Customer Handoff & Final Project Documentation
Table of Contents
Team Vision for Final Demo and HandoffDuring this phase we sought to
- Finalize assembly of combined subsystem.
- Prepare for and Exhibit at ImagineRIT
- Complete Technical Paper
- Finalize drawing package and documentation
- Summarize areas for possible improvements
During this phase we managed to
- Everything listed above was finished or completed.
Test Results SummaryMost of the tests could be completed as listed in the testing plans (Also here and here). However there were difficulties in performing the battery life test, as there were mechanical failings on the motor gearbox wheel assembly.
While trying to test the capability on more severe inclines, it was found that the omniwheel would not remain in place axially along the gearbox output shaft before ImagineRIT.
Because of this, a hole needed to be drilled perpendicular to the keyway. However the hole was not aligned with the midpoint of the keyway. As a result the set screw inserted would regularly fail as well. After bringing the gearbox to the machine shop again, another hole was drilled perpendicular to the key midway between the keyway so that the wheel hub would lie directly over the keyway.
Ramp Testing by team member Nick
Individual Test Results
Risk and Problem Tracking
Final Project Documentation
The motor has various operating modes. The two modes tested are speed control and torque control. Both of these modes are proportional to the duty cycle of a PWM signal. The higher the duty cycle yields the higher torque or speed. Each mode has its own advantages. However, the torque suits our need the best. In torque mode, when the motor is powered but duty cycle is zero, the motor is still free to spin. On the other hand, the speed mode prevents it from spinning to do 0% duty cycle meaning zero speed. The torque mode only has a max speed limitation, which is for shutting down the motor when the motor is at max speed for over 10 seconds. However, if the motor stalls, it will shutdown still. Please refer to the following document for more information about controlling the motor in other way.
In the case of stall, a buzzer would go off. The buzzer is controlled by the output signals HLFB+ and HLFB- coming from the motor. HLFB+ and HLFB- conduct when the motor is working. When the motor enters shutdown mode, these two signals become an open in the circuit.
From the control panel, there are two switches and one knob. One switch is a rocker switch that turns the motor on or off. The other switch is an emergency push button switch. It is a quick way to shut of the motor, it can't be turn back on accidentally. The knob is for changing the duty cycle of the PWM signal.
About the wiring connections, please refer back to Assembly Manual for how the wire connectors looked like. However, basically, the positive terminal, labeled as "Red", from the battery goes into the emergency button, to the rocker switch and the pwm controller. From the PWM controller and the rocker switch, the positive terminal comes back as the "Red Black" wire. This wire will then go into the power of the motor. The negative terminal is labeled as "Black". It goes into the PWM controller and to the motor directly. The yellow wires represent the PWM controller signals. The "yellow" is the positive, and the"yellow black" is the negative. The white wires from the control panel are the switch that splits the two sections in the schematic link shown above. The green wires in the box are connected to the enable of the motor. The PWM signal goes into the motor as yellow wires as well. The white wires coming out of the motor are the HLFB+ and HLFB-.
Recommendations for Future work
- Look into a lighter material for the mounting frame
- This rendition was 'disaster proof' and factor of safety was very large (~80). This could be reduced with minimal loss of durability.
- Make electrical circuit more robust
- As is, it is placed on a breadboard and is mechanically susceptible to vibrations during usage. Also markings and wiring locations are currently not very clear. Making a simple PCB for the circuit should be the next step.
- Find alternative to mounting bracket (with the
u-bolts) and the top links.
- While the top links were a good find as being
robust as well as cheap, they offer several
disadvantages in practice.
- Addition extends far beyond what was intended. If this protrusion could be reduced, the user's interaction with others would be improved.
- Because of the mounting bracket's construction, there is limited range of motion perpendicular to the direction of wheelchair travel. This is part of the floor limitation on the length of the top link section.
- The free rotation at the pin joint exacerbates the torquing problem.
- Mounting system is not universal. We can't guarantee that the posterior tubing will be present on all wheelchairs.
- While the top links were a good find as being robust as well as cheap, they offer several disadvantages in practice.
- Torquing problem
- In line gearbox has a few sub-optimal points.
- Because the weight is completely
perpendicular to the wheel, this torques the
motor-gearbox-wheel assembly. This results in
uneven wear on the wheel and an awkward angle of
- This could possibly be solved by transferring some of the weight from the mounting bracket to the opposite side of the gearbox. This would be more viable if a lighter material was used for said bracket.
- Because the weight is completely perpendicular to the wheel, this torques the motor-gearbox-wheel assembly. This results in uneven wear on the wheel and an awkward angle of attack
- In line gearbox has a few sub-optimal points.
- Research if a different gearbox could be used.
- A 7:1 gearbox was awkward to make, and a 10:1 gearbox could potentially be cheaper as well as easier to replace. If it was cheaper, an inline gearbox might be more possible. Also since the speed is overestimated, speed reduction from 10:1 gearbox shouldn't be a problem, while the extra torque gain can be useful.
- Weather Testing
- Testing the system in non-ideal weather, such as raining and snowing, isn't done. The control panel is exposed to weather elements. Wire connections are protected by shrink wraps.
Functional Demo MaterialsFinal Presentation Single Slide
Max Incline Test: https://www.youtube.com/watch?v=vhn57Zr9fn8
Max Distance Test: https://www.youtube.com/watch?v=dNdWmki-pTA
- Notes from review
Plans for Wrap-up
The last thing needed to be done was documentation. The project works as intended, though there are many aspects that can be improved with extra time and money. Most problems encountered were solved by changing the motor operating mode from speed control to torque control. Torque control has the flexibility of letting the motor to operate at any speed under the programmed max speed as long as the torque stays at assigned value that is controlled by the PWM controller. When power is on, the motor is no longer locked into place because the motor is providing no torque, allowing the user to push him/herself.
With assistance, the system can propel the user up an incline as seen in the max incline test. On its own the system does have some difficulty in propelling itself. This can be solved by changing increasing the gear ratio of the gearbox. However, it can also be done by adding another 12V battery in series to increase the power. There are trade-offs between either large amount of additional funding or increased weight. The weight issue needs to be resolved and can be adjusted by changing some of the materials used.
The wheelchair and system will be returned to the BAD lab (as that was the 'official workspace'). There is a possibility that Alan will take it to the end user for opinions/critiques. If this is the case, he will be in contact with the MSD department.