PolyBOTS

Botmobile

Botmobile
Authored by Yuri

The Botmobile is an evolutionary step to the previous projects of that sort.   The Botmobile is a chair with electric motors attached.   There is nothing more exiting in robotics, that to ride on the robot itself.   The difference between wheel chair and Botmobile is that Botmobile is faster.

The Botmobile is simply a regular office chair partially taken apart and attached to a frame that hosts batteries, controls, motors, wheels and all the parts.   The robot reuses a lot of previous project parts.
The drive units consist of motors, transmissions chains and sprockets.   The robot has 2 wheel drive; meaning that 2 out of 4 wheels powered.   The final drive ratio is 20 tooth and 12 tooth transmission.   Meaning that for 20 revolutions of the transmission, the wheels will turn 12 revolutions.   The transmission hosts two motors, CIM FR801-001 and FR801-005.   The rear wheels are 10 in diameter and 3 in width.   The transmission has 2 speeds, Low and High.   The low gear is 10.67:1 and high of 4.17:1.   Since 4 motors in total are driving the robot.   The combined Horsepower is 1.0584HP.

The robot has active steering, not like old models where the front wheels where casters.   But in Botmobile power steering is present.   The steering is actuated via a window motor from a vehicle.   The motor drives the main gear through a warm gear.   That allows the steering to lock in a specific position.   And under load it would not rotate back unless specified by the driver.   The front wheels are 8 in diameter 1.5in wide.   The wheels are in double shear to provide sufficient support.   The fork that supports the wheels is connected to the frame through the front bulkhead that also hosts the motor.

The majority of the frame is made from 1×1 in aluminum U channel.   The primary cross member is made from 5×2 in aluminum C channel.   The front bulkhead is made from 2×4 in aluminum rectangular tube.   The batteries are located in the middle between primary cross member and front bulkhead.   There is sufficient space left to place 3rd battery under the seat, a generator or it can be converted into luggage compartment.
The electrical system is split into 2 parts.   One supplies primary power to the motors and the other is the control system.   The primary power is made up of 2 truck batteries in series total to 24V and total of ~1000cca, or ~1250CA.   That in term ends up to about 63Amp-Hr.   That ends up to ~1.5Kw-hr of power available.   In terms meaning that a robot driving at constant speed would drive for 1.25hrs nonstop.   At top speed it would cover almost 29 miles.   With 36V primary power system, the range would extend to 44 miles or 1.92 hrs of driving.   The motors are wired in series so that the voltage would double to 24V but amperage required would be averaged.

The control circuit is made of motors controllers, programmable controller and user input controls.   The only motor controllers Polybots have at a time that can be use in this project are victor 883.   For a 36V to 60V system, victor HV36 or HV48 would have to be used.   The logistic controller is used to calibrate and recalculate user controls output into motor controllers input.   The controller would also calculate the velocity of the robot and would output that to a speedometer made out of 5V analog voltmeter.   It would also locate the steering position so that the steering would be linear.   Because the velocity is calculated, it would be possible to set speed limits, so that the robot would not get damaged.   The user controls the robot through Nintendo steering wheel and pedals.   They were present in Polybots and would work best with the Botmobile.   The easiest controls for the robot are steering wheel and 2 pedals.

Future upgrades
One of the main upgrades would be to make a full or partial body for the robot.   Since most parts are showing.   To make the robot more pleasing all the parts should be covered up.   The least expensive way would to make an aluminum body.   The most expensive way would to make fiber glass of carbon fiber body.
Since the robot uses permanent magnet DC motors.   It would be possible to convert part of kinetic energy into DC current.   Using couple of relays and resistors it would be possible to make a circuit that would gradually apply breaks by recharging the battery.   It would be also possible to use a motor controller in reverse, where power is supplied from the motors to the batteries.   In any case, a rectifier bridge would be used.     In case strong breaking is required, a reverse voltage can be applied to stop the robot.   For the regenerative breaking, it would be easier if there be only one Victor controlling the drive motors.     Victor 885 would work the best.

It would be possible to add 3rd battery under the seat to greatly extend the range of the robot.   Another truck battery can fit transversely under the seat.   That would allow the system to be 36V and overload of the motors can be done up to 50%.   It can also be limited so it would not overload the motors.   Since the motors are using motor controllers, it is easy to control the voltage going to the motors.   Adding a thermal coupler would allow having controlled overload where exact condition of the motors can be monitored.
Another possibility is to use the space for a small generator.   When needed it would start up by itself and refill the batteries with power.   Smallest 2 stroke motor would be a weed whacker motor.   They would be perfect for the job.   Since most of them are above 1HP, the robot can drive and recharge from the generator.   The alternator can be from any vehicle.   The lowest alternators on the cars are of 30amps, most are in 60 amp area up to 200 amps.   The alternator can be modified to run as a motor to start the engine.   While the alternator and engine would be mated through a flexible coupling.

Another upgrade would be to have ability to monitor batteries automatically, meaning that the controller would be able to monitor the condition of the batteries.   Simple circuit of resistors would suffice.
The performance upgrade would be to all capacitors of about 5 Farads to every battery in parallel.   This would allow having sufficient power for the motors to start moving.   The large loss of initial start up would diminish.   The Lead acid batteries prefer not to supply high current for a small burst.

Specifications:
Motors:
Name       Volts nominal     Peak Pwr     Stall torque     Stall amps     No load rpm     No load amps     HP @65%eff
FR801-001       12                   337Watt                 343.4 oz-in           133                                         5310                         2.7                   0.2937
FR801-005       12                       270Watt                       570 oz-in           96                                             2700                                  1                    0.2355

Batteries:
Two truck batteries from E350 vans, one 1000cca and another of 850cca, average of 45lb charged up.
Performance:
Low gear 10.67:1
High gear 4.17:1
Final gear 1.67:1
Total Low gear reduction: 17.82:1
Total High gear reduction: 6.96:1
Wheel RPM in low gear max: 282 RPM
Wheel RPM in high gear max: 763 RPM
Equivalent top speed in Low gear: 8.4 MPH
Equivalent top speed in High gear: 22.7MPH
Combined HP:   1.0584
Motor Controller:
Control Signal Standard R/C Type PWM (Pulse Width Modulation)
Operating Voltage 6V to 30V (does not include the fan)
Fan Type Rotron.   Battle proven by Inertia Labs (and many others).
12V Fan Voltage 6V to 16V
24V Fan Voltage 16V to 30V
Maximum Current 60A continuous
Surge Current 100A for < 2 second 200A for < 1 second
Power Connector 6-32 Screw Terminals
Signal Connector Use a standard non-shrouded PWM cable (3 wires)
Typical Application Power one motor with variable speed forward, reverse, or off
Weight 0.25 lbs

Links:
Transmission
Motor Controller