Introduction: Minimal Four X 12 Volt Rover Chassis With GoBILDA
I'm going to show you how I built an RC or autonomous rover chassis using goBILDA components. I should add here that I have no connection whatever with goBILDA other than as a mostly satisfied customer.
I've included a complete parts list under Supplies below, but for each step I'll list exactly what you need.
At the end I'll show you some ways to add structure to the backbone, and I'll add some general comments about motor drive electronics.
You can get these parts at https://www.gobilda.com
- 1 x 1121 Series Low-Side U-Channel (17 Hole, 432mm Length)
- 4 × 1102 Series Flat Beam (29 Hole, 232mm Length) - 2 Pack
- 2 × 1120 Series U-Channel (1 Hole, 48mm Length)
- 4 × 1121 Series Low-Side U-Channel (1 Hole, 48mm Length)
- 4 × 5201 Series, 53:1 Ratio, 105 RPM Spur Gear Motor w/Encoder
- 4 × 1701 Series Face Tapped Motor Mount (16-3)
- 4 × 1310 Series Hyper Hub (6mm D-Bore)
- 2 × 3605 Series Hurricane Rim - 2 Pack
- 2 × 3609 Series Cougar Tire - 2 Pack
- 1 × 7mm Combination Wrench
- 1 × 3mm Hex L-Key
- 1 × 2.5mm Hex L-Key
- 1 × 2802 Series Zinc-Plated Steel Button Head Screw (M4 x 0.7mm, 8mm Length) - 25 Pack
- 2 × 2802 Series Zinc-Plated Steel Button Head Screw (M4 x 0.7mm, 14mm Length) - 25 Pack
- 2 × 2801 Series Zinc Plated Steel Washer (4mm ID x 8mm OD) - 25 Pack
- 2× 2812 Series Zinc-Plated Steel Nylon-Insert Locknut (M4 x 0.7mm, 7mm Hex) - 25 Pack
- 1 × 2800 Series Zinc-Plated Steel Socket Head Screw (M4 x 0.7mm, 12mm Length) - 25 Pack
- 1 × 2809 Series Zinc-Plated Steel Split-Lock Washer (4mm ID x 7mm OD) - 25 Pack
- 1 × 2811 Series Zinc-Plated Steel Hex Nut (M4 x 0.7mm, 7mm Hex) - 25 Pack
- 1 × Plastic Grommet (14-1) - 12 Pack
- 1 × Rubber Grommet (14-2) - 12 Pack
Step 1: Basic Toolkit
These are the only tools you really need.
- A square. A machinist's square is nice to have but, really, any square, even a plastic square, is better than no square.
- 2.5 and 3mm hex keys and 7mm wrench from goBILDA. These are included in the parts list. If you already have a set of metric hex keys then you don't need these. But even if you have a nice set of metric combination wrenches, get that thin one from goBILDA.
- 2.5 and 3mm hex drive T-handles. A T-handle can flywheel or "twirl" in a way that no screwdriver type ever will. It can also apply that extra bit of torque you need for some parts like the clamping hubs we're using for the wheels.
- 7mm nut driver. Get the kind the pros use, as shown. You need the same torque they do.
You could probably put the whole thing together with the three tools from goBILDA, but it wouldn't be much fun. Generally, we use a hex key to hold a machine screw while we tighten a nut with a nut driver, and we use a wrench to hold a nut while we tighten a screw with a T-handle.
Step 2: Build the Motor Cages
Let's get started. Bolt together two motor cages. Here's what you need for each one:
- One channel for the center.
- Two low-side channels for the ends.
- Four flat beams.
- 16 each of M4 x 14mm button head screws, flat washers, and nylok nuts.
The drawing shows a 43mm spacer in the open end of the channel, but this is optional.
Build the motor cages on a dead flat surface, as follows:
- Bolt each beam to the center channel with two 14mm button head screws, flat washers, and nylok nuts.
- Square everything up.
- Add a low side channel to each end with more 14mm button head screws, flat washers, and nylok nuts.
- Square everything up.
- Tighten everything down.
And that's the hardest part done. Now we just need to add a backbone to complete the frame.
Step 3: Add the Backbone
Now we're ready to tie the two motor cages together with the backbone. Here's what you need.
- One low side backbone channel.
- Eight each M4 x 12mm cap screws and split lock washers
- 16 plain hex nuts
Each motor cage is attached to the backbone with four cap screws. We're going to install the cap screws on the motor cages with plain hex nuts first. This is so you can remove the backbone later after the motors are in, without losing the screws. Here's how we do it:
- Pass the cap screws up through the center channel of the motor cage, and thread a hex nut on each one just finger tight.
- Line up the third big hole of the backbone channel with the big hole in the motor cage center channel and press it down over the cap screws.
- Square everything up.
- Now reach in with that thin wrench and hold each nut while you tighten the bolt with a 3mm T-handle.
- Square everything up.
- Add a split lock washer and hex nut on each screw above the backbone and tighten down with a 7mm nut driver.
