BL FWD & Petrol RWD.? - RC-Monster Forums

aqwut · **BL FWD & Petrol RWD.? -** 12.18.2007, 06:22 PM

I took out the Firehammer M/T out earlier today... and it really sucks with 2WD... I took a close look at the front of the M/T.. and inbetween the shock tower and chassis is a big open space... I was thinking... maybe using an Outrunner as a Differential.... or maybe put a Differential and directly attach the outrunner on to it..... it wouldn't take much to make it work.... but 2WD drive just really sucks monkey butt....

suicideneil · 12.18.2007, 06:28 PM

How would you match the speed of the BL motor to the revs of the petrol engine? Sounds more like you want to install another diff and driveshafts in the front of the truck to make it 4wd, like people did with the Wheelieking before HPI released the 4wd version....

aqwut · 12.18.2007, 06:42 PM

I would just gear it a little bit faster than the rear... I'll figure it out somehow... :) it's gonna be hard to match the rear speed... I'll just make it go faster.... LOL, hopefully nothing will happen... Have anyone ever tried something like this before... because the 4WD kit for the FG marder is way too expensive to buy...

BrianG · 12.18.2007, 06:48 PM

Hmmm, an rpm sensor on the rear shaft/diff feeding a voltage-controlled oscillator that outputs 1ms to 2ms pulses at 50-60Hz to the ESC in proportion to the speed. Just a thought...

aqwut · 12.18.2007, 06:52 PM

Quote:

Originally Posted by BrianG

Hmmm, an rpm sensor on the rear shaft/diff feeding a voltage-controlled oscillator that outputs 1ms to 2ms pulses at 50-60Hz to the ESC in proportion to the speed. Just a thought...

what kind of stuff would I need for that... it would be awesome, but probably too difficult for me...

suicideneil · 12.18.2007, 06:59 PM

I think Brian just blinded me with science! Generally though if the rear of a vehicle tried to go faster or slower than the front, it leads to erractic handling and spin outs, so I would say you be a bit buggered really in that department. Would a bigger engine make it more fun to drive?...

aqwut · 12.18.2007, 07:02 PM

it's just no traction on the rear.. get's stuck all the time, I had a lot of exercise... that's not good... LOL I saw ones with 30.5 engines, and they fly.. but I like the 4WD.. I just thought it might be cool to have Petrol and Brushless working together.... I'll figure something out... BrianG.. if you hook me up with all the info I need to make this magic sensor happen... it would be a nice winter project...

BrianG · 12.18.2007, 08:04 PM

lol, it was just a quick thought. That's not something I can just whip up - it would take some testing and tweaking. On second thought, I'd probably use the RPM sensor hooked to a 555 timer (oscillator) in monostable mode and play with the cap and resistor values to see if I could get a the proper output signal the ESC wants to see. I built a servo tester a while back, and this would be somewhat the same, except use the rpms of the rear end as the control instead of my fingers turning a pot.

Even then, I think you'd have issues trying to match up the power levels. The power starts out small and increases with rpm in a gas engine, while BL is the opposite. It would be kinda weird to have understeer at low speed (high front-end pull from the BL) and some oversteer at high speeds (more HP from the gas engine) - kinda backwards from the norm.

Honestly, I would think it would be easier to devise a mechanical link between the front and rear instead of rigging something like this. Would be interesting though.

ilpufxit · **Helis -** 12.18.2007, 08:19 PM

The tail rotor on a small electric heli is electronically regulated in proportion to the main blade. Its called a 3 in 1 and its easy to adapt a brushless controller. I'm not really an electronics guy but there should be a way to use the same type of control.

aqwut · 12.18.2007, 10:21 PM

cool.. I"m just gonna go for trial and error.... :) until I figure something out... I'll come up with something... thanks guys...