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Basic car radio questions

Old 03-18-2008, 02:25 PM
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pwood
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Default Basic car radio questions

Hi Guys

I have been toying with the idea of getting a 1/8th Buggy. I have been flying planes for the last 25 years and helis for the last 6 years.
I am a little confused with some of the radio functions on the car radios. So help please....

I have been doing some research on the Spectrum DX3R and the Futaba 3PM Fasst. They both seem good. I am not intending to do a shoot out, just ask some basic questions.

Both radios have ual rate (steering rate), is it like an aircraft radio, ie a toggle switch with a 2 pre-selected steering % OR is it like a trim button to progresivily increase and decrease the steering % as you are driving. Is this just done by feel?

Both have: Throttle and Brake trim. Trim usually moves the centre point of the servo, so why two trims on the one channel? I guess the brake trim is actually the brake end point to change the max brake setting while you are driving. Why do you need a throttle trim? surely the carb idle stop screw needs to be set for an accurate idle. a radio trim setting would just be over ridden as soon as you brake?

The DX3R has: Dual rate 9steering rate) overide, what is it? Push the button and get a pre-selected steering % while you hold the button? ie overiding the previous dual rate setting?

The 3PM has: ABS brakes. the instructions explane it well, but is in necessary on an off-road buggy?

The 3PM has: Steering delay. We spend more and more on fast servos, So why a delay function? is it necessary? If it is to stop jerky steering, would steering expo not do the job?

The 3PM has : Throttle delay. What for? to stop wheel spins?

The DX3R has: Steering servo frame rate setting. Why only on the steering? Does this meen the 3PM can not take advantage of the super fast servos at all?

I hope you guys can help me out, thay may seem like real dumb questions for a car guy....but for a heli guy......

Regards
Paul





Old 03-21-2008, 08:42 AM
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Sean C
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Default RE: Basic car radio questions

Hi,

I'll try to answer some of your questions...

Dual rates: You pretty much guessed it. Typically, you'll set up your endpoints w/ dual rates at 100%. You'll keep it at max for tight tracks and lower it for larger, faster tracks... and it comes down to feel and preference.

Throttle & Brake trim: This is new to me... I've never used this so I can't help ya here. Usually, ATL is used to control the endpoints on either side of neutral "on the fly" - much like the steering D/R.

DX3R d/r override - no idea, but sounds like you may have it right.

ABS Brakes - Neat idea, would probably work best for on-road applications. If you're locking up your wheels on dirt, mechanical adjustments would likely be more beneficial.

ST/TH Delay - With today's high-speed digital servos, sometimes you do need to slow down the servos... high speed steering servos can make the vehicle too squirrely for some drivers and high speed throttle servos can in some cases cause the engine to stall out when opening the throttle too fast. Expo might help - it's personal preference.

Frame rate: Analog servos cannot handle the same frame rates that digitals can. Futaba uses "HRS mode" for a higher frame rate, but ALL servos must be digital - whereas the Spektrum, from what I understand, will allow you to mix analog and digitals while optimizing frame rates for the digital.

On throttle/brakes digital servos are becoming more popular because of holding power (brakes), not necessarily speed.

I hope this was helpful... maybe some DX3R owners can chime in and better answer the spektrum-specific questions [8D]
Old 03-21-2008, 02:49 PM
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pwood
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Default RE: Basic car radio questions

Hi,
Thanks for the answers. Just to clear things up....please be patient.
On an off road buggy, do you set up the brakes NOT to lock up the wheels, even at max brake?
The steering dual rate, is it like a trim switch that you can increase and decrease the current available rate while you are driving and not like an aircraft where you click a 2 possition toggle switch from one pre programed value to another. (usually 100% and something less....like 80 or 70%)

Thanks again
Paul
Old 03-21-2008, 05:43 PM
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Default RE: Basic car radio questions


ORIGINAL: pwood


On an off road buggy, do you set up the brakes NOT to lock up the wheels, even at max brake?
This will most likely depend on user preference and the type of surface you're running on. On high grip surfaces it may be beneficial to have the wheels lock up (or almost) under full break, whereas if running on gravel full brake would most likely send you sliding off the track!