- Install the hard plastic grommets as shown in the photos. They should protrude about a mm into the motor cage.
And that's it. The frame is complete. Now we're ready to add the motors.
Step 4: Add the Motor Mounts to the Motors
We're finally going to get the motors on. But first we we need to attach the motor mounts to the motors. The motor mounts are really nothing more than hole pattern adapters: they allow us to bolt a component with one pattern and/or size of holes, to a component with a totally different arrangement.
Bolt the motor mount to the motor with the six included M3 screws. It will only go on one way.
My mounts came with pretty sub-optimal Phillips drive screws. Even though the part drawing from goBUILDA has cap screws as shown in the drawing above.
I replaced the bad screws with M3 x 6mm socket head cap screws as shown in the photo.
Now we can attach the motor assemblies to the frame.
Step 5: Attach the Motors
The illustration show everything right side up, but you want to turn the frame upside down for this.
One note: if you're going to add encoder cables to the motors, now would be a good time to do it. OK let's get rolling. For each motor:
- Start the wires through the plastic grommet.
- Get the motor in place and finish hauling the wires through.
- Bolt the motor mount to the motor cage end channel with M4 x 8mm button head screws. It will only go on one way.
You can use from four to eight screws for the motor mount. Six seems about right. Eight seems excessive and unnecessary. I used eight.
And we're almost there. We just need to get hubs on the motor shafts and we can bolt the wheels on.
Step 6: Attach the Wheel Hub to the Motor Shaft
For each motor:
Place the hub on the motor shaft. Use a spacer to make sure all four hubs are the same distance out. I use a 6mm hex key, but anything about 6mm wide will do. With the spacer in place, tighten the two clamping screws alternately until they scream in harmony.
And you're almost done. Time to put the wheels together and call it a day.
Step 7: Assemble the Wheels
The tires come with foam inserts. I find the best way to get the inserts into the tires is to fold them in half and just jam them in. Massage them a bit until the whole tire feels equally stuffed.
Now we're going to mount the tires on the rims to complete the wheel assembly.
The tires are directional, and the rims are not symmetrical. Here's how to make sure not to screw this up:
- Arrange the four rims in a square as shown above, with all the shallower center wells facing inward toward the opposite rim.
- Arrange the tires beside the rims so the tire treads are all pointing the same way.
- Grab each rim and tire and force the tire on the rim without turning anything around.
- Push the tire around with your thumbs until both beads are totally seated in their slots in the rim.
- Glue if desired and leave overnight.
I didn't glue mine and the thing seemed to do alright tooling around the tennis court (tennis courts generally have good traction, so you don't get much wheel slip). The tires did come off however during some rather rigorous bench testing later on. Then I glued them.
People seem to feel strongly about their tire glue, possibly in proportion to what they've spent on it. I've had pretty good luck with MG Chemicals AC. As for how to glue them, there are plenty of videos out there on just that very topic.
Now we can bolt the wheels on.
Step 8: Bolt on the Wheels
Arrange the four wheels around the frame with all the shallower center wells facing inward and tire treads all pointing the same way.
Finally, bolt each wheel to its hub with four M4 x 12mm cap screws and split lock washers, as shown above.
And that completes the basic assembly.
All that's required now is some basic electronics and you're good to go.
Step 9: Options for the Body
Here are some additional ideas the body. You can cap the backbone with up to three 5 hole pattern plates, or up to three 5 hole low side channels, or one long low side channel, or one or more grid plates, or something else. The box shown is a Hammond aluminum case just 2mm shorter than the backbone.
Step 10: Adding Electronics
There are motor controllers and motor drivers. Motor controllers operate on a higher level in the scheme of things that motor drivers. Typically we talk to motor controllers with servo pulses from an RC radio receiver, or with serial communications from a processor of some kind. Motor controllers come in one or two channel.
Motor drivers on the other hand operate on a more basic level. We talk to motor drivers with a PWM signal from a processor.
If you're building a strictly RC vehicle then a two-channel motor controller might be for you. You just need to wire the two motors on each side in parallel, connect the throttle and steering channels from the RC receiver, add a battery, and you're good to go. For this vehicle you'll need a controller that can handle about 15 Amps a side.
When we add a processor to the mix, though, things get more interesting. Now we read the data from the receiver with the processor. Nowadays this can usually be done with a simple serial link. Then we can send the throttle and steering data to the motor controller over a second serial link.
Or, we can use simple motor drivers and control them directly with PWM. We don't need to wire the motors on each side together. Each motor can have its own driver channel. Motor drivers come in one, two, or four channel, that I'm aware of. For this vehicle, one two-channel driver at each end seems like the most sensible arrangement. I use four single-channel drivers.
The drivers I use are about ten bucks US each. They handle 13 Amps continuous without a heat sink. They do locked-antiphase or sign-magnitude PWM with two wires plus ground. The only negative is they don't have a current sense output. They are called Cytron MD13S.