Luckily, the Kelly controllers, while requiring some fancier wiring (pre-charge resistors, their own power source) than other motor controllers, were extremely easy to program. It is all taken care of in the series of menus seen below. To connect to the computer, you use the provided adapter (rear of the controller, above) to the serial port of a computer. The controller needs to be powered on to connect, but through its own power connection, not the power connections for the motor. The controller is powered through the power and ground prongs of the rear plug. Above, we used a pair of 9V batteries in series to power them. They need a minimum of 12V DC to operate.
Here we set whether to cut out if the voltage went above or below a certain level–important if you have a system that provides more voltage than a particular component can handle. You can also choose from a light, medium, or heavy load. We figured that propelling a human around a race-track should count as heavy.
After setting up the controller, you cycle its power to ensure the new options are loaded, and you’re good to go.
Warning: We only did this with professional assistance. If there is one thing you copy about what we did, copy our getting professional help with the batteries.
In the beginning:
There were some elements in the ground. A very, very long time later, after being turned into a Toyota Prius, some of those elements ended up on a table in a classroom. Thus, we received the full, Nickel Metal-Hydride, propulsion battery from a (2nd?) generation model.
The cells are held together by long rods with threaded ends. Once we removed the nuts holding it all together we could marvel at the lightness of the individual cells-only a couple of pounds each.
Those plastic end caps and long rods are there for a reason: the battery cells will expand if not kept under compression. Thus, before you disassemble the big battery, start planning how to compress the smaller kart batteries you will make. We used threaded rod and nuts to hold slabs of acrylic against the side.
Given more time to research how bicycle disc brakes mount, I would have taken us in a different direction. When using a split rear axle ideally you need one brake to mount left and the other to mount right; bicycle brakes do not allow for this mounting orientation. What we ended up fabricating was several unique components that will be pictured below that allowed us to use the stock bicycle mounts but orient them correctly to the vehicle. We also, thanks to input from another professor, mounted the brake calipers on a flexible system to allow the brakes to float so that they wouldn’t bind if anything on the vehicle shifted. This mounting has the potential to slightly reduce braking ability, but at the speeds power racing series vehicles operate it was determined not to be a major issue.
First a custom mount had to be fabricated to allow the disc to attach to the axle. This mount had to be removable but also strong enough to hold when the vehicle was braking. I designed a weld able steel mount that fit the bolt hole pattern for the disc brake, then welded it to one half of a two piece shaft collar. This meant the screws could be tightened very tight which gave us a good friction lock to the axle.
Mounting the caliper was eventually accomplished using 90° angle iron and screws. The screws were placed in clearance holes to the calipers and springs were put behind them to create the proper tension. This allows the floating discussed earlier. As you can see, the angle iron was welded to the bars which the motor mounts and axle pillow blocks attach to.
Having each brake independent allows us to break each wheel separately which tightens the vehicle turning radius and doesn’t require one to entirely get off the gas when braking around a corner.
I am lucky enough to have access to an abrasive waterjet at my work, which makes the fabrication of two dimensional parts significantly easier and faster. An abrasive waterjet works by forcing a large volume of water through a very small orifice creating a fine stream of very high pressure water (50,000+ P.S.I). This water stream is mixed with an abrasive powder of a specified grit (size of grain) to aid in the rapid cutting of material. A water jet can cut a variety of different materials ranging from insulation foam blocks to steel. It allowed us to rapidly fabricate the motor mounts as well as stronger driving sprockets, brake disc shaft mounts, and motor mount spacers.
The motor mounts were made from 0.5” 6061-T6 aluminum. Aluminum is a good material to use for this application because it has a high strength to weight ratio and is easy to machine. The design for the motor mounts was chosen to allow the pillow blocks to be mounted directly underneath without interfering. I would have liked to use thinner material to save on weight but 0.5” was used because slots were needed for the motor mounts to be adjustable with the axles. The front mount allows the motor to pass through and is then secured with a set screw to keep it from wiggling when in place. In the future I would modify the mount drawing to leave a bit more tolerance for the motors as they are not perfectly round or exactly the same diameter all the way through. I would also recommend prototyping the fit with a cheaper material as I wasted several large pieces of 6061 in getting the fit to each motor correct.
The drive sprockets needed a little bit more post processing after being cut on the waterjet because they needed ramped angles to ensure the chain stayed on them and didn’t slip if it got a little loose. Daniel Raver accomplished this task carefully using a belt sander. They were first prototyped to ensure a good fit and then waterjetted and processed.
Given enough time and raw material many more components could be made with the waterjet. Balancing time and cost is important though and it is often more viable to just by a prefabricated part then to make it yourself, but what is the fun in that?
Mounting the MTB bicycle braking system. Front and Back braking kit by Gasbike.
