RC Crawler Differential Survey

[wings_of_fire]

Hi,

I have been busy for couple of days designing a 2.2 axle and differential system for my 2.2 crawler. I was thinking of designing a diff lock unlock system in it and would like to here from people their experience with such a system.

1] What kind of diff lock unlock would you prefer like manually actuated or electronically actuated.
2] What problems have you faced with such kind of diff systems?
3] Would it be a Go or No go to have a diff lock unlock system in your crawler ?

Looking forward to hear it all

[wings_of_fire]

Here is a link to a diff design similar to Venom that I modeled and was studying. Still working on my own design but need some inputs from you guys...
2.2 Crawler Differential - YouTube

[wings_of_fire]

looking at the number of replies I guess diff lock unlock system is not present in most of the rc crawler axles out there

[ROCKEDUP RICKY]

Originally Posted by wings_of_fire

Hi,

I have been busy for couple of days designing a 2.2 axle and differential system for my 2.2 crawler. I was thinking of designing a diff lock unlock system in it and would like to here from people their experience with such a system.

1] What kind of diff lock unlock would you prefer like manually actuated or electronically actuated.
2] What problems have you faced with such kind of diff systems?
3] Would it be a Go or No go to have a diff lock unlock system in your crawler ?

Looking forward to hear it all

I think it would be cool to have one. Manually would work , but electronically would be cool too. You would have to deal with a servo, maybe if it would work with a mico servo. I don't know of any diff like this. I think it would be a go to have diffs that you could lock and unlock.

[KJ10]

It could be useful but I would worry about how strong it would be. I've broken a couple dig units that were not the greatest quality or design. If you can build a bomb-proof one, that would be awesome!

And switching could probably be setup in such a way that you could do it manually or with a servo.

[AutoCrawler]

Cool project. Been thinking about the same thing. More from an engineering perspective than because its necessary.

I have a redcat Rs10XT. Its a 1/10 scale 2.2 MOA with rear steer and locked axles. Strangely there is a diff kit available for it so I got one just for fun. It's a traditional design with sun and planet gears. You can install a kit on both axles if you want since they are identical. There is no lock out. No instructions so I had to use a diagram I found from another redcat model to figure out how it goes together. Might install it tomorrow.

I haven't figured out how to lock both the left and the right axles to the the diff carrier/spur. Seems like I need a clutch type arrangement on both sides.

I don't do comps but my guess is that having a manual diff would be useful for some courses and probably an settable adjustable slip with lockout would be best since you don't wan the extra weight and complexity. You would set it up for the course appropriately.

For bashing or trail I think on the fly would be better and probably the limited slip would be too subtle to really make much difference although if you have it, then manually adjusting the slip seems reasonable. You would need a servo to control it but the servo should turn a worm gear or a cam and not be relied on to hold the diff locked/unlocked itself.

[wings_of_fire]

Originally Posted by ROCKEDUP RICKY

I think it would be cool to have one. Manually would work , but electronically would be cool too. You would have to deal with a servo, maybe if it would work with a mico servo. I don't know of any diff like this. I think it would be a go to have diffs that you could lock and unlock.

Points noted down. I was so eager to hear it from you guys.
Thanks a lot for your input ROCKEDUP RICKY.

Originally Posted by KJ10

It could be useful but I would worry about how strong it would be. I've broken a couple dig units that were not the greatest quality or design. If you can build a bomb-proof one, that would be awesome!

And switching could probably be setup in such a way that you could do it manually or with a servo.

Cool Points noted down. I am aware of the stress that the smallest pinion gear in the diff have to take. I have been having a lot of ideas flowing through my mind.

Thanks a lot for your input KJ10

Originally Posted by AutoCrawler

Cool project. Been thinking about the same thing. More from an engineering perspective than because its necessary.

I have a redcat Rs10XT. Its a 1/10 scale 2.2 MOA with rear steer and locked axles. Strangely there is a diff kit available for it so I got one just for fun. It's a traditional design with sun and planet gears. You can install a kit on both axles if you want since they are identical. There is no lock out. No instructions so I had to use a diagram I found from another redcat model to figure out how it goes together. Might install it tomorrow.

I haven't figured out how to lock both the left and the right axles to the the diff carrier/spur. Seems like I need a clutch type arrangement on both sides.

I don't do comps but my guess is that having a manual diff would be useful for some courses and probably an settable adjustable slip with lockout would be best since you don't wan the extra weight and complexity. You would set it up for the course appropriately.

