What transmitter would be most capable for exotic mixes to work with a DIY 'on the fly' variable centre differential?

[Ari33]

I'm thinking of attempting to use a nitro centre diff with the twin brake discs on either side of the diff on an ebuggy..... Not only to have adjustable F/R brake balance but also to be controlled by seperate servos to allow me to be able to adjust the centre diffs torque split 'on the fly' and also with some clever radio mixes to give me variable torque splits for braking/acceleration/ steering combinations with seperate gain pots for each..

What tx would have the widest range of mix options and adjustability of whats currently on the market?

 

[LibertyMKiii]

Subscribing for more info. I have seen a single servo control mechanical brakes, but what you are describing would be significantly more complicated. While I don't know the answer to your question I would assume it is likely going to be the Futaba 7PX

-Liberty

 

[Ari33]

Subscribing for more info. I have seen a single servo control mechanical brakes, but what you are describing would be significantly more complicated. While I don't know the answer to your question I would assume it is likely going to be the Futaba 7PX

-Liberty

Thanks.

It could definately be done in Opentx on my Taranis using global variables or special functions so I might try and use that if I don't get a definitive answer with regards to wheel/trigger type Tx's which seem pretty basic in comparison.

This is just a simple example but the possibilities are huge, they can be do so much more -

My ultimate aim is to create a model that can be made to handle somewhat like a WRC car. In that the diff can be variably opened or closed for any throttle/brake/steering combo via the programming on the radio as drive by wire/gyro/accelerometer in the car isnt legal in racing.

What we have just now is basically a mid engined audi quattro, it can be tuned to react in a certain way but is limited by a set centre diff. When that can be opened or closed you can see from the modern WRC cars how superior it could be.


Perhaps a cruder version of an active centre diff would have to be on the tx side where steering would variably open the diff, brake or throttle would variably lock it... but I'd like to have the gains adjustable seperately...
I'd also like to fit 2 pressure sensitive micro switches into the handle with each either increasing or decreasing the overall gains depending on it being a fast or slow track section for instant stability or agility modes under my fingertips.

 

[nino]

Have you looked into hacked flysky FS GT3's mixing options?

 

[Ari33]

Have you looked into hacked flysky FS GT3's mixing options?

Not yet, but I'll have a look now. Cheers for the tip..

 

[SrC]

Old thread...
If your into programming like you are describing, don't rule out two programable servos to meet your objective. And most premium 6+ chanel radios will work for you.

 

[Ari33]

Old thread...
If your into programming like you are describing, don't rule out two programable servos to meet your objective. And most premium 6+ chanel radios will work for you.

I hadn't really thought that far ahead tbh... but I really love that solution. Very neat idea.

 

[Yonic]

I like this direction, but I’m not sure solving it from the TX side is possible. Let’s say you’re driving the car at 80% speed, so your throttle is at 80%, but the drivetrain is actually at neutral, therefor you want the diffs to be open, but your solution will lock it.

 

[Ari33]

I like this direction, but I’m not sure solving it from the TX side is possible. Let’s say you’re driving the car at 80% speed, so your throttle is at 80%, but the drivetrain is actually at neutral, therefor you want the diffs to be open, but your solution will lock it.

I'm planning on using F&R brakes on seperate channels to act as a crude and inferior form of an active centre differential. Electro magnetic clutches would be superior in every way. I just haven't come across a suitable clutch that could be retrofitted very easily.

Anyone remember Prodrives V2 concept car?

Its active centre diff was the only active diff system that made the Stig over 4 seconds faster per lap when activated on the Top gear test track.

I don't like the cars styling but its pretty interesting from a technical viewpoint.

 

[SrC]

I like this direction, but I’m not sure solving it from the TX side is possible. Let’s say you’re driving the car at 80% speed, so your throttle is at 80%, but the drivetrain is actually at neutral, therefor you want the diffs to be open, but your solution will lock it.

That's where programable servos might offer a solution.

 

[Ari33]

This guys (silly IMO) use of outrunners inside the wheels (which would clearly have a lot of its own obvious issues... never mind being seriously underpowered!)

... got me wondering about attaching small brushless outrunners on either side of the centre diff.... Or.... even the front and rear diffs... to able to accelerate or brake individual wheels.

The car would still be powered by a single big motor but in theory the torque split could be varied not only from front to rear... but also side to side for a fully active car.
If the motors were also sensored, the possibilities further grow... and exponentially... with proper traction control and proper 4 channel ABS being achievable in theory.... if I was good a coding. :/

No more fixed handling with the set diff oil viscosities.. they could be filled with a very light fluid and the diff drive/torque transfer controlled by the outrunners instead.


Quad motors escs are very light, tiny and dirt cheap. I'm just having a hard time imagining how powerful they would have to be and what percentage of drive and grip torque they would have to cope with though?




Its just one of my many engineering thought exercises... but it would interesting to hear peoples thoughts.

 

[Yonic]

I thought that instead of one big motor, you could have 4 smaller motors (1/4 in size), 2 on each axle (where the front/rear diffs are), so diff won't be needed, each motor will be directly connected to corresponded wheel (via some gearing of course). the ESC will distribute the power based on the steering, so when you're going straight all the motors will spin at the same speed, but if you turn each motor will turn at the precise speed it needs to comply to the turn, so you won't have (or need) diffs and the power split will be perfect on every condition.

A gyro could also be incorporated, not to counter-steer for you (as it is used on AVC systems and such) but to maintain the proper power split when you're over/under steering

 

[Ari33]

I thought that instead of one big motor, you could have 4 smaller motors (1/4 in size), 2 on each axle (where the front/rear diffs are), so diff won't be needed, each motor will be directly connected to corresponded wheel. the ESC will distribute the power based on the steering, so when you're going straight all the motors will spin at the same speed, but if you turn each motor will turn at the precise speed it needs to comply to the turn, so you won't have diffs and the power split will be perfect on every condition.

Thanks for your input..
That was my natural and initial thought... and on researching it I found that exactly that approach had been done as part of someones school engineering project.



https://hackaday.com/2014/07/12/independent-wheel-drive-rc-car/

and

https://www.reddit.com/r/electronics/comments/2aaccd

Its certainly an interesting read!



My issues with it are..

Developing and coding an indepedant wheel drive system.. that relied on wheel position information to create a faux balanced drive with no actual mechanical linkage would be a far larger task than I am capable of at this time in my life. Coding is definately not my forte. ?

At least with a mechanical 4wd system you would find it a lot easier to find a good neutral mechanical drive balance and just tweak it electromechanically... and I might be capable of achieving it with good results?

 

[razorrc]

Check out the Futaba 4PM manual at the futabausa.com site, it's got a lot of mixing modes for various things (4WS, dual ESC/motor, gyros, etc.). It seems pretty exotic/capable to me. You can also program the switches and dial to control the mixes in real-time. Not too expensive at $230 for a high-quality radio.

https://futabausa.com/wp-content/uploads/2019/07/4pm-e.pdf

Here's my review of the radio (no review of the mixing because I don't use it) from more of a bash/race background.

 

[Yonic]

I found that exactly that approach had been done as part of someones school engineering project.

That's truly amazing! and exactly what i imagined. nice find.

I just cannot imagine this not being the future.