syndr0me

iTrader: (32)

I'm genuinely interested in giving LiFe a try for something I'm experimenting with, but can't find one available anywhere. It looks like Reedy had something (a 4000) many years ago but that's about it.

howardcano

iTrader: (37)

Can you share with us what your experiment is?

Skiddins

This is the BRCA's approved LiFe list, last updated in February.
They had to be available commercially in the UK to be on the list, I *assume* they are still available.

http://www.brca.org/sites/www.brca.o...v1%20pdf_0.pdf

Skiddins

Found the Orion in the UK at a good price;
http://www.wheelspinmodels.co.uk/i/226344/

They seem to be almost all discontinued, so finding any might be difficult

syndr0me

iTrader: (32)

Sure, nothing exciting. I want to see how mod sedan feels with a LiFe. I like faster classes (love 13.5) but struggle with the rip of open mod. Trying to run flat LiPos and adjust ESC software hasn't yielded the feel I'm after. Considering trying a LiFe to see how that feels. I want something more dead in the infield while still fast on the straight and longer infield sections.

syndr0me

iTrader: (32)

You'll recall that the Europeans went to 5 cell once brushless mod hit the scene to make things easier to drive, and stayed competitive with 6 cell. I'm interested in trying something similar.

Skiddins

Have you tried a boosted 'mid' wind modified like a 7.5?
This was my 7.5, you can see it doesn't lack ponies on the straight but I was beig pretty cautious (first time on ETS style carpet)

+ YouTube Video

howardcano

iTrader: (37)

Sounds like a fun thing for a software guy to tinker with: tiny microprocessor reads throttle pulse from receiver, measures motor RPM via Hall sensors, uses look-up table to output new throttle pulse to ESC. Actually, I wouldn't be surprised if an ESC manufacturer has this already (though I haven't seen it).

You can also just run some long, light-gauge wires to the motor to add resistance. It doesn't take much.

P.S. Reducing battery voltage, using a higher-turn-count motor, adding resistance to wires, etc., may not change what you want: all of these still leave you with maximum torque at stall, tapering fairly linearly to zero torque at maximum RPM. To REALLY change the feel, you want to change the shape of the torque curve.

syndr0me

iTrader: (32)

Car looks reasonably powered for sure. That's such a nice, big open track compared to what we're running on here. I would think bigger motors might be easier to control with more space, but perhaps the opposite is true. Here's what we're running on right now for comparison: https://www.facebook.com/CORtrack/vi...7520841986103/.

I definitely haven't tried all the possible combinations of mild mod motors with boost, but I did experiment quite a bit with boosted 6.5 and found it was possible to calm things down somewhat through the ESC. I'm not sure if it's laziness or what, but I don't love tinkering with ESC settings as much as I probably should. I really like stock racing in that regard. Just set your drag brake and go.

The software part sounds interesting, but without an open hardware project that provides some sort of SDK, I'd be out of luck. There are some open ESC projects out there, but I don't think any of them are intended for sensored motors.

Some ESCs do a decent job of smoothing out throttle input, like the Orca. But of all the things I tried, undercharging my batteries (to about 8.0v) was by far the most effective and natural feeling. It's what got me thinking about reducing the voltage even further, and then maybe motoring up as needed. I suppose 1S could be an option, but that comes with the added hassle of powering your electronics somehow, and I don't know if there are any full-size 1S packs out there.

The thinner wires are an interesting idea. Does that added resistance cause the ESC to run hotter?

howardcano

iTrader: (37)

The hardware can be as simple as an 8-pin PIC. You only need to modify the control pulse width, and this can be done without ever touching the ESC. All of the software development tools are available free from Microchip, and device programmers are cheap. (You might prefer Atmel; I think all the same applies.)

Partially-charging the battery is a good, cheap way of reducing the power, and it's easy to change the charge level. There's nothing to buy!

Going to 1s with a lower-turn motor isn't going to solve the problem. The torque curve is still the same shape. But if you want to try, buy a saddle-pack and wire the cells in parallel. That's what I do on some of my loaner cars; I can run them all day without charging!

No, the ESC doesn't care. It just thinks there's a really sucky motor hanging out there. But again, this isn't going to feel much different than a partially-charged battery.

Many ESCs for brushed motors had a dedicated, hardware current limiter. This made a huge difference in the feel, since the torque curve was essentially flat all the up to a certain speed, like a kart with a slipper clutch. You can get this effect, and virtually any other torque curve you desire, via the software approach. But it ain't a small project!

Skiddins

I wouldn't rely on using thinner wiring to achieve an electrical solution. I've run open Mod in a 2s TC with 16awg wire and it still didn't get warm.

What about 10.5 or 13.5 boosted, at least you'd already have the 13.5's to play with?

syndr0me

iTrader: (32)

This is what I've been considering recently. It's possible I can get what I'm looking for by just adding some turbo on the straight.

Howard, I'm not sure how to change the torque curve of a motor. Less timing? Less powerful rotor?

Chris Adams

Charge your lipo to 8.00. Its got plenty of mah to handle it being charged less. Makes a pretty big difference.

syndr0me

iTrader: (32)

This has definitely been the most effective thing in the past. I was thinking LiFe would allow me to take it a few steps further without potentially damaging the battery. Something like a 4.5 or 5.5 at 6-7 volts sounds intriguing.

howardcano

iTrader: (37)

Other than dynamic timing, for a permanent-magnet DC motor there's no way to change the shape of the curve when at full-throttle. All you can do is change the slope of the curve. But it's still essentially linear, with maximum torque at zero speed and zero torque at full speed. And even dynamic timing only gives a modest change in the linearity; the torque is still maximum at zero speed, zero at full speed.

For DC motors with field coils, one can play all sorts of games. But we don't use those in RC.

The software approach lets one do fun things, like put maximum torque somewhere in the middle of the speed range (as for an internal-combustion engine). One could even put a little "kick" in the response, so a nitro guy would feel like his 2-speed transmission shifted.

Thanks for letting me ramble!