McPappy Racing Brushless Chassis Dyno
Today's brushless racing introduced new variables (mechanical timing, speedo timing, RPM ranges, rotor diameters) on top of the rollout variable. The new McPappy Racing DIY Brushless Chassis Dyno helps you to make sense of some of that. This dyno platform will allow you to test your motors against a brushless slave motor that provides consistent resistance from test to test.
The RC chassis dyno can provide 5 styles of testing:
The flywheel provides inertia resistance and the brushless slave provides constant resistance. Together they reproduce similar track resistance. The key component to this dyno platform is a huge peice of 1/4" 6061 aluminum which acts as a giant heat sink. Two large fans and all of that aluminum mass will bring the temperture of the motors and resistors back down to room temperature very quickly. This allows you to run many tests very quickly. To find your most powerful motor and speedo combination is actually quite simple. Your overall goal is to spin the flywheel and slave motor as fast as you can with the least amount of amp draw. The McPappy Racing Brushless Chassis Dyno can help you do just that. You will be able to find your strongest motors and most efficient combination of mechanical timing, speedo timing, RPM ranges, and rotor diameters.
Chassis Dyno Testing
The first testing configuration is chassis dyno. Chassis dyno testing offers the most convenience, as you simply set your car down on it and pull the trigger. This convenience allows you to try many variations and find the power you want quicker. You can also share numbers with other racers (regardless if the speedo and motor are different) to get the power dialed in very quickly. The chassis dyno can accommodate most 1/10th, 1/12th, and 1/18th, RC pan cars, dirt oval cars, touring cars (with front wheels propped up), buggies, etc. The acrylic platform measures 18.1" x 10".
It can fold up for portability or to save workspace.
A look underneath the acrylic platform:
Direct 'Motor Only' Testing
Direct ‘motor only’ testing is a bit more work to set up, but it provides an additional level of precision because it removes some more variables. If you are looking to find small differences, direct 'motor only’ testing can be worth the effort. Whichever test method you are using, your overall goal is to turn the slave motor as fast as you can with the least amount of amps.
The 2nd test configuration is a straight coupler between your test motor and the slave motor. Notice that we provide flex tubing. Compared to a solid metal coupler, in our testing, we found the flex tubing removes vibrations and produced better consistency. Click the pictures for higher resolution.
The 3rd test configuration is a direct coupler with a flywheel between both motors. This is an excellent combination of resistance to reproduce a similar track feel. The flywheel will test the bottom end of the motor under accelaration, and the brushless slave will provide resistance similar to drag produced by aerodynamics and tires at speed.
The 4th test configuration allows for the motors to be offset allowing you to use pinions. This opens up new possiblities for testing different gear ratios and assisting you with finding better rollouts. You'll be able to answer questions like, "Is higher timing + lower rollout better than lower timing + higher rollout?"
(The flywheel can be positioned on the test motor or slave motor.)
Motor Mount Adjustability
The dyno base allows the motors to slide to the desired location depending on your test configuration. The slots are machined to hold the locknut so that you can tighten or loosen the screws all from the top side with a single hex driver. Soft rubber feet are included which reduces vibration.
The motor mounts can be used in the craddle method with carbon fiber brace, battery tape, and standoffs. Simply tighten down two screws to hold the motor. (The carbon fiber brace, battery tape, and standoffs can be seen in the pictures above.)
The kits will be offered in 2 versions: with or without the rear axle assembly. We've designed the motor bulkhead adapter to be able to accommodate most motor bulkheads (1/10th or 1/12th). So if you have an old pan car, you can use it's bulkheads, and the rear axle assembly and choose the lower cost kit.
The items to the right side of the picture and in italics below come with the full kit with the rear axle assembly.
Both the Eagle Tree and Novak Sentry can export to Excel. Here are some example charts courteousy of John Stranahan. You can download the our Excel spreadsheet here.
A power supply adds the convenience of not having to wait to charge a battery and provides the same exact power on every test. Many power supplies have voltage adjustment. Personally, I race single cell, so I bought a Mean Well 5V 120A (HRP-600-5)_power supply. This particular power supply allowed me to adjust the voltage down to 4.220V. Bonus!
Of course, the final testing will always be the track, but when all things are equal, a dyno can offer some benefits.
The overall goal is simple: spin the slave motor as fast as you can with the least amount of amp draw. That will be your fastest and most efficient setup which will keep the motor cooler, leave more juice in the battery, and fall off less at the end of the race.
Let us know if you have any questions!