For bashing or trail I think on the fly would be better and probably the limited slip would be too subtle to really make much difference although if you have it, then manually adjusting the slip seems reasonable. You would need a servo to control it but the servo should turn a worm gear or a cam and not be relied on to hold the diff locked/unlocked itself.

All points considered Limited Slip+Total lock unlock. I had not considered limited slip until your post but I like the idea of putting in all the available options in a single axle. With that will come a lot of technical problems to solve like you suggested - Complexity, Weight and reliability.

A friend of mine has a RedCat Rs10XT and is a fun crawler.
If you can, then please upload here some pics of the diff kit before you install it. I can put in my suggestions for it.

Thanks a lot for your input AutoCrawler.

[danmac]

What scale is this made for your talking about a lot of options in a small axle

[wings_of_fire]

Originally Posted by danmac

What scale is this made for your talking about a lot of options in a small axle

I will be making it for the 2.2 crawlers. I know they all seem to be a lot of options in a small axle, but I know I can design it. I have a lot of ideas in my mind and I am working on their design concept and development.

[Charlie-III]

WoF.....sounds like a great idea, I'm sure others will be waiting for your thoughts/ideas.

I will say.....sounds like a "fishing thread" which will likely get locked down since you're not a vendor here.

Not my concern, nor my rules.

I say this since I made an "off hand" comment about a part I had made for a local club member and had a few "moderator PM's" stating the same thing.

Not saying you should do different, just saying to expect a pm or 2 soon.

As to your question, most lock/unlock diffs I've seen thus far have been disabled since they are either:

Fussy & don't work all the time
Weak and tend to break

My son ran a Venom Creeper, among the 1st things he did (based on info here) was to disable the locking feature so it was always locked.

[wings_of_fire]

Originally Posted by Charlie-III

WoF.....sounds like a great idea, I'm sure others will be waiting for your thoughts/ideas.

I will say.....sounds like a "fishing thread" which will likely get locked down since you're not a vendor here.

Not my concern, nor my rules.

I say this since I made an "off hand" comment about a part I had made for a local club member and had a few "moderator PM's" stating the same thing.

Not saying you should do different, just saying to expect a pm or 2 soon.

As to your question, most lock/unlock diffs I've seen thus far have been disabled since they are either:

Fussy & don't work all the time
Weak and tend to break

My son ran a Venom Creeper, among the 1st things he did (based on info here) was to disable the locking feature so it was always locked.

I will get a blue star soon. and thanks for bringing it to my notice.
On the other hand calling it a fishing thread is pretty harsh.

regarding the differential guideline you provided, I am very Thankful to you

[Olle P]

The one type I'd really enjoy is the automatic unlock used on the rear axle of Volvo 903 (late '50ies design).
Normally locked, but if the wheels tried to run at different speeds (as when turning) it would unlock and stay so until both wheels ran at the same speed again.

[wings_of_fire]

Originally Posted by Olle P

The one type I'd really enjoy is the automatic unlock used on the rear axle of Volvo 903 (late '50ies design).
Normally locked, but if the wheels tried to run at different speeds (as when turning) it would unlock and stay so until both wheels ran at the same speed again.

Thanks Olle for your suggestion

In case you used the same diff in an rc crawler then it will not work while climbing rocks
It will be good if you are speeding on a flat surface and of course it will be good for 1:1 scale too.

[AutoCrawler]

Originally Posted by AutoCrawler

...
I haven't figured out how to lock both the left and the right axles to the the diff carrier/spur. Seems like I need a clutch type arrangement on both sides.

And I looked it up on u choob and it turns out that's one of the common ways its done in the real world. Give myself a gold star and put me at the top of the class

I took some pictures of the Redcat "open diff" but I didn't get around to installing it today. I may get around to posting them up this week. In the mean time it's very similar to this arrangement for a 1/8th scale differential.

http://redcatracingparts.net/image/c...3-900x900.jpeg

except it is driven by a spur gear rather than a ring gear and spur gear connects directly to the diff housing without the additional plates. Also it's not "hardened" and is smaller. The gears and pins are metal but the diff housing is plastic and the gears are cast not cut.

[Olle P]

Originally Posted by wings_of_fire

In case you used the same diff in an rc crawler then it will not work while climbing rocks.

Why not? I'm under the impression it would actually work better than having constant lock, since it wouldn't cause as much braking while running on uneven ground where the axles flex a lot back and forth.
As soon as a wheel slips the lock is engaged. (To disengage the lock some external force must try to make one, but not both, wheels run faster than powered by the drive shaft.)

