Running Higher loads than a single 550, 775, 887, or 895 motor per channel on Speed Squirrel V3 and earlier

Introduction

The Speedy Squirrel speed controller was designed to handle one moderately loaded 775 motor per channel. After I had completed the design I became more involved in the power wheels modified community and found that driving a single 775 motor per wheel on a 2WD kids toy was just scratching the surface. I found there were first gear deleted power wheels 7R gear boxes that took one or two motors each and the RS775 gear box. All of those drew more power than initially designed (24V LiFePo4 input voltage and a single 775 motor per channel was the original target).

What is the Problem?

When drawing more current that a single moderately loaded 775 (Specifically Traxxas Titan Motors) (stock gearing in a power wheels 7R gearbox) at 28V (24V LiFePo4), the capacitors on the board need to work harder to keep up with the switching voltage. The output of the controller is connecting the input voltage (Battery Power) ON and OFF very fast for different amounts of time, that is how it generates variable speed by varying the output power.

Capacitors with a 24VDC input and 30A load at 50% Duty Cycle

How the Capacitor Bank works and how it helps

What Makes the Problem Worse?

This issue is amplified if you have low quality battery cells (Higher internal resistance), running a higher voltage that the motors can handle and limiting the speed, and the worse one of all, too small and too long of battery cables.

What Should to do?

If you are set on running a speed controller with first gear delete gear boxes and / or multiple motors (Running single motor in first gear delete box will stress the capacitors as well) you can add a capacitor bank to the input of the board (Not the motors outputs, battery input). You want at least six parallel capacitors and be rated for >40V, look for an RC capacitor bank rated for 12S batteries like the one linked below. That Capacitor bank should have 12AWG or 10AWG wires connected to it.

https://rcjuice.com/products/hobbystar-capacitor-pack-13200uf-for-2s-12s

Same load with additional Cap Bank

How to Install

• Wire the Cap Bank to the inside terminals on the main input power terminal block

  • The closer the cap bank wires stay together the better results

• Cut the cap bank leads as short as practical, the shorter the better

  • Longer leads increase inductance, you are filtering high frequency power

Example with cap bank installed