Based on the steering configuration that we gone with, we decided to use a Front and Back braking kit by Gasbike. The steering bar which came from a recycled bicycle allowed the 2 braking handles to easily be fitted on. We connected the braking cables to the braking handles. With the braking kit that we ordered, one of the cables was shorter than the other. We decided to assemble the shorter cable to the left hand brake handle. The longer cable was long enough to be able to run down the steering mount and along the right side bar of the frame to where it was able to connect to the right brake already mounted on the back. The left hand cable or shorter cable was ran down the steering mount and down the middle above where the battery was to be placed, with enough slack to place and remove the battery, and connect with the left brake already mounted on the back.
When running the cable through the brake, we need to ensure that the cable is as tight as it possibly can be. To do this, it required 2 people one to hold down the handle for the steering brake handle and compress the braking arm on the brake mount, while the second person took pillars and pulled the cable as much as possible to ensure a tight fit. This configuration allowed us to make a dual braking system.
For this project, most of the frame additions such as the battery carrier, seat mount, and petal mount, we just simple scrap wood that was available.
For the battery mount, we simply cut several ribs made of wood that would act as sort of an under carriage. The ribs were cut at the right measurements to where it would fit tightly against the frame. The ribs were secured to each other by 2 pieces of ¼ inch wood board, that we drilled screws into. The sides of the wood boards facing the battery pack would have to 2 notches cut out of them for the screw ends from the battery pack would fit into.
For the Petal mount, we cut a piece of wood board that matched the width of the go-kart frame. This would allow us to drill holes into the wood board and allow us to secure the board to the frame with something simple such as zip-ties. With the board that we used we had to cut a square out to allow room for the steering column to move freely. To mount the 5-volt foot throttle by Cisno we had to cut out a hole in the board to allow the pedal to comprise down. We mounted the pedal by cutting 3 holes that matched the mounting brackets of the pedal and running 3 screws underneath to secure the pedal from the bottom.
The seating mount was assembled using several pieces of wood boards. Based on certain time constraints we were unable to use metal as the mount. The seat that we used was a simple chair seat from recycled material. At the bottom of this seat, there was a mounting plate that allowed us to bolt the chair to pieces of 2×4 which was the length of the go-kart frame. To have a proper height off the frame for the driver. We simply secured more wood boards together. For us to mount the seating mount onto the frame, we drilled 2 holes on each side of the frame where the seat was to be mounted using a 3/8 drill. We ensured that the all set of holes from the wooden mount and the frame matched up and tightly bolted down the seating mount to the metal go-kart frame. To secure all the boards and seat together we used wood glue as well as 4 6 inch 3/8 bolts.
– 3d-printed mount for resistor, DPDT switch, fuse
-DC-DC voltage converter (in 18-75vDC, out 12vDC): CUI Inc. PYB10-Q48-D12-U
-throttle pedal input: 5V output 0.8-4.2V
-37.7v 5-cell NiMH batteries from Toyota Prius (2)
8AWG wire, approximately 15 feet (~5m) before cutting: 2 colors to differentiate positive and negative/ground, 13 total wires
20AWG wire, approximately 18 feet (<6m): 5 colors–positive and negative, different signal lines such as throttle, 14 total wires
-electrical connectors: inordinate, just keep buying them until they’re out of stock (26 of 8AWG and less than 28 of 20AWG–some of the small gauge wires are for plugs in the Kelly controllers, which come with connectors to wire up the paired plug
-2 Power Systems: one to power motors, and one to power motor controllers (here taken care of by voltage dropping on 2nd set of wires (37-12 voltage converter)
-Pre-charge resistor: small amount of current allowed through resistor to charge capacitors before fully opening main power contactor
To start our build, we chose a 36 volt system. Thirty-six volt systems have been used extensively in the Power Racing Series, providing guidance in our system build. Equally important, with 48 volt motors, any over-voltage problems in our nominally 36 volt system would not damage the equipment.
A Prius propulsion battery was donated to the team early in the build. With professional assistance, we parted out the battery into separate cells so that we could build individual ~36v batteries.
Currently, we are uncertain about the total amp-hours available from our batteries, and so plan to run two batteries in parallel to reduce drain on the system until we have more detailed data.
Though our initial decision to use Kelly motor controllers was cost-driven, they have proven to have several unanticipated strengths: For one, they can interact directly with a throttle rather than requiring a separate controller (such as an Arduino) to interpret between them. Second, though they require a serial port to communicate with for programming purposes, the interface is extremely simple and straight-forward, essentially amounting to answering a couple of questions.
On the other hand, the capacitors in the controllers require a pre-charge resistor to charge them before the system is actually “turned on” by the main power switch to prevent the initial current in-rush from either destroying the capacitor or shorting across the power connectors.
Thus, there are actually two parallel circuits at the point of the main power contactor, the switch itself, and by its side, the smaller DPDT switch and resistor.