[wings_of_fire]

Originally Posted by Olle P

The one type I'd really enjoy is the automatic unlock used on the rear axle of Volvo 903 (late '50ies design).
Normally locked, but if the wheels tried to run at different speeds (as when turning) it would unlock and stay so until both wheels ran at the same speed again.

Originally Posted by Olle P

Why not? I'm under the impression it would actually work better than having constant lock, since it wouldn't cause as much braking while running on uneven ground where the axles flex a lot back and forth.
As soon as a wheel slips the lock is engaged. (To disengage the lock some external force must try to make one, but not both, wheels run faster than powered by the drive shaft.)

Your last post information about differential and current post are in contradiction.
First you had said that the wheels would unlock if both wheels try to run at different speeds which is somewhat like a limited slip differential. Then in second post you said ...As a wheel slips the lock is engaged.

Can you please clearly explain.

[wings_of_fire]

Originally Posted by AutoCrawler

And Give myself a gold star and put me at the top of the class

I took some pictures of the Redcat "open diff" but I didn't get around to installing it today. I may get around to posting them up this week. In the mean time it's very similar to this arrangement for a 1/8th scale differential.

http://redcatracingparts.net/image/c...3-900x900.jpeg

except it is driven by a spur gear rather than a ring gear and spur gear connects directly to the diff housing without the additional plates. Also it's not "hardened" and is smaller. The gears and pins are metal but the diff housing is plastic and the gears are cast not cut.

cool
Yes the differential concept is same every where except the size, forces and other parameters change and hence some extra components increase or decrease where ever necessary.

I had worked for American Axle earlier. Not in the core R&D but I was working for a company that manufactured diff components for them. I remember setting up process to machine the inside sphere of the differential carrier and that job had to be very precise.

[Olle P]

Originally Posted by wings_of_fire

Can you please clearly explain.

I think the last sentence I wrote says it all: To disengage the lock some external force must try to make one, but not both, wheels run faster than powered by the drive shaft.

A driven wheel that slips doesn't try to outrun the driving axle, it just puts up less resistance.
The ground friction of the outer wheel in a turn does try to make it run faster than the inner wheel and driving axle.
The external force added causes the lock to disengage, and as soon as both wheels spin at the same speed again the lock is reengaged.

[AutoCrawler]

Originally Posted by Olle P

I think the last sentence I wrote says it all: To disengage the lock some external force must try to make one, but not both, wheels run faster than powered by the drive shaft.

A driven wheel that slips doesn't try to outrun the driving axle, it just puts up less resistance.
The ground friction of the outer wheel in a turn does try to make it run faster than the inner wheel and driving axle.
The external force added causes the lock to disengage, and as soon as both wheels spin at the same speed again the lock is reengaged.

Maybe I'm missing something but what you describe sounds exactly how an open diff behaves. The problem with open diffs is that since you cannot distinguish between turning and slipping you get the behavior where one wheel is spinning while the other is stopped. Locking the diff means you don't care about turning, just traction, so you can reduce slipping by combining the traction of both wheels all the time.

The problem with locking the diff is deciding when to unlock it. Since the wheels are locked together there will never be a difference in speed between those wheels to trigger the unlock. Generally practical modern real world systems unlock when the whole vehicle reaches a certain speed. This is largely a safety measure since a locked diff at speed will cause the vehicle to roll in a turn - avoiding this was why differentials were invented in the first place.

The solution to this is to use a limited slip differential. These act like they are locked until a large enough difference in traction between the wheels and the limited slip mechanism enables the differential to act thus allowing the wheels to turn at different speeds. When the traction difference is no longer sufficient then the wheels again act like they are locked. The limited slip diff is never really fully locked since it's not as binary as my simplified description implies.

Perhaps this is what you mean?

[Olle P]

Originally Posted by AutoCrawler

Maybe I'm missing something but what you describe sounds exactly how an open diff behaves. ...

Definitely not!
With an open diff if a wheel slips more power is transfered to that wheel, making it spin faster.
No additional external force is involved!

This diff is locked by default, so if a wheel slips more power is transfered to the wheel that has grip, and both wheels keep spinning at the same speed.
To unlock it an external force must add speed to one wheel only. (Reduced traction doesn't force a wheel to spin!)

What's good about it is that when there's grip it behaves as if open, but when the grip is lost on one or both wheels it stays locked.