I have enjoyed seeing remote controlled trucks come a long way over the past couple decades. I've even owned several of them along the way. It all started with the AA powered 2WD trucks with simple springs as shocks. Then along came 7.2V with oil filled shocks, then 4wd, then NITRO powered and then 2 speed transmissions capable of 50MPH with reverse. The past several years the industry has had no where to go except bigger. From 1/16th scale to 1/10th scale and even 1/8th scale. Well, I'm going to beat everyone to the punch. I'm going to design and build a 1/4 scale remote controlled truck with my own unique twist.
Step 1: Start With the Frame
Step 2: Suspension Linkage
This is after the upper parallel pin is installed using H-links and the pneumatic cylinders (soon to be converted into hydraulic adjustable shocks) mounted. The engine is just sitting on it's mounts for now. But the differential and pillow blocks are in place. I had to design, weld and machine a sprocket that would fit perfectly over the differential and use the existing bolts. Then I designed, welded and machined a sprocket incorporated with the drum brake and wheel hub that fit the moped engine. Of course I crunched some numbers and calculated for a proper gear ratio. The differential sprocket is a 40 tooth and the drive sprocket is 15 tooth. This should give an end result similar to the moped's original ratio and performance which was speeds up to 48mph. Whooahh Can't Wait!!! I better plan on having an EASILY accessable kill switch on the vehicle and the remote.
Step 3: Make Shocks
Step 4: Mount the Motor
Step 5: Add Tank and Body
Can you see the proper springs under there now? I designed and machined spring guides and stops out of aluminum specifically for this project. Boy were those a pain to install! Also notice the muffler's under the rear wheel well and the gas tank under the dash. You can also see the servos on the drivers side swing arm. I coupled 2 super high torque 1/4 scale airplane servos together. They don't seem to have much power and the pull-pull cable system seems to have a little too much play so we'll just have to see how it all work out. This engine is electric start too! Yeah baby! I used two 6 volt batteries so I can split my RC controlls off of one and use them both in series for starting and getting charged by the engine. Oh, yeah, the engine is a 50cc air cooled two stroke with and automatic variable belt transmission out of a honda moped. I just happend to have rebuilt it about a year ago and had it laying around. You can also see the servo horn (small white round) just above the muffler. It's mounted to the engine and controlls the throttle and brake.
Step 6: Heavy Duty Steering
I've been asked for plans on my steering "servo". Where do I start. First of all my truck is 12V but the radio stuff is 6V so I paralled two 6V batteries so they could be used to start the engine and get charged by it too. Then I just pulled off of one battery to power the receiver and servos. With that said. The solid state relay dirver I made for the actuator is controlled by 6VDC pulsed from the servo board but switches 12V source power to the actuator. You MUST use solid state relays and not the coil type because of the fast pulses. Also, you must use 4 of the. Two for left (+ and -) and two for Right (+ and -). All the relays do is take what the servo board sends to the servo motor and controlls the relays with that signal to give a similar signal only 12V and high amperage.
Here's the schematic. (REVISED 01/02/09 ... Thanks to Alan)
Step 7: Steering Servo Circuit Pic
R, C & L are just soldered to the terminals where I removed the pot off the servo board so I could rig a pot on my steering linkage and it would give the proper signal to the servo board. I drove it without the pot in place and just soldered on there and in center position for a while but it doesn't have the "centering" effect. You have to steer left and then steer right to straighten it out.
Yes, messy and crude but it get's the job done and very nice and smoothly too.
Step 8: Complete Servo Actuator
Step 9: Videos
Step 10: THE END
Well, it's been fun. Unfortunatley I don't have room for this beast in my garage so it's getting disassembled soon. All in all it worked out pretty good. I got the idea out of my head and all I wanted was to see a working prototype. So, these parts will sit on my shelf until I come up with something new to make. Any ideas?