Steering for a 110cc 4-wheeler

@inq Ok, then I change my comment to (Usable Battery WH) / (avg steering motor watts) to yield hours of use before recharging.

(Usable Battery WH) is the product of AH and V all divided by 2. 

Also remember if it's a lead acid battery it will need at least overnight charging.

Under this usage scenario, the battery has to be a deep discharge and it will be a lot better with Lithium, specifically LiFePO4 chemistry. Check with local golf course for a supplier.

Good brands are Trojan and Crown. 12V is rare due to weight (130+ lbs), the 6V are 67 lbs each.

@zander @Ron

I have measured.  11.4in bar and 40lbs.  So I calculate 450.....

Of course I did let some air out of the tires to account for some of that and to give me some leeway.

Posted by: @mscientist33

@zander @Ron

I have measured.  11.4in bar and 40lbs.  So I calculate 450.....

Of course I did let some air out of the tires to account for some of that and to give me some leeway.

Wow!  That is a lot higher than I would have guessed.  I assume that is sitting still. 

That will be conservative.  IOW, if your motor/driver/gear combination can turn it in that situation, it should be good for all driving conditions except tire jammed in a ditch. 

The problem then since 450 is higher than 310 in-lbs, is you have to decide to either get a stronger motor or put the reduction gear in it.  

Case 1 - 1:2 reduction - you'll get 620 in-lbs and unloaded (on jacks) it should travel 61.5 degree in your chosen 500 ms.  Remember when loaded up, especially not moving forward, it will be under considerable load and will take far longer than that 500 ms to travel the 60 degrees.

Case 2 - If you want to calculate a gear ratio that "barely" can turn when not moving forward, it is just the ratio of torque 450 / 310 = 1.452 or 1:1.452  This will give you the torque to barely turn it in your test condition and give you an unloaded time for 60 degrees of 354 ms.  

Remember, these are all relying on data on the outside of the motor that are usually optimistic and when it was brand new.  I'd probably try to split the difference between the two cases and find a pair of gears giving a ratio around 1:1.72... 

i.e.... 13 teeth on the motor and 22 teeth on the steering head gives 1:1.69.  

Max torque 1.69 * 310 = 524 in-lbs

60 degree rate of 0.412 ms.

Good luck!

VBR,

Inq

@inq At least your comments show me that I was headed in the right direction.  I will try to 3d print for 15mm thick gears to test with (and figure out a way to actually mount the motor with the gears...)

Just as a side note... because the torque required was 450 in-lbs, your motor should NOT have been able to turn it directly connected.  I know that's stating the obvious (in hindsight) but that means there is still room to hope that the motor/driver/battery can turn it once you get the gear reduction in it.  SCORE!

I'll definitely chock it up as a data point.  My "feel" having never been on one was way wrong!

VBR,

Inq

@inq I hope he isn't moving forward or back when he turns thru 60 degrees in about 1/2 sec. AT any kind of speed that will result in an overturning. Remember, as the forward speed increases, the angle of the steering wheels needs to be much smaller. Go out somewhere with a lot of room and keeping the speed constant at say 20mph turn the wheel slow then turn it very fast. Let me know how it went.

@zander My turning angle is actually quite small on the small 4wheeler.  I'm expecting to actually stop the turning at about 30-40 degrees.  I also do not expect to be going really fast with this thing either, probably just a bit faster than walking speed (as of right now) and even still no faster than about 12mph.

Posted by: @mscientist33

@inq At least your comments show me that I was headed in the right direction.  I will try to 3d print for 15mm thick gears to test with (and figure out a way to actually mount the motor with the gears...)

I wish you luck, but I doubt any plastic gears will handle that.  450 in-lbs will be putting (a crude estimate) 10 ksi stresses on the tooth root.  That would require at least Aluminum or something stronger.

I still think it would be a great experiment though.  I'd test it up on jacks first without tires in contact.  If it even makes it through the first gear tooth, you might get an time estimate for your 60 degree arc.  Then try it on the floor.  I'm sure that'll set the teeth free! 🤗  Wear goggles!

Oh! And please take video of your tests.  I'd would really love to see the mayhem!  Seriously, I would like to see the failure mechanisms.  If your phone does slow motion modes, use that.

To try giving it a fighting chance, do you have Nylon filament?  It is what I use for gears and I've never busted one.  But, I have never used motors putting out 310 in-lbs.  Also they make a carbon fiber / nylon filament and carbon fiber / polycarbonate for 3D printing that THEY claim will approach aluminum properties.  I have a roll of this, but have not used it yet. 

"https://www.amazon.com/PRILINE-Polycarbonate-Filament-Dimensional-Accuracy/dp/B074DS3986"

https://www.amazon.com/PRILINE-Polycarbonate-Filament-Dimensional-Accuracy/dp/B074DS3986

@mscientist33 That sounds better.

@inq Believe it or not, I did actually have it working while the wheels where off the floor using PLA+ but I have been making the gears 15mm thick to have more surface area on the teeth.  I may actually try printing sprockets and using those (same 2:1 ratio) as I also have an RS40 chain available.  I will definitely do some videos when I get to that point.  For me, the biggest issue is how to get the motor and stuff mounted.... Even at a makeshift mount just to prove it out I can always machine it out afterwards (if it doesn't cost me an arm and a leg).

It lives!!  The PLA+ sprockets seem to be holding for now.  I will definitely order some metal ones now that I know it works.  I am using a servo tester in the video so I am in the process of putting it all together for the full RC experience.  I will have to add that it was my first welding experience.

With back wheels and steering.  I couldn't completely test it actually moving on the ground because my transmitter was dead and I have it wired to a power supply...  I will get a video of it on the ground outside when I get a chance. I've got it coded so it completely stops the motors if signal is lost to the transmitter.