motor in wheel concept?

[fennex]

Has anyone tried to build a crawler with 4 small BL motors inside the wheels, and 4 ESCs?
If all motors and ESCs are the same, the wheels would all rotate roughly at the same speed.
So no need for any transmission, differential, shaft etc.

The problem would be to find a motor and some sort of reducer that fit inside the hub. The rims will probably have to be either machined to suit or custom made.

There are many research papers on how to control wheel speed depending on the steering angle, so the electronically simulated differential would not be too hard to add if wanted.

Any suggestions for this concept?

[Jer]

It sounds like an interesting idea. I don't know how you could get the gear ratio correct and fit inside a wheel though, maybe if you ran super wheels.

[asw27x]

that seems like a good idea but only for super class i have already been thinking about it i think i will build that when i do a super class

[JohnRobHolmes]

It is possible for sure. I have designed a few motor wheels for the purpose, but haven't executed any designs yet. A simple way to make a super would be to use an existing motor wheel available for electric bikes.


Probably the most feasible for a custom design would be using a 24 slot 28 pole "outrunner" design with a floating ring and planetaries. The ring (driver) could run a set of fixed planetaries that drive the rim (driven) for decent geardown and plenty of grunt. Floating planetaries could allow for a different gear ratio as well, so making it a two speed design is pretty easy.

For a semi custom design, a two or three stage reduction unit could be fabbed that mounted to a hub and fit inside a wheel. Probably most feasable for a super. I designed one in 2005. Still have the parts, just ended up using motor on axle design instead.


The downfall is the large unsprung weight and the poor power to weight ratio. As you remove reduction, the motor must become larger to sustain the torque. Fine for a robot or lunar rover. Piss poor for a competitive crawler.

[miller10]

That would be sweet as hell, but it seems like its over-engineering a pretty simple and effective design as it currently is...hell build it and be a pioneer everyone can be jealous of!

[Jeepkid]

It will need a trans, that is how you get your gear reduction. Otherwise it would stall in a bind. Great idea though for a super, 2.2 you would have to watch your wieght.

[CheapTwin]

I've thought about this for a long time and i was wondering if you could use 4 pcs. modified high torque brushless sevos as motors. no esc required, indie suspension and you coud do all kinds of skidsteer manouvers

[JohnRobHolmes]

Originally Posted by CheapTwin

I've thought about this for a long time and i was wondering if you could use 4 pcs. modified high torque brushless sevos as motors. no esc required, indie suspension and you coud do all kinds of skidsteer manouvers

It would probably work on a 1.9 size. Easy want to do it for sure.

[White Stripe]

I guess if you did that you could have one servo per wheel each on a seperate channel also and make it turn on a dime like that concept jeep chrysler built with the dual hemis in it. If its in a super though why not just use 4 540 or the little 380 or whatever they are brushed motors? Plus if they get wet its not as big of a deal. Man the tmaxx ball joints are so far apart you could almost pull the knuckle out and put a 540 motor in their. I don't know a lot about motors though so I could be way out in left field with this. Just shooting out ideas.

[fennex]

Quite some good answers! It is funny to see that this can be done in a 1:1 scale car but not in RC.
I had thought about having the motor parallel to the axle but maybe having the motors at 90 degrees (along the chassis), using a worm gear, with the spur attached to the wheel axle, would allow for torque and prevent freewheeling.
Yes, it would be a lot of work since the parts would be hard to find.

[Mad Dawg]

That is an interesting idea and could certainly be done.


The first thing that popped into my mind was clod stall....X4

[CheapTwin]

if run 4 motors with 4 esc's there is no chance for clod stall

[fennex]

Thanks for the answers. Quite interesting. I had originally thought of having the motor parallel to the axle (like an MOA setup) but finding a reducer seems not feasable.
So having the motors at 90 degrees and a worm gear may seem a better way since there is a great reduction and no freewheeling.
The Losi 1/10 has that sort of axle but instead of having 1 motor up in the centre, somehow combine 2 axles to make 1 with 2 worms and 2 1/2 axles, and the motors on the axle.
I know, lots of work, and probably more expensive than necessary.

But having individual control of each wheel could be interesting:
- use skid steering so no need for conventional steering (no servo)
- turn on a dime

[rooktakesqueen]

too much unsprung weight for crawling...Volvo has been working on this for their cars, find it online, cool stuff (for a car)

[rooktakesqueen]

Not true....unless you have each ESC hooked to it's own battery...even then, you're still going to have some stall

Originally Posted by CheapTwin

if run 4 motors with 4 esc's there is no chance for clod stall

[White Stripe]

What is the diffence though between a stick crawler with clods and a crawler with two motors per wheel? Both have a ton of unsprung weight it would seem. Not arguing just thinking. I guess someone would have to try it to see how well it would crawl for sure, but Im not gonna spend the money.$$$

[Terranaut]

Originally Posted by rooktakesqueen

too much unsprung weight for crawling...Volvo has been working on this for their cars, find it online, cool stuff (for a car)

On most MOA crawlers most of the weight is unsprung. The front axle alone includes the motor, transmission, servo, added wheel weights and of course the axle itself. That is probably half the weight of the whole rrig and it's all unsprung weight. Unsprung weight is not an issue for slow moving vehicles, certainly not a problem for crawlers.

Motor-in-wheel sounds like a great idea to me. Volvo must be near the end of a long list of companies already developing motor-in-wheel concepts for full scale cars. I think they'll be in the showrooms before we see it in R/C crawlers.

Cheers.