Need Help with a Rear Wheel Drive Car Style Robot

[Schlayer]

I am a high school student who has long been interested in and involved with robotics and similar projects, and I've been working on building a robot with a car-style two wheel steering, but I've hit a bit of a roadblock. To keep complexity low I'm trying to get away with using either very simple or no suspension, and I cannot think of a great way to mount my motor/rear Axel shaft such that it can survive vibrations without causing damage to my gears or motor.
I am planning on running a 4.5:1 or 5:1 gear ratio, pinion and spur directly meshed together with the spur on my rear Axel (a 3/8" thick solid steel shaft) and my motor is a pretty powerful 545 can from Banebots. It will be driving my robot really fast and with considerable torque, theoretically my robot should be able to get over 30mph easily. I have access to hose clamps, HDPE sheets that are 3/8" thick, some 1/4" Lexand, 1/8" plexiglass, and a lot of aluminum L brackets, flat bars, and square tubes. Any suggestions would be greatly appreciated!
I have only hand operated power tools to work with BTW, but I can easily cut plastic and aluminum with my dremel and I have a nice high torque drill, plus soldering equipment and a blowtorch. I have access to plenty of fasteners and misc. materials as well, and can purchase anything cheap and readily available online/in hobby or hardware stores.
So far my goal is roughly to create a 1:10 scale RC car and then add some autonomy through an Arduino Mega. I have all my electronics already purchased and have done my homework to figure out speed, acceleration, and approximate weight for my robot. Ultimately it'll be about 18-22" long and about 12" wide, under 3.5kg/7lbs. I have some Banebots 3-7/8" wheels for the back. I have some skateboard wheels from an old project I plan to use for the front wheels since they have bearings mounted already, but I have another pair of the same Banebots wheels in case that might work better once I test it out in real-life conditions.

TL;DR: I need a super simple way to make a motor and gear system survive vibrating while spinning at high speeds, and other tips/suggestions.

[Gertlex]

The wheel/tire can always add a level of shock absorbing.

I'd be more concerned about what happens when you flip the car at 30 mph (or 10 mph even).

(I'd suggest splitting up that giant paragraph into a few coherent pieces. I might have had ideas while reading it, but lost track of them in keeping track of where I was in that paragraph...)

[Schlayer]

The wheel/tire can always add a level of shock absorbing.

I have already tried to address this in part with my chosen wheels; they come with a sort of foam-rubber material moulded on as a tire and have different hardness-es. I got Shore 40A and 50A hardness wheels (1 pair each) and my skateboard wheels should have a hardness of roughly Shore 75A, which is not soft enough to 'give' much under such lightweight stresses. I have some ideas for adding suspension to just the front wheels already, should I stick to the skateboard wheels.

I'd be more concerned about what happens when you flip the car at 30 mph (or 10 mph even).

Yeah... I was thinking of buying some 1/8" aluminum dowels and bending/cutting them into a sort of roll cage, but there could be a more elegant solution. I will probably use foam tape to add a nice cushioned bumper in the front and rear for lower speed collisions. If you have a better idea for a body protection method, let me know!

(I'd suggest splitting up that giant paragraph into a few coherent pieces. I might have had ideas while reading it, but lost track of them in keeping track of where I was in that paragraph...)

This has been addressed, thanks for the warning.

[Schlayer]

Other than worrying about vibrations within the chassis of my car, I realize winter is coming (get the reference?) in my area. I know that waterproofing isn't usually a concern for freshwater such as rainwater or melting snow (though pollutants might contribute to raised conductivity as I live near Philadelphia), but I fear for my receiver and ESC. Would simply building enclosures from Plexiglass suffice to protect my components from a little rainwater? Also, if I go through with my plan to add an Arduino to this bot, would it be worthwhile to buy a pre-manufactured enclosure?

[bdeuell]

First for vibration ... without getting into the details of vibration dynamics and ignoring things such as natural frequencies:

I would be primarily concerned about the vibrations from an unbalanced or poorly designed drivetrain; as your drive shafts, gears, and wheels will be spinning quite fast any misalignment or unbalanced mass will result in high frequency vibrations (as well as many other issues). I recommend taking extra care in the design, manufacture, and assembly of these components to make them as precise as possible.

While vibration from the ground will certainly be present the effects will be lessened by the fact that most of your components will have a relatively low mass. I think you can address this vibration effectively without building a complex suspension system. Firstly using the wheels to adsorb some vibration is a great start. Secondly make sure all components are rigidly mounted (especially the heavier ones). Third use vibration isolating mounts on sensitive components (such as the electronics).


Now the rain protection issue (ingress protection):

I would not plan on any water being nonconductive; I doubt you would count on your computer being able to work in the rain. If you plan on using your robot outside and definitely if you plan on using it in the rain I would recommend some level of protection for your electronics (in particular the circuit boards that have closely spaced IC pins ... less distance for the electrons to travel).

The plastic enclosure on your receiver or even a piece of plexiglass over the electronics will offer some level of protection but if you truly want to operate in the rain i would go a step further. The integrity of any enclosure you build depends on your design and how well it is constructed (so its hard to give you an assessment on its effectiveness). Buying an enclosure might be a simpler option but be aware any modifications you make may impact the integrity of the enclosure. A little reading on Ingress Protection or NEMA ratings might give you some ideas on what level of protection is appropriate for your application.

