pstar, Welcome to EP!
Is remote control of the pictured device **possible**?
Absolutely!
Is it possible to plug in an aftermarket RF wireless device of some kind which would afford remote speed control?
Simply Put: NO.
Why?
In short, mass-market consumer electronics give people the impression that all electronics are cheap, this simply isn't the case. A typical consumer-mass-market electronic device has thousands of man-hours invested (by inventors, researchers, designers, engineers, manufacturing personnel, marketing professionals, sales people etc, etc). The resulting product is fully optimized for everything from mass production to shipping in such a way that it enters the market at a reasonable "perceived value". The cost in man-hours to prepare an electronic mass-market item for sale could easily exceed $1M, in the case of something like "smart phones" the cost could be an order of magnitude or TWO more than that.....but if there is a market for 50,000,000 pieces then even a $100M initial investment only adds $2/unit to the cost of the phone.... But if you only wanted 1 phone, it would likely still take the same $100M in R&D to produce it.
In your proposed "simple remote control speed product": it is NOT a mass market product, but rather a "specialty item". "Specialty Items" require all most all of the same steps and man-hours as a mass-market product, but if you only expect the market to be 10,000 units, and you have 10,000 man-hours tied up in development at an average of $75/hr the cost of the unit starts @ $75 before you begin adding the cost of production, shipping, and, let's not forget "profit"....not just for the manufacturer, but also everyone in the distribution chain (wholesaler/retailer/marketing)....so even if the product only "costs" $20 to "make", the real "cost" to the MFG is $75 + $20 = $95 ..... Assuming the MFG wants to make a 40% profit, they might sell the item to "wholesalers" for $95/0.6 => $158.33 + Freight let's call it $165. If the Wholesaler works on a 30% mark-up then they would sell it to retailers @ $165/0.7 ==> $235.71 + Freight .... let's call it $240 to the retailer, then let's say the retailer works on a 40% margin, so the retailer offers the product to the public for $240/0.6 ==> $400 (oh, it is a retailer, $399.99!).
Most consumers see something "simple" like the PWM PCB you purchased on e-bay (likely for ~$20) and they see various "RF Modules" on e-bay for ~$10 and think, "If I just knew which one to order I could get this speed control for $30 instead of paying the ridiculous $399 for the factory made version ...." But the trouble is in the details. To get the $30 PCB and the $10 RF modules to function like you want them to will require **best case** (ASS-U-MEing you have extensive knowledge in RF protocols and are adept at uController programming and have adequate skills in fabrication and implementation of electronic circuits to achieve a functional interface) hundreds of man-hours to achieve. However, if you have the a fore mentioned skills, your time is likely worth > $25/hr and even 20 hours invested would make the "Factory Price" of $399 seem reasonable.....
But don't despair, there is one other option that **MIGHT** make your project viable.... "Open Source" projects are a relatively new phenomena that are fundamentally changing the world. In an "Open Source" project an individual or group of individuals "shares" their work in the public domain thus making it MUCH easier for other's to copy or extend their work. IF there is an "Open Source Project" already in existence addressing this (or a similar application) it has the potential to dramatically reduce the time-overhead of such a project .... Still likely to exceed the a fore mentioned 20 hours, and would almost certainly require learning about uControllers, Electronics and Fabrication, but might be viable if you consider the learning process worthwhile.
Good Luck!
Fish
