t pure evolution together with a stock no timing esc for a wile,and i must say that that motor was to much to handle,then i swapped to a 10.5t lrp vector x11 and my times improved big time but not really enough quick/torque in the straight ,so now i just fitted a 8.5t bullistorm and i will race with it this coming friday ,i hope this would be a good middle ground.

[RogerM]

In offroad I have found that using very little normal dynamic timing but lots of "turbo" timing, with very slow rates of timing rise and the lowest possible start RPM gives a car that is lovely and smooth to drive and just as fast as it would be on a faster motor.

As has been said previously be careful of the mechanical timing on the motor and make sure you keep the total timing to sub 60deg (I use 58deg as my peak value, just in case I am a fraction off on the mechanical timing).