[Schlayer]

Thank you! This all seems quite helpful, especially the vibration dampening idea. I hadn't really considerred isolating the components to handle vibrations away from the main chassis, and that sounds promising. I will likely use Velcro for the battery which should cushion it considerably, and I got some two-sided foam tape that I can probably secure everything else in tandem with zip ties except the motor and servo.
The way I configured my steering mechanism is going to make waterproofing the servo difficult, but I might just wrap it in a balloon or other thin walled plastic layer. I know DC motors themselves are pretty electrically sound when wet, but if I find a way to manufacture a curved plastic shield I might look into that.

Now the rain protection issue (ingress protection):
The plastic enclosure on your receiver or even a piece of plexiglass over the electronics will offer some level of protection but if you truly want to operate in the rain i would go a step further. The integrity of any enclosure you build depends on your design and how well it is constructed (so its hard to give you an assessment on its effectiveness). Buying an enclosure might be a simpler option but be aware any modifications you make may impact the integrity of the enclosure. A little reading on Ingress Protection or NEMA ratings might give you some ideas on what level of protection is appropriate for your application.

I looked up some arduino enclosures and they are pretty cheap so I will probably get one of those.  As for the other parts, I doubt I will be able to find part-specific enclosures, so plexi will probably be fine. I couldn't find NEMA ratings on small electrical enclosures, it seems those mostly matter for industrial applications, but I have seen more general claims such as 'weatherproof' and 'waterproof' and the like on several models.
I bought some single pin breadboard jumpers for the testing phase when I finally buy the Arduino model I think will work best, but I bet I should solder connections that aren't directly to the arduino headers before I take it for a spin. I'll probably use heat shrink to insulate any soldered connections as another water precaution, and if I figure out a really rock-solid configuration for the arduino headers I might be able to seal off the slits the enclosure comes with on top using hot glue so it is totally watertight. I definitely wouldn't need to make any more cuts in the enclosure, so it shouldn't compromise anything except my ability to move around the jumpers.

[CJAlbertson]

FIRST:  Slow the robot down to some reasonable speed.  30MHP is way to fast and there is no way on earth an Aruino based controller can provide any amount of autonomous control to a 30MPH model car.   What kind of sensors can you install that can see far enough ahead and how will you process data from those sensors to control the robot's behavior? 

As a rule of thumb, make sure that you are able to run faster than the robot can move. 

If this is an RC model race car then faster is better and the control problem is solved because YOU are driving it.  But if you are bulding a ROBOT and not an R/C car then the FIRST step is NOT how to mount a motor or vibrations but CONTROL ALGORITHMS.  Then you design the motor and steering to support the control algorithms.   For example odometry is not needed in an R/C car but a robot will want encoders on the motors or wheels to control eh motor speed under different loads with a PID control loop.  How will you arduino even know how fast the robot is moving or if it is turning to even if the wheels are on the ground.    All this matters MORE then the questions you asked.

So back up and make a decision.  Is this an RC car or a robot?  If a car then have fun but if it is a robot think FIRST about how sensor data will be used and what kind of sensors you need and then what kind of platform can cary those sensors.  A third options "both"  make two projects the RC car and a robot.  The robot needs to move about 2mph at most or then you have to consider momentum in the controller and the math gets really hard and you need a much bigger computer.

[Schlayer]

FIRST:  Slow the robot down to some reasonable speed.  30MHP is way to fast and there is no way on earth an Aruino based controller can provide any amount of autonomous control to a 30MPH model car.

     The entire point of a speed controller is... well... controlling the car's speed. I can't really avoid sounding condescending here, but please believe I don't mean to offend. I see that you don't understand what I meant by "robot" and "some autonomy" exactly so allow me to explain. I hadn't intended to drive my car bot at 30MPH while attempting to fully control its actions via Arduino, and in fact I anticipated those exact concerns with sensor data if I were to attempt it.

If this is an RC model race car then faster is better and the control problem is solved because YOU are driving it.  But if you are bulding a ROBOT and not an R/C car then the FIRST step is NOT how to mount a motor or vibrations but CONTROL ALGORITHMS. 

     I intended two different capabilities: RC control, plain and simple, and the ability to switch over to an Arduino for pre-programmed dumb routine following. I didn't mean for it to be live interpreting sensor data to control 100% of its actions, and if I do try that I definitely wasn't planning to do so at 30MPH. There is no reason at all to limit the top speed of my car just because it needs to at one point go slow.
     As for the control algorithms, since I am not doing any live interpretation of data I feel that this is not particularly useful, but aside from that I have to build the robot before I know how it will behave in reality to sending servo control values and speed controller values. I appreciate the concern but my intentions don't exactly line up with your interpretation.

     In other news, I have found that the outer diameter of my motor is exactly 1-1/2 in, so I was able to find plumbing pipe clamps which fit that diameter comfortably to mount it securely to an HDPE plate with regular bolts. I am having to switch to a larger spur gear to allow for clearance between said mounting solution and my rear axle shaft, so my speeds will be reduced somewhat due to the gearing ratio being raised from 4.0 to 4.5.