The steering dual rate, is it like a trim switch that you can increase and decrease the current available rate while you are driving and not like an aircraft where you click a 2 possition toggle switch from one pre programed value to another. (usually 100% and something less....like 80 or 70%)
Generally an exact rate can be selected, with an override to return 100%.
Old 03-21-2008, 11:23 PM
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Sean C
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Default RE: Basic car radio questions

pwood,

lock-up under braking is a personal preference and depends on the track as snowblind pointed out. The point I was trying to make was that if you need the ABS feature then you're using the radio to overcome a mechanical adjustment... which is fine - its up to the individual. Furthermore, I would think that the brake pulsing would be tougher on the drivetrain.

The steering d/r on most surface radios is usually set to a rotary/button trim or , unlike the toggle switch on our aircraft radios. My 3PK has two rotary trims next to the trigger - one for d/r and one for atl. With this I can tune my car to the track and conditions while driving and w/o altering any other programming.
Old 03-22-2008, 01:37 AM
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pwood
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Default RE: Basic car radio questions

Hi guys

I think i get it.

Thanks
Paul
Old 03-23-2008, 05:02 PM
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trarena
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Default RE: Basic car radio questions


ORIGINAL: pwood

Hi guys

I think i get it.

Thanks
Paul
Just a quick comment on the ABS feature... this will result in a rapid engage/disengage or pulsing brake action which IMO puts undue strain on the servo (and possibly the drive train). If you were worried about brake lock on a loose surface better to adjust brake tension instead.

And in my not so unbiased opinion I would suggest the DX3R!
Old 03-24-2008, 12:49 PM
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pwood
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Default RE: Basic car radio questions

Hi Trarena

I am very biased towards the DX3R. I am a real Spektrum suporter. I have a DX7 and DSX9. I do not miss my Futaba 14mz at all.....

The Futaba 3PM is packed with features and is cheaper, but i just like the DX3R.

The things that are 'missing' from the DX3R that are on the 3PM are ABS brakes, Stearing delay and Throttle acceleration.

Are these a big issue for off road buggies?

Thanks again
Paul
Old 03-25-2008, 04:56 AM
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Default RE: Basic car radio questions


ORIGINAL: pwood

Hi Trarena

I am very biased towards the DX3R. I am a real Spektrum suporter. I have a DX7 and DSX9. I do not miss my Futaba 14mz at all.....

The Futaba 3PM is packed with features and is cheaper, but i just like the DX3R.

The things that are 'missing' from the DX3R that are on the 3PM are ABS brakes, Stearing delay and Throttle acceleration.

Are these a big issue for off road buggies?

Thanks again
Paul
Hi Paul

IMHO

1. you do not need those 'missing' features at all (nor do i need a back light feature - i do not race under floodlights and to be honest, i don't look at my display when i am racing - except maybe the timer for fuel stops).

2. the lightness and speed of the DX3R far outweighs any shortfalls it may have.
Old 03-31-2008, 03:19 PM
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Default RE: Basic car radio questions

Paul buddy!! I see you're quite serious about joining us in Nad for the buggy races

I just want to answer one of your first questions (the other members covered the rest)..."why u need a throttle trim...??" The main reason is to open the carb a bit to help in starting the engne, just like a choke lever on older fullsize cars with carbs. Once the engine starts you can bring back the trim down. This makes starting easier by not having to keep a finger blipping the throttle trigger and trying to start the car and hold the glow igniter all at once. Another use, for me at least, is sometimes a take the trim below neutral so as to have the brakes apply lightly when I release my finger of the trigger...this helped me when I was starting the hobby and was trying to control the speeds these beasts reach.

I'd also like to add a thought about the ABS: the reason cars have ABS is actually mainly to improve/maintain steering while braking. In buggies this isn't as necessary as onroad since offroad driving style is very different from onroad...if you watch rally driving you see power-sliding is a big part of steering .

see u next weekend buddy!

Rawad

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