Differentials?

Tips and tricks about building a car. painting it a making it run smooth.
Post Reply
acboother
Posts: 17
Joined: Wed 25. Oct 2017 07:27

Differentials?

Post by acboother »

Speaking as someone who still has to get a car running on a track...

I am going my own way on the design and build because... well just because. I have done some simple tests and getting the car to turn it at the corners seems to me to be an essential part of getting a nice handling car.

Grippiness of the tyres seems to be desirable in all aspects except one and that is without a differential on the rear driving wheels the car will have tendency to be driven straight on when the front wheels have a preference to be turning the car.

Has anyone thought about using a differential? Available in the little RC cars are differentials that look like they could be made to fit. Two motors and a split axle, magnetically coupled split axle (??!!), something else.

Obviously it can be made to work without a diff, as I can witness cars speeding around a circuit, but is this done with compromises on grip which, if they didn't have to be made, could result in a car that goes faster, brakes harder, steers better?

Cheers Alan
kiklo
Administrator
Posts: 485
Joined: Mon 9. Nov 2015 11:49
Location: Norway
Contact:

Re: Differentials?

Post by kiklo »

Grip is dual sided sword for us.

Primary goal with Magracing was to get a scale-like handling.

That to make it challenging to run at scale speed. To good grip will ruin the challenge.
So there are really no need for or request for super grip.

So some slip makes a differential unnecessary complicated and not needed.

In fact personally I'm testing chassis with some flex to achieve the wanted slip on inside rear wheel.
Racing Regards

Kim K.
acboother
Posts: 17
Joined: Wed 25. Oct 2017 07:27

Re: Differentials?

Post by acboother »

I'll pursue the differential route for a bit. Complexity is not an issue for me as playing about is what/why I'm doing this. I have three different ones already to choose from plus the possibility of the dual motor option. It's all good experimentation as I need nearly all these problems solved for my LIDAR car which 'sees' the track walls in order to work out where the track goes.

If you want to assist styre slipping differential behaviour you must adjust the loading on rear wheels, inside to outside. This has tendency to happen anyway because of weight transfer during cornering (provided that the CoG is above the track level - which of course it always is) puts more traction onto the outside wheel.

What is your thinking behind a flexible chassis to aid the load/weight transfer and change the slip'ability of the tyres?
kiklo
Administrator
Posts: 485
Joined: Mon 9. Nov 2015 11:49
Location: Norway
Contact:

Re: Differentials?

Post by kiklo »

Yes without being very scientific, some flex in the chassis will allow for some twist and less jumping behavior on uneven surfaces - I think.
Given the body are not restraining it.
The 3 point magnetic fixture for the body is also beneficial in so way. Kudos to Wes.
Racing Regards

Kim K.
acboother
Posts: 17
Joined: Wed 25. Oct 2017 07:27

Re: Differentials?

Post by acboother »

I can see the flex will aid dealing with uneven surfaces.

I think if you want more 'differential' effect due to weight transfer, raising the CoG at the rear of the car (especially if you are building in flex) will do that.

If the extra flex doesn't already give you want you need (it all depends upon how the weight transfer occurs between front and rear as well - not just left and right during a corner). Just imagine the CoG so high that the car was just about to lift the inner wheel on a corner... you would have total slip on that wheel. Obviously not something you would do in practice as other undesirable side effects would kick in!
WesR
Posts: 371
Joined: Fri 21. Dec 2012 17:37

Re: Differentials?

Post by WesR »

I have several times tried removing the front centre magnet to reduce the stiffness added to the chassis by this method of body fixing, most successful being the use of a horizontal pin at the front of the chassis. This does need more care when removing the body however and, since adding the front suspension to all my cars, I have gone back to a small magnet with a short vertical pin to hold the body after a severe shunt! The front suspension adds nothing to the cost and is here to stay as far as I am concerned. I can't say that the suspension transforms the cars but it does allow a more rigid body fixing and it does compensate for any small twist in the chassis.
I have never thought much about a differential. I guess it would make lane changing easier but then again, the cars might be less inclined to run straight through the lane change, on the default straight on route. At least we know where we are with the fixed axle. There is a lot to think about now and not sure that we need any further complications.
acboother
Posts: 17
Joined: Wed 25. Oct 2017 07:27

Re: Differentials?

Post by acboother »

I'm happy to fiddle with the 'complications' as I have no intention of going into production and failure and wasted effort are all part of it for me.

I'm still thinking about two small motors, one for each rear wheel. One of my LIDAR cars had this and I was going to make them independently controlled so they could assist the turn (rather than fight it) as in differential steering on line following cars.

Onwards and upwards with the ideas... or sideways or even downwards but just keep on moving.
